Synthesis and biological evaluation of fluorescent GAT-ligands based on meso-substituted BODIPY dyes

Article abstract of DOI:10.1007/s00044-019-02483-6

BODIPY dyes are well known for their outstanding spectroscopic properties and are therefore established in a range of fluorescence based analysis techniques for in vitro as well as for in vivo measurements. For the first time, we designed and synthesized a series of fluorescent ligands for the SLC6 family transporters mGAT1–mGAT4 based on BODIPY dyes as fluorogenic subunits. In the novel series of fluorescent compounds, BODIPY dye subunits are linked with an alkyl chain of three to five carbon atoms that originates from the meso-position of the BODIPY dye to the amino function of different cyclic amines. Screening of these fluorescent probes for their biological activity as GABA uptake inhibitors of mGAT1–mGAT4 revealed ligands with pIC₅₀ values up to 5.35.

Full text of DOI:10.1007/s00044-019-02483-6

MEDICINAL
CHEMISTRY
RESEARCH
Medicinal Chemistry Research
https://doi.org/10.1007/s00044-019-02483-6
ORIGINAL RESEARCH
Synthesis and biological evaluation of fluorescent GAT-ligands
based on meso-substituted BODIPY dyes
Markus Daerr1 Jörg Pabel Georg Höfner Peter Mayer Klaus T. Wanner
1 ●
1 ●
1 ●
1
●
Received: 28 August 2019 / Accepted: 23 November 2019
©
Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract
BODIPY dyes are well known for their outstanding spectroscopic properties and are therefore established in a range of
fluorescence based analysis techniques for in vitro as well as for in vivo measurements. For the first time, we designed and
synthesized a series of fluorescent ligands for the SLC6 family transporters mGAT1–mGAT4 based on BODIPY dyes as
fluorogenic subunits. In the novel series of fluorescent compounds, BODIPY dye subunits are linked with an alkyl chain of
three to five carbon atoms that originates from the meso-position of the BODIPY dye to the amino function of different
cyclic amines. Screening of these fluorescent probes for their biological activity as GABA uptake inhibitors of
mGAT1–mGAT4 revealed ligands with pIC50 values up to 5.35.
●
●
●
●
●
Keywords BODIPY Fluorescent ligand GABA transporters GAT γ-aminobutyric acid Biological activity
Introduction
exist in humans and other species (Borden et al. 1992;
Guastella et al. 1990). Since the biological test system
operated in our group is based on GATs originating from
mouse cells, the nomenclature established for the GABA
transporters of this species, with the subtypes being denoted
as mGAT1 (=SLC6A1), mGAT2 (=SLC6A12), mGAT3
(=SLC6A13), and mGAT4 (=SLC6A11) will be used in this
manuscript (Liu et al. 1993). Of the four GABA transporter
subtypes, which differ in their distribution in brain and body,
mGAT1 and mGAT4 are clearly predominating in the brain
where they mediate neuronal and glial reuptake of GABA
(Borden 1996; Zhou and Danbolt 2013). In contrast, the
expression levels of mGAT2 and mGAT3 are very low in
brain and confined to specific brain regions, i.e. both trans-
porter subtypes are restricted to the leptomeninges, addi-
tionally mGAT3 exists in a subset of blood vessels. Hence,
these transporters that are present in high densities in liver
and kidneys are not likely to significantly contribute to
GABA inactivation in the brain (Kempson et al. 2014; Zhou
and Danbolt 2013; Zhou et al. 2012).
γ-Aminobutyric acid (GABA) is the major inhibitory neu-
rotransmitter in the mammalian central nervous system. One
mechanism to regulate GABA neurotransmission is the
inhibition of GABA reuptake from the synaptic cleft into
nerve axons and glial cells mediated by GABA transporters
(
GATs) (Kristensen et al. 2011). Hence, GATs form
important drug targets for the treatment of diseases of the
central nervous system associated with decreased levels of
GABA like epilepsy (Treiman 2001), M. Parkinson (Ishi-
wari et al. 2004), M. Alzheimer (Rissman et al. 2007),
Chorea Huntington (Frank 2014), depression (Kalueff and
Nutt 2007), anxiety (Zwanzger and Rupprecht 2005), and
insomnia (Plante et al. 2012).
The GATs are membrane bound transporter proteins of
the SLC6 family, and four distinct subtypes are known to
Supplementary information The online version of this article (https://
doi.org/10.1007/s00044-019-02483-6) contains supplementary
material, which is available to authorized users.
Fluorescent labels and probes addressing a target of
interest such as a GPCR, a ligand gated ion channel, or a
transport protein are tool compounds of high value. With
such compounds, a plethora of biological studies may be
performed, which in particular is true when these com-
pounds retain the pharmacological profile of the parent
unlabeled ligands of the target of interest, they have been
delineated from (Leopoldo et al. 2009).
*
Klaus T. Wanner
klaus.wanner@cup.uni-muenchen.de
1
Department of Pharmacy - Center for Drug Research, Ludwig-
Maximilians-Universität München, Butenandtstr. 5-13,
Munich 81377, Germany

Medicinal Chemistry Research
In confocal laser scanning microscopy experiments,
fluorescent ligands are required in order to monitor pro-
cesses triggered by ligand-receptor interactions in living
cells such as internalization, trafficking, sequestration, and
recycling. Fluorescent ligands are also indispensable in
fluorescence correlation spectroscopy experiments provid-
ing subtle and specific differences in receptor binding
characteristics between different areas of membranes of the
same cell (Briddon and Hill 2007).
In fluorescence binding assays fluorescent probes may
serve as reporter ligands similar to the function of radi-
oligands in radioligand binding assays, whereby these
assays have the clear advantage that they are devoid of any
risks associated with the handling of radioactive com-
pounds. Fluorescence polarization assays make use of
fluorescent probes as well to monitor ligand-target bind-
ing. They are an attractive alternative to radioligand and
fluorescence binding assays, as no separation of the
ligand-target complex from the incubation system for the
quantification of bound reporter-ligand is required (Leo-
poldo et al. 2009).
Furthermore, fluorescent ligands are also indispensable
tool compounds in fluorescence resonance energy transfer
(FRET) experiments, a method frequently used for in depth
studies of protein dynamics and protein-protein interactions
(Sohail et al. 2016; Stockmann et al. 2017).
Hence, we envisaged it worthwhile to develop fluor-
escent ligands binding to GABA transporter proteins and to
investigate their binding characteristics with our MS
Binding and GABA uptake assays (Zepperitz et al. 2006;
Kragler et al. 2008). The developed fluorescence ligands
with known affinity to the GATs should be useful tool
compounds for biological studies of GATs employing the
different fluorescence-based techniques described above.
For the design of these fluorescent compounds, we con-
sidered structural features of five representative GAT inhi-
bitors 1–5 (Fig. 1a) which are Tiagabine (1), SKF 89976-A
(2), NNC 05-2090 (3), NNC 05-2045 (4), and SNAP-5114
3
Fig. 1 a Structures of known GAT inhibitors Tiagabine (1), SKF
represent remaining [ H]GABA uptake in the presence of 100 µM test
8
5
9976-a (2), NNC 05-2090 (3), NNC 05-2045 (4), as well as SNAP-
114 (5); pIC50 values were determined using the same standard
compound. b General Structure of the target compounds with a
BODIPY dye based fluorogenic subunit
a)
assay as for all tested compounds (Kragler et al. 2008). Percentages

Medicinal Chemistry Research
(
5). Tiagabine (1), which is marketed as a drug (Gabitril®),
moiety” of lead structures 1–5. The pyrrole rings of the
BODIPY dyes can be considered as a substitute for the
aromatic rings present in 1 or 2 five- and six-membered
aromatic ring systems, even though the core of the BODIPY
dyes is more rigid, whereas their similarity to the tricyclic
ring system in 3 and 4 is even higher. Like in the known
GAT inhibitors, the used BODIPY dyes should finally be
linked to the cyclic amine moiety by an alkyl spacer with
varying length, from three to five carbons, that originate
from the 8-position of the BODIPY, which is also called
“meso-position”.
In addition to the “aryl moiety” and linker, known GAT
inhibitors vary also with respect to the cyclic amino or
amino acid group representing the polar subunit of the
overall compound. Therefore, we intended to also vary the
structure of the cyclic amino and amino acid subunits.
Hence, in addition to piperidine as the most basic six
membered cyclic amine also substituted derivatives thereof
should be employed in the synthesis.
and SKF 89976-A (2) are selective inhibitors of mGAT1.
NNC 05-2090 (3) as well as NNC 05-2045 (4) are described
in literature as potent inhibitors of mGAT2 (Borden et al.
1
994; Thomsen et al. 1997). NNC 05-2090 (3) is even
described as subtype selective at mGAT2, yet a subtype
selectivity of 3 could not be confirmed in our test system
(
see Table 2). SNAP-5114 (5) on the other hand is one of
the most potent inhibitors known so far for mGAT4 (Dhar
et al. 1994). Although the design of the fluorescent GABA
inhibitors was based on compounds 1–5 as representative
examples for the various classes of GAT inhibitors with
certain subtype selectivities for the individual GAT sub-
types, the development of subtype selective fluorescent
ligands was not our primary focus. Rather by a first series of
fluorescent GAT inhibitors, the suitability of the concept
pursued for the design of fluorescent GAT inhibitors should
be verified. In addition, also fluorescent GAT inhibitors
lacking or having only low subtype selectivity may serve as
valuable tool compounds providing data specific for a single
GAT subtype as the specificity may also be warranted by
employing target systems containing only the GAT subtype
of interest as it is the case when the appropriate cell lines
expressing the respective target are used.
As such more polar derivatives, compounds with an ether
function (7b) or an additional OH group (7c, 7d) or more
lipophilic derivatives exhibiting an aryl substituent (7e, 7f),
should be employed. In addition, piperidine derivatives with
both, i.e. possessing an OH function and an aryl residue
(7g–7k), but also those exhibiting either a carboxylic acid
ester moiety (7l) should be used as building blocks, whereas
compounds with a carboxylic acid function (7m) should be
accessed via the corresponding carboxylic acid esters.
Overall, this should lead to BODIPY dye residues con-
taining compounds displaying polar subunits well known
from common GAT inhibitors (see e.g. 1–5, Fig. 1).
In summary, this study envisaged fluorescent GAT
ligands with the general structure 6 comprising a BODIPY
dye unit linked with a cyclic amine moiety through an alkyl
spacer originating from the meso-position of the BODIPY
dye. The synthesis of these compounds should be accom-
plished by reaction of the respective BODIPY precursors
exhibiting an alkyl chain with a terminal leaving group
originating from the meso-position with amines 7a–m to
finally study the potencies of the final products at
In general, GAT inhibitors are composed of a cyclic
amine or a cyclic amino acid like nipecotic acid (7m) and an
“
aryl moiety” connected by a linker of variable length ori-
ginating from the amino nitrogen (Knutsen et al. 1999).
Typical representatives for mGAT1 selective compounds
like Tiagabine (1) and SKF 89976-A (2) (Fig. 1a) have two
aromatic rings as “aryl moiety”, whereas for mGAT2 the
corresponding “aryl moiety” is in general more rigid, the
two aromatic rings being bridged (see 3 and 4 Fig. 1a) to
give a carbazole unit. For mGAT4, on the other hand, the
“
aryl moiety” is represented by a trityl unit in the most
potent inhibitors like SNAP-5114 (5).
In the new fluorescent ligands for the GABA transporters
envisaged by us, the before mentioned “aryl moieties”
highlighted by bold lines in Fig. 1a should be replaced by a
fluorescent dye of comparable size and shape (6, Fig. 1b). A
group of fluorescent residues that we thought to fulfill these
conditions are difluoroboraindacene (boron dipyrro-
methene, BODIPY) derived subunits (Fig. 1b, bold struc-
ture). BODIPYs comprising a tricyclic ring system with a
central boradiazine ring flanked by two pyrrole units have
been introduced as a class of compounds in 1968 by Treibs
and Kreuzer (Treibs and Kreuzer 1968). BODIPY dyes are
known for their excellent thermal and photochemical sta-
bility as well as their outstanding spectroscopic properties
like high photostability, large extinction coefficients, and
high quantum yields (Loudet and Burgess 2007; Ulrich
et al. 2008). Moreover, with regard to their molecular size,
BODIPY dyes seem to be able to partially mimic the “aryl
3
mGAT1–mGAT4 in [ H]GABA uptake assays.
Materials and methods
Experimental
Unless noted otherwise, all reactions were performed in
oven-dried glassware under moisture-free conditions and
inert gas atmosphere. All commercial reagents were used
without further purification. For the reactions, dried and
freshly distilled solvents were used. NEt was dried over
3
sodium and distilled under nitrogen atmosphere when

Medicinal Chemistry Research
needed. CH Cl and MeCN were distilled from CaH under
was dried over Na SO , filtered, and the solvent was
2
2
2
2
4
nitrogen atmosphere. For chromatographic purposes, only
distilled solvents were used. Flash-chromatography (FC)
was performed according to Still et al. (1978) using silica
gel. NMR spectra were measured with a Jeol Eclipse + 400
removed. The remaining residue was purified by flash
chromatography.
GP-3 (Method B): nucleophilic substitution of 15b One
equivalent of BODIPY 15b and three equivalents of the
corresponding amine were dissolved in MeCN and the
reactor vessel was put in a preheated oil bath at 50 °C and
stirred for 14 h. Afterwards water was added and the reac-
tion mixture was diluted in EtOAc. The organic phase was
washed with H O and brine, dried over Na SO , filtered,
(
400 MHz) and +500 (500 MHz) spectrometer. The cou-
pling constants were stated with an accuracy of 0.5 Hz.
MestreNova was used for further analysis of the spectra. IR
spectra were recorded with a FT-IR spectrometer Paragon
1
000 (Perkin-Elmer) and Spectrum v2.00 software (Perkin-
Elmer) was used for analysis. Mass spectra were measured
with a Mass Spectrometer 59827A with 59980 Particle
Beam LC/MS interface (Hewlett Packard) or an Applied
LC–MS/MS Mass spectrometer API 2000. High-resolution
mass spectrometry (HRMS) was accomplished with an LTQ
FT (ThermoFinnigan) or a JMS GCmate II (Jeol).
2
2
4
and the solvent was removed. The remaining residue was
purified by flash chromatography.
GP-3 (Method C): nucleophilic substitution of 17 One
equivalent of BODIPY 17, 1.4 equivalents of the corre-
sponding amine, as well as three equivalents K CO were
2
3
Chemistry
solved in MeCN and stirred at 80 °C for 14 h. After cooling
to room temperature, the reaction mixture was filtered, and
the solvent was removed. The remaining residue was pur-
ified by flash chromatography.
General procedures
GP-1: Synthesis of BODIPYS One equivalent of the appro-
priate acid chloride 12, 13, or 14 was added dropwise to a
solution of two equivalents of 2,4-dimethylpyrrole (11) in
CH Cl under argon and stirred for 2 h at 50 °C. Afterwards,
GP-3 (Method D): nucleophilic substitution of 16 One
equivalent of BODIPY 16, 1.4 equivalents of the corre-
sponding amine as well as 2.5 equivalents KI and three
equivalents K CO were solved in MeCN and stirred at
80 °C for 14 h. After cooling to room temperature, the
reaction mixture was filtered, and the solvent was
removed. The remaining residue was purified by flash
chromatography.
2
2
the solvent was removed and the remaining residue was
resolved in a mixture of toluene and CH Cl (95:5), 4.8
2
3
2
2
equivalents of NEt were added and the mixture was stirred
3
at room temperature for 30 min under argon. After adding
of 6.9 equivalents of BF •OEt and heating at 50 °C for
3
2
1
.5 h, the solvent was removed and the remaining residue
was purified by flash chromatography.
Synthesis of compounds
GP-2: Ester hydrolysis One equivalent of the ester was
4-(2-Methoxyphenyl)piperidin-4-ol (7h) Compound 17
(900 mg, 2.64 mmol) solved in MeOH (18.0 mL) was
hydrogenated with 10% Pd/C (168 mg) at room temperature
for 30 min. After removal of the catalyst by filtration, the
filtrate was concentrated under reduced pressure to give
pure 7h.
solved in a solution mixture of CH Cl :MeOH (1:2) and 2.5
2
2
equivalents of aqueous solution of LiOH was added drop-
wise. The reaction mixture was stirred at room temperature
until no educt was detectable by thin layer chromatography.
Afterwards the pH was adjusted to pH = 7 by adding
phosphate buffer (pH = 7, 0.1 M) and extracted three times
with CH Cl . The organic phase was dried over MgSO ,
In total 578 mg (100%); white solid; mp 240 °C (dec.); IR
(KBr) νmax 3400, 3193, 2998, 2946, 2836, 2792, 2761,
2721, 2659, 2622, 2568, 2520, 2499, 2474, 2412, 2034,
1590, 1486, 1471, 1454, 1436, 1386, 1356, 1348, 1307,
2
2
4
and the solvent was removed. The remaining residue was
resolved in bidest. H O, filtered, and freeze-tried.
2
−
1
1
284, 1241, 1207, 1191, 1151, 1150, 1089, 1074, 1025 cm ;
1
GP-3 (Method A): nucleophilic substitution of 15a One
equivalent of BODIPY 15a, 1.4 equivalents of the corre-
sponding amine as well as 2.8 equivalents of KI and three
equivalents of K CO were solved in acetone and stirred at
H NMR (500 MHz, DMSO-D6, TMS): δ = 1.54 (d,
J = 13.7 Hz, 2H), 2.68 (td, J = 5.0/13.6 Hz, 2H), 3.08–3.20
(m, 4H), 3.81 (s, 3H, H C), 5.34 (s, 1H), 6.95 (td, J = 1.1/
3
7.6 Hz, 1H), 6.99 (dd, J = 0.9/8.2 Hz, 1H), 7.25 (ddd, J = 1.8/
2
3
13
1
00 °C for 18 h in a microwave reactor. Afterwards, the
7.4/8.1 Hz, 1H), 7.56 (dd, J = 7.7/1.7 Hz, 1H) ppm;
C
solution was diluted with EtOAc and extracted with satu-
rated citric acid. The pH of the aqueous phase was adjusted
to 7 by adding of phosphate buffer (pH = 7, 0.1 M) at 0 °C
NMR (125 MHz, DMSO-D6): δ = 31.4 (2C, NHCH CH C),
2
2
39.5 (2C, NHCH CH C) 55.2 (H C), 68.6 (NHCH CH C),
2
2
3
2
2
115.8 (CC C H), 120.2 (CC C HC HC H), 126.3 (CC
ar-
ar ar
ar ar
ar
ar
and extracted with CHCl afterwards. The organic phase
C HC H), 128.4 (CC C C H), 135.1 (CC C ), 156.1
ar ar ar ar ar ar ar
3

Medicinal Chemistry Research
+
(
(
CC C ) ppm; M (C H NO ) = 207.13 MS (CI, CH ) m/z
ppm; M (C H BF N ) = 373.3 MS (EI 70 eV) m/z (%):
21 30 2 3
ar ar
12 17
2
5
+
+
+
%): 208.05 (18, [M+H] ), 190.05 (100); HRMS (EI+): M
373.4 (M , 22), 262.25 (51), 98.25 (100), 55.10 (55);
calc. for C H NO , 207.1254; found: 207.1258.
HRMS (FAB, NBA): [M+H]+ calc. for C H BF N ,
1
2
17
2
21 31
2
3
+
3
74.2574; found: 374.2570 (M+H) .
4-(2-Chlorphenyl)piperidin-4-ol (7j) 23 (312 mg, 1.00 mmol)
was solved in Et O (10.0 ml) at 0 °C and HCl in Et O
5,5-Difluor-1,3,7,9-tetramethyl-10-(3-morpholinopropyl)-
2
2
4
4
(
10.0 mmol, 5.0 mL, 2 M) was added dropwise. The resulting
5H-4 λ ,5 λ -dipyrrolo[1,2-c:2',1'-f][1,3,2]diazaborinin-4-ium-
5-uide (8b) According to GP-3 (Method A): Compound
15a (100 mg, 308 µmol) and morpoline (7b) (37.6 mg,
432 µmol, 38.0 µL) as well as KI (143.4 mg, 864 µmol) and
K CO (132 mg, 956 µmol) in acetone (5.0 mL). Flash-SC
reaction mixture was stirred for 1 h at 0 °C and was then
allowed to warm up to room temperature and stirred over-
night. The solvent was removed, and the resulting residue
was solved in H O (2.0 ml) and cooled to 0 °C. K CO
2
2
3
2
3
(
207 mg, 1.50 mmol) was added as well as DCM (10.0 ml)
(EtOAc/n-heptane 6:3, 10% NEt3).
and the mixture was stirred vigorously at room temperature
63 mg (54%); red solid; mp 143–144 °C; DC: R = 0.4
f
for 1 h. The aqueous phase was removed with Na SO , fil-
(EtOAc/n-heptane = 6:3, 10% NEt ); IR (KBr) ν
3434,
2
4
3
max
tered, and the solvent was removed.
03 mg (96%); white solid; mp 164–167 °C; IR (KBr)
νmax 3419, 3289, 3266, 3055, 2995, 2944, 2933, 2858,
2919, 2852, 2802, 2360, 2341, 1548, 1506, 1473, 1409,
−
1 1
2
1367, 1340, 1305, 1201, 1162, 1156, 1079, 1058 cm ; H
NMR (500 MHz, DMSO-D6, TMS): δ = 1.63–1.74 (m,
2H), 2.42 (m, 18H), 2.93–3.03 (m, 2H), 3.55 (t, J = 4.4 Hz,
2
1
1
804, 2629, 1469, 1463, 1443, 1426, 1369, 1355, 1321,
1
3
321, 1278, 1232, 1200, 1161, 1134, 1142, 1157, 1091,
4H), 6.23 (s, 2H) ppm; C NMR (125 MHz, DMSO-D6,
−
1
1
064, 1041, 1025, 1000 cm ; H NMR (500 MHz,
TMS): δ = 14.0 (2C, NCCH ), 15.8 (2C, CCCH ), 26.0
3
3
CD Cl , TMS): δ = 1.85–1.90 (m, 2H), 2.23–2.31 (m,
(CCH ), 28.5 (CCH CH ), 53.5 (2C, NCH CH O), 58.2
2
2
2 2 2 2 2
2
7
H), 2.89–2.95 (m, 2H), 3.10 (td, J = 2.7/12.3 Hz, 2H),
.19–7.24 (m, 1H), 7.29 (td, J = 1.5/7.6 Hz, 1H), 7.37 (dd,
(CCH CH CH N), 66.1 (2C, NCH CH O), 121.6 (2C,
2 2 2 2 2
CCHC), 130.7 (2C, CHCCC) 140.7 (2C CCHCCC),
1
3
19
J = 1.4/7.9 Hz, 1H), 7.61 (dd, J = 1.7/7.9 Hz, 1H) ppm;
NMR (125 MHz, CD Cl ): δ = 36.4 (2C, NHCH CH C),
C
146.7 (NCCCH ), 152.9 (2C, NCCH) ppm; F NMR
2
11
(470 MHz, CDCl ): δ = −143.1 to −143.4 (m) ppm;
B
2
2
2
2
3
4
2.4 (2C, NHCH CH C), 72.6 (CH C), 127.6 (CC C H-
NMR (160 MHz, CDCl ): δ = −1.82 (t, J = 33.2 Hz) ppm;
2
2
2
ar ar
3
C H), 127.7 (CC C H), 128.8 (CC C HC HC H), 132.1
M (C H BF N O) = 375.23 MS (EI, 70 eV) m/z (%):
ar
ar ar
ar ar
ar
ar
20 28
2
+
3
(
(
(
CC C C H), 132.3 (CC C ), 144.5 (CC C ) ppm; M
375.25 (22, M ), 262.25 (93), 247.25 (30), 242.25 (42),
ar ar ar
ar ar
ar ar
+
229.25 (11). HRMS (EI+): M+ calc. for C H BF N O,
C H ClNO) = 211.08 MS (CI, CH ) m/z (%): 212.15
1
1
14
5
20 28
2
3
+
+
38, [M+H] ), 196.15 (32), 194.15 (100); HRMS (EI+): M
375.2288; found: 375.2295.
calc. for C H ClNO, 211.0758; found: 211.0772.
1
1 14
5
,5-Difluoro-10-[3-(3-hydroxypiperidin-1-yl)propyl]-1,3,7,9-
4
4
5
,5-Difluoro-1,3,7,9-tetramethyl-10-[3-(piperidin-1-yl)pro-
tetramethyl-5H-4 λ ,5 λ -dipyrrolo[1,2-c:2′,1′-f][1,3,2]diaza-
borinin-4-ium-5-uide (8c) According to GP-3 (Method B):
Compound 15b (136 mg, 295 µmol) and 3-hydroxypiperidine
(7c) (90.0 mg, 885 µmol) in MeCN (2.5 mL). Flash-SC
(EtOAc, 1% MeOH, 5% NEt3).
4
4
pyl]-5H-4 λ ,5 λ -dipyrrolo[1,2-c:2′,1′-f][1,3,2]diazaborinin-
4-ium-5-uide (8a) According to Method B: Compound
15b (136 mg, 295 µmol) and piperidine (7a) (73.0 mg,
885 µmol, 84.0 µL) in MeCN (2.5 mL). Flash-SC (n-hep-
tane/EtOAc = 8:1, 10% NEt3).
7 mg (80%); orange solid; mp 168–169 °C; DC: R =
93 mg (81%); orange solid; mp 171 °C; DC: R = 0.2
f
8
(EtOAc, 1% MeOH, 5% NEt ); IR (KBr) ν
3565, 3547,
f
3
max
(
0.3); IR (KBr) νmax 3432, 2933, 2848, 2802, 2757, 2360,
3473, 3119, 2935, 2857, 2803, 2760, 1548, 1507, 1474,
1
1
546, 1506, 1475, 1442, 1409, 1369, 1338, 1303, 1278,
201, 1160, 1116, 1101, 1060 cm ; H NMR (400 MHz,
1409, 1368, 1337, 1305, 1277, 1224, 1202, 1161, 1096,
−
1
1
−1 1
1080, 1061, 1028 cm : H NMR (500 MHz, DMSO-D6,
TMS) δ = 0.99–1.09 (m, 1H), 1.38 (dd, J = 24.6/12.3 Hz,
1H), 1.55–1.89 (m, 6H), 2.40 (s, 8H), 2.43 (s, 6H), 2.69 (d,
J = 11.0 Hz, 1H), 2.86 (d, J = 7.8 Hz, 1H), 2.97 (dd, J =
5.7/11.6 Hz, 2H), 3.39–3.48 (m, 1H), 4.60 (d, J = 4.1 Hz,
CD Cl , TMS): δ = 1.42 (m, 2H), 1.50–1.58 (m, 4H),
1
6
2
2
.70–1.81 (m, 2H), 2.40 (m, 6H), 2.45 (s, 6H), 2.46 (s,
H), 2.95–3.03 (m, 2H), 6.09 (s, 2H) ppm;. 13C NMR
(
(
100 MHz, CD Cl , TMS): δ = 14.6 (2C, H CCN), 16.6
2 2 3
2C, H CCCN), 24.9 (NCH CH CH ), 26.5 (2C,
1
3
1H), 6.23 (s, 2H) ppm; C NMR (125 MHz, DMSO-D6,
3
2
2
2
NCH CH CH ), 27.1 (CCH ), 29.8 (CCH CH ), 55.4
TMS) δ = 14.0 (2C, NCCH ), 15.8 (2C, NCCCH ), 23.2
2
2
2
2
2
2
3
3
(
2C, CH NCH CH CH ), 59.6 (CCH CH CH N), 121.9
(NCH CH CH CH), 26.1 (CCH ), 28.9 (CCH CH ), 33.3
2
2
2
2
2
2
2
2 2 2 2 2 2
(
1
2C, CCHC), 131.8 (2C, CHCCC), 141.3 (2C, H CCCN),
(NCH CH CH CH), 53.2 (NCH CH CH CH), 57.9
2 2 2 2 2 2
(CCH CH CH ), 61.7 (NCH CH), 66.0 (NCH CH), 121.5
2 2 2 2 2
3
9
1
47.5 (CCC), 154.0 (2C, H CCN) ppm; F NMR
3
(
470 MHz, CD Cl ): δ = −146.2 to −146.8 (m) ppm;
(2C, CCHC), 130.7 (2C, NCCCH ), 140.7 (2C, NCCCH),
2
2
2
1
1
19
B NMR (160 MHz, CD Cl ): δ = −2.24 (t, J = 33.0 Hz)
146.9 (NCCCH ), 152.9 (2C, NCCH ) ppm; F NMR
2
2
2
3

Medicinal Chemistry Research
(
470 MHz, DMSO-D6) δ = −143.1 to −144.7 (m) ppm;
NCH CH CH), 59.2 (CCH CH CH N), 121.9 (2C, CCHC),
126.4 (C C HC HC H), 127.2 (2C, C C HC HC H),
ar ar ar ar ar ar ar ar
128.7 (2C, C C HC HC H), 131.9 (2C, NCCCH ),
ar ar ar ar 3
2
2
2
2
2
1
1
B NMR (160 MHz, DMSO-D6) δ = −2.42 (t, J =
3.1 Hz) ppm; M (C H BF N O) = 389.25. MS (CI,
3
21
30
2
3
+
+
CH ) m/z (%): 390.25 (19, [M+H] ), 370.25 (100);
HRMS (EI+): M calc. for C H BF N O, 389.2445;
found: 389.2449; C H BF N O (389.25): calc. C 64.79, H
141.2 (2C, NCCCH ), 147.1 (C C HC HC H), 147.4
2 ar ar
5
ar ar
19
+
(NCCCH ), 154.1 (2C, NCCH ) ppm; F NMR (470 MHz,
2 3
21
30
2
3
1
1
CD Cl ): δ = −146.0 to −146.9 (m) ppm; B NMR
21
30
2
3
2 2
7
.77 N 10.79; found. C 64.63, H 7.69, N 10.63.
(160 MHz, CD Cl ): δ = −2.29 (t, J = 33.0 Hz) ppm; M
2 2
+
(
C H BF N ) = 449.28; MS (CI, CH ) m/z (%): 450.20
27 34 2 3 5
4
4
+
+
1
-[3-(5,5-Difluoro-1,3,7,9-tetramethyl-5H-4λ ,5λ -dipyrrolo
(19, [M+H] ), 430.25 (100); HRMS (EI+): M calc. for
[
(
1,2-c:2′,1′-f][1,3,2]diazaborin-in-10-yl)propyl]piperidin-4-ol
8d) According to GP-3 (Method B): Compound 15b
C H BF N , 449.2808; found: 449.2815. C H BF N
(449.28) calc. C 72.16, H 7.63, N 9.35; found: C 71.88, H
7.63, N 9.33.
2
7
34
2
3
27 34
2
3
(
8
136 mg, 295 μmol) and 4-hydroxypiperidine (7d) (90.0 mg,
85 μmol) in MeCN (2.5 mL). Flash-SC (EtOAc, 1%
MeOH, 5% NEt3).
4.0 mg (82%); orange solid; mp 159–161 °C; DC:
R = 0.28 (EtOAc, 1% MeOH, 5% NEt ); IR (KBr) ν
5,5-Difluor-1,3,7,9-tetramethyl-10-{3-[4-phenyl-5,6-dihydro-
4
4
9
pyridin-1(2H)-yl]propyl}-5H-4 λ ,5 λ -dipyrrolo[1,2-c:2′,1′-f]
[1,3,2]diazaborinin-4-ium-5-uid (8f) According to GP-3
(Method B): Compound 15b (136 mg, 295 µmol) and 4-
Phenyl-1,2,3,6-tetrahydropyridine (7f) (141 mg, 885 µmol)
in MeCN (2.5 mL). Flash-SC (1. n-Heptan/EtOAc 7:2, 10%
f
3
max
3
579, 3444, 2940, 2805, 2805, 2358, 1635, 1546, 1506,
−
1
1
475, 1409, 1369, 1340, 1305, 1203, 1162, 1078 cm ;
1
H NMR (500 MHz, DMSO-D6, TMS): δ = 1.36 (td, J =
3
.4/12.6 Hz, 2H), 1.61–1.73 (m, 4H), 2.03 (t, J = 10.9 Hz,
H), 2.40 (s, 8H), 2.42 (s, 6H), 2.72 (d, J = 10.3 Hz, 2H),
.92–3.05 (m, 2H), 3.42 (s, 1H), 4.55 (d, J = 3.8 Hz, 1H),
NEt ; 2. Gradient n-heptane/EtOAc 7:2 → n-heptane/
EtOAc 7:2, 10% NEt3).
3
2
2
6
99 mg (75%); orange solid; mp 157–160 °C; DC: R =
f
1
3
.23 (s, 2H) ppm; C NMR (125 MHz, DMSO-D6,
0.3 (n-heptane/EtOAc 7:2, 10% NEt ); IR (KBr) ν
3
max
TMS): δ = 14.0 (2C, H CCCN), 15.7 (2C, H CCN),
3425, 3080, 3056, 2950, 2923, 2867, 2824, 2768, 2732,
1654, 1638, 1596, 1549, 1534, 1509, 1473, 1444, 1407,
1365, 1345, 1307, 1276, 1203, 1160, 1136, 1113, 1100,
3
3
2
6.1 (CCH CH CH N), 29.2 (CCH CH CH N), 34.4
2 2 2 2 2 2
(
(
2C, NCH CH CH), 51.3 (2C, NCH CH CH), 57.7
2 2 2 2
−
1
1
CCH CH CH N), 66.2 (NCH CH CH), 121.5 (2C,
1079, 1058, 1027 cm ; H NMR (500 MHz, CD Cl ,
2 2
2
2
2
2
2
CCHC), 130.7 (2C, CHCC), 140.7 (2C, H CCCN),
TMS): δ = 1.82–1.90 (m, 2H,), 2.47 (s, 12H), 2.51–2.56
(m, 2H), 2.61 (t, J = 7.1 Hz, 2H), 2.71 (t, J = 5.7 Hz, 2H),
3.01–3.07 (m, 2H), 3.16 (dd, J = 2.8/6.1 Hz, 2H),
6.07–6.11 (m, 3H), 7.21–7.25 (m, 1H), 7.29–7.34 (m,
3
1
9
1
46.9 (CCC), 152.9 (H CCN) ppm;
F
NMR
3
(
470 MHz, DMSO-D6): δ = −143.6 to −143.9 (m) ppm;
B NMR (160 MHz, DMSO-D6): δ = −2.3 (t, J = 33.0)
1
1
1
3
ppm; M (C H BF N O) = 389.25. HRMS (ESI+): [M
2H), 7.40 (dt, J = 1.8/3.0 Hz, 2H) ppm; C NMR
(125 MHz, CD Cl , TMS): δ = 14.6 (2C, NCCH ), 16.6
2
1
30
2
3
+
+
3
H]
calc. for C H BF N O, 390.2523; found:
90.2523 (100, [M+H] ).
21 31 2 3
2
2
3
+
(2C, NCCCH ), 27.0 (NCCCH ), 28.5 (CHCCH ) 30.0
3 2 2
(
CCCH CH ), 50.9 (NCH CH CCH), 58.55 (NCH CHC),
2 2 2 2 2
5
,5-Difluoro-1,3,7,9-tetramethyl-10-[3-(4-phenylpiperidin-1-
121.95 (NCH CHC), 122.26 (2C, CCHC) 125.17 (2C,
2
4
4
yl)propyl]-5H-4 λ ,5 λ -di-pyrrolo[1,2-c:2',1'-f][1,3,2]diaza-
borinine (8e) According to GP-3 (Method B): Com-
pound 15b (136 mg, 295 μmol) and 4-Phenylpiperidine (7e)
CC C H), 127.4 (C C HC HC H), 128.7 (2C, C C H-
ar ar
ar ar
ar
ar
ar ar
C HC H), 131.8 (2C, NCCCH ), 135.3 (CC ), 141.2
ar
ar
2
ar
(2C, NCCCH ), 147.2 (NCCCH ), 154.1 (2C, NCCH )
3
2
3
1
9
(
143 mg, 885 μmol) in MeCN (2.5 mL). Flash-SC (1. n-
ppm; F NMR (470 MHz, CD Cl ): δ = −146.4 to
−146.6 (m) ppm; B NMR (160 MHz, CD Cl ): δ =
2 2
2 2
1
1
heptane/EtOAc 7:2, 10% NEt . 2. Gradient: n-heptane/
3
EtOAc 7:2 → n-heptane/EtOAc 7:2, 10% NEt3).
−2.32 (t, J = 33.0 Hz) ppm; M (C H BF N ) = 448.27;
27 34 2 3
+
+
1
16 mg (88%); orange solid; mp 167–168 °C; DC: R =
MS (CI, CH ) m/z (%): 448.20 (56, M ), 428.25 (100);
f
5
+
0
1
.27; IR (KBr) νmax 3424, 2933, 2901, 2821, 2766, 1548,
533, 1508, 1473, 1409, 1369, 1341, 1331, 1307, 1270,
HRMS (EI+): M calc. for C H BF N , 447.2652;
27
32
2
3
found: 447.2656.
−1
1
255, 1228, 1202, 1156, 1129, 1106, 1079, 1026, 1012 cm ;
1
H NMR (500 MHz, CD Cl , TMS): δ = 1.67–1.76 (m,
5,5-Difluoro-10-[3-(4-hydroxy-4-phenylpiperidin-1-yl)pro-
2
2
4
4
2
2
7
H), 1.77–1.84 (m, 4H), 2.09 (td, J = 2.4/11.7 Hz, 2H),
.43–2.54 (m, 15H), 2.99–3.05 (m, 4H), 6.09 (s, 2H),
.14–7.20 (m, 1H), 7.20–7.25 (m, 2H), 7.25–7.32 (m, 2H)
pyl]-1,3,7,9-tetramethyl-5H-4 λ ,5 λ -dipyrrolo[1,2-c:2′,1′-f]
[1,3,2]diazaborinin-4-ium-5-uide (8g) According to GP-3
(Method B): Compound 15b (136 mg, 295 µmol) and 4-
hydroxy-4-Phenylpiperidine (7g) (153 mg, 885 µmol) in
MeCN (2.5 mL). Flash-SC (n-heptane/EtOAc 5:4, 10%
NEt3).
1
3
ppm; C NMR (125 MHz, CD Cl , TMS): δ = 14.6 (2C,
2
2
NCCH ), 16.6 (2C, NCCCH ), 27.1 (CCH ), 30.0
3
3
2
(
CCH CH ), 34.0 (2C, CHCH ), 43.0 (CHC ), 55.1 (2C,
2 2 2 ar

Medicinal Chemistry Research
1
19 mg (87%); orange solid; mp 189–192 °C; DC: R =
(160 MHz, DMSO-D6): δ = −2.28 (t, J = 32.6 Hz) ppm; M
f
+
0
3
1
1
1
.27 (n-heptane/EtOAc 5:4, 10% NEt ); IR (KBr) νmax
533, 3423, 2943, 2818, 1546, 1530, 1506, 1474, 1448,
(C H BF N O ) = MS (CI, CH ) m/z (%): 496.40 (1, [M
3
28 36
2
3
2
5
+
+
+H] ), 83.00 (100), 85.00 (60); HRMS (EI+): M calc. for
406, 1370, 1304, 1275, 1229, 1203, 1156, 1138, 1108,
C H BF N O , 495.2863; found: 495.2869.
2
8
36
2
3
2
−
1 1
080 1044 cm ; H NMR (500 MHz, CD Cl , TMS): δ =
2
2
4
4
.71 (dq, J = 2.66/13.74 Hz, 2H), 1.82 (m, 2H), 2.09 (td,
1-[3-(5,5-Difluoro-1,3,7,9-tetramethyl-5H-4λ ,5λ -dipyrrolo
[1,2-c:2′,1′-f][1,3,2]diaza-borinin-10-yl)propyl]-4-(4-methox-
yphenyl)piperidin-4-ol (8i) According to GP-3 (Method A):
Compound 15a (100 mg, 308 µmol) and 4-(4-methox-
yphenyl)piperidin-4-ol (7i) (89 mg, 432 µmol, 38.0 µL), as
well as KI (143.4 mg, 864 µmol) and K CO (132 mg,
J = 4.5/13.2 Hz, 2H), 2.44–2.50 (m, 14H), 2.55 (t, J =
7
6
.0 Hz, 2H), 2.78 (d, J = 11.2 Hz, 2H), 3.00–3.07 (m, 2H),
.09 (s, 2H), 7.23–7.27 (m, 1H), 7.32–7.37 (m, 2H), 7.50
1
3
(
dt, J = 1.8/3.1 Hz, 2H) ppm; C NMR (125 MHz,
CD Cl , TMS): δ = 14.6 (2C, NCCCH ), 16.7 (2C,
2
2
3
2
3
NCCH ), 27.1 (CCH CH CH ), 30.0 (CCH CH CH ),
956 µmol) in acetone (5.0 mL). Flash-SC (EtOAc/n-heptane
3
2
2
2
2
2
2
3
9.0 (2C, NCH CH C), 50.3 (2C, NCH CH C), 59.1
5:4, 10% NEt3).
2
2
2
2
(
(
(
CCH CH CH N), 71.5 (CC ), 121.9 (2C, CCHC), 125.0
107 mg (70%); orange solid; mp 174–175; DC: R = 0.36
2
2
2
ar
f
2C, C C HC HC H), 127.3 (C C HC HC H), 128.6
(EtOAc/n-heptane 5:4, 10% NEt ); IR (KBr) ν
3434,
ar ar
ar
ar
ar ar
ar
ar
3
max
2C, C C HC HC H), 131.9 (2C, NCCCH), 141.2 (2C,
2921, 2813, 1610, 1550, 1509, 1471, 1407, 1371, 1305,
ar ar
ar
ar
−
1 1
NCCCH), 147.4 (NCCCH ), 149.1 (C ), 154.1 (2C,
1249, 1224, 1201, 1159, 1106, 1079, 1031 cm ; H NMR
(500 MHz, DMSO-D6, TMS): δ = 1.57 (d, J = 12.2 Hz,
2H), 1.72 (s, 2H), 1.86 (td, J = 4.1/12.8 Hz, 2H), 2.44 (m,
16H), 2.66 (d, J = 10.5 Hz, 2H), 2.96–3.08 (m, 2H), 3.73 (s,
3H), 4.68 (s, 1H), 6.24 (s, 2H), 6.87 (d, J = 8.8 Hz, 2H),
2
ar
1
9
NCCH) ppm; F NMR (470 MHz, CD Cl ): δ = −146.0
2
2
to −146.9) (m) ppm; 11B NMR (160 MHz, CD Cl ): δ =
2
2
−
2.28 (t, J = 33.0 Hz) ppm; M (C H BF N O) = 465.28
27 34 2 3
+
+
MS (CI, CH ) m/z (%): 466.20 (41, [M+H] ), 448.20
(
5
+
13
51), 446.30 (100) 428.25 (54); HRMS (EI+): M calc.
7.37 (d, J = 8.8 Hz, 2H) ppm; C NMR (125 MHz,
for C H BF N O, 465.2758; found: 465.2762;
DMSO-D6, TMS): δ = 14.0 (2C, NCCCH ), 15.8 (2C,
2
7
34
2
3
3
C H BF N O (449.28) calc. C 69.68, H 7.36, N 9.03;
NCCH ), 26.2 (CCH CH CH N), 29.1 (CCH CH CH N),
2
7
34
2
3
3
2
2
2
2
2
2
found: C 69.55, H 7.45, N 8.97.
38.1 (2C, NCH CH C), 49.6 (2C, NCH CH C), 54.9
2 2 2 2
(
H CO), 58.0 (CCH CH CH N), 69.1 (COH), 113.0 (2C,
3 2 2 2
4
4
1
-[3-(5,5-Difluoro-1,3,7,9-tetramethyl-5H-4λ ,5λ -dipyrrolo
C C HC HC HC O), 121.5 (2C, CCHC), 125.8 (2C,
ar ar ar ar ar
[
1,2-c:2′,1′-f][1,3,2] diazaborinin-10-yl)propyl]-4-(2-methox-
C C HC HC HC O), 130.7 (2C, NCCCH), 140.7
ar ar ar ar ar
(CH CC ), 142.1 (2C, NCCCH), 147.0 (NCCCH ), 152.9
2 ar 2
yphenyl)piperidin-4-ol (8h) According to GP-3 (Method
A): Compound 15a (100 mg, 308 µmol) and 4-(2-methox-
yphenyl)piperidin-4-ol (7h) (89.0 mg, 432 μmol, 38.0 μL),
as well as KI (143.4 mg, 864 μmol) and K CO (132.1 mg,
9
6
1
9
(2C, NCCH), 157.6 (C O) ppm; F NMR (470 MHz,
ar
1
1
DMSO-D6): δ = −144.0 to −143.6 (m) ppm; B NMR
(160 MHz, DMSO-D6): δ = −2.33 (t, J = 32.6 Hz) ppm; M
(C H BF N O ) = 495.28 MS (CI, CH ) m/z (%):
496.15 (1, [M+H] ), 140.20 (100); HRMS (EI+): M
calc. for C H BF N O , 495.2863; found: 495.2878;
2
3
+
56 μmol) in acetone (5.0 mL). Flash-SC (EtOAc/n-heptane
:3, 10% NEt3).
2
8
36
2
3
2
5
+
+
6
7 mg (44%); orange solid; mp 90 °C; DC: R = 0.2
f
28 36
2
3
2
(
EtOAc/n-heptane 6:3, 10% NEt ); IR (KBr) νmax 3441,
C H BF N O (495.28) calc. C 67.88, H 7.32, N 8.48;
28 36 2 3 2
3
2
1
924, 2816, 2768, 1549, 1510, 1472, 1409, 1372, 1307,
230, 1202, 1160, 1107, 1080, 1041, 1026 cm ; H NMR
found: C 67.65, H 7.44, N 8.41.
−
1 1
(
500 MHz, DMSO-D6, TMS): δ = 1.38 (d, J = 11.4 Hz,
4-(2-Chlorophenyl)-1-[3-(5,5-difluoro-1,3,7,9-tetramethyl-
4
4
2
2
4
8
1
1
H), 1.65–1.75 (m, 2H), 2.41 (s, 8H), 2.44–2.49 (m, 10H),
.66 (d, J = 9.8 Hz, 2H,), 3.02–3.10 (m, 2H), 3.80 (s, 3H),
.62 (s, 1H), 6.24 (s, 2H), 6.89–6.95 (m, 1H), 6.97 (d, J =
.2 Hz, 1H), 7.18–7.23 (m, 1H), 7.58 (dd, J = 1.7/7.7 Hz,
5H-4λ ,5λ -dipyrrolo[1,2-c:2',1'-f][1,3,2]diazaborinin-10-yl)
propyl]piperidin-4-ol (8j) According to GP-3 (Method B):
Compound 15b (136 mg, 295 µmol) and 4-(2-chlor-
ophenyl)-4-hydroxypiperidine (7j) (187 mg, 885 µmol) in
MeCN (2.5 mL). Flash-SC (n-heptane/EtOAc 4:5, 10%
NEt3).
1
3
H) ppm; C NMR (100 MHz, DMSO-D6, TMS): δ =
4.0 (2C, NCCH3), 15.8 (2C, NCCCH3), 26.3
(
CCH CH CH N), 29.2 (CCH CH CH N), 34.6 (2C,
110 mg (75%); orange solid; mp 212 °C; DC: R = 0.2 (n-
2
2
2
2
2
2
f
NCH CH C), 49.6 (2C, NCH CH C), 55.1 (H CO), 58.1
heptane/EtOAc 4:5, 10% NEt ); IR (KBr) ν 3561, 3447,
2
2
2
2
3
3
max
(
CCH CH CH N), 70.0 (COH), 115.6 (CC C H), 120.0
2966, 2939, 2925, 2819, 2865, 2771, 1544, 1507, 1469,
2
2
2
ar ar
(
1
CC C C H), 121.5 (2C, CCHC), 126.4 (C C C HC H),
ar ar ar ar ar ar ar
1434, 1408, 1374, 1304, 1274, 128, 1200, 1158, 1105,
−
1 1
27.7 (C C C HC HC H), 130.7 (2C, NCCCH), 136.7
1080, 1058, 1038 cm ; H NMR (500 MHz, TCl , TMS):
ar ar ar
ar
ar
4
(
(
CC C ), 140.8 (2C, NCCCH), 147.1 (NCCCH ), 152.8
δ = 1.82 (p, J = 6.4/6.8 Hz, 2H), 2.02 (d, J = 12.4 Hz, 2H),
2.31 (td, J = 4.0/13.0 Hz, 2H), 2.49 (s, 6H), 2.54 (s, 6H),
2.52–2.57 (m, 4H), 2.74–2.83 (m, 3H), 2.95–3.04 (m, 2H),
ar ar
2
19
2C, NCCH), 156.2 (CC C O) ppm; F NMR (470 MHz,
ar ar
11
DMSO-D6): δ = −144.0 to −143.6 (m) ppm; B NMR

Medicinal Chemistry Research
6
7
7
.08 (s, 2H), 7.23 (td, J = 7.6/1.6 Hz, 1H), 7.29 (td, J = 1.4/
850.0 µL) in MeCN (15.0 mL). Flash-SC (1. n-heptane/
.6 Hz, 1H), 7.38 (dd, J = 1.4/7.9 Hz, 1H), 7.54 (dd, J = 1.5/
EtOAc 8:1, 10% NEt , 2. Gradient: n-heptane/EtOAc 8:1 →
3
13
.9 Hz, 1H) ppm; C NMR (100 MHz, TCl , TMS): δ = 14.5
n-heptane/EtOAc 8:1, 10% NEt3).
4
(
2C, NCCH ), 16.4 (2C, NCCCH ), 26.0 (CCH CH CH N),
626 mg (79%); orange solid; mp 120 °C; DC: R = 0.2
3
3
2
2
2
f
2
8.3 (CCH CH CH N), 34.5 (2C, NCH CH C), 48.9 (2C,
(n-heptane/EtOAc 8:1, 10% NEt ); IR (KBr) ν
3385,
2
2
2
2
2
3
max
NCH CH C), 57.6 (CCH CH CH N), 71.1 (COH), 121.8
2936, 2807, 1360, 2342, 1729, 1549, 1510, 1474, 1409,
2
2
2
2
2
(
1
2C, CCHC), 127.0 (2C, CC C HC H), 127.3 (CC C ),
ar ar ar ar ar
1370, 1339, 1307, 1224, 1200, 1158, 1079, 1028, 985
cm ; H NMR (500 MHz, CD Cl , TMS): δ = 1.22 (t,
2 2
−
1
1
28.9 (CC C HC HC H), 131.2 (2C, NCCCH ), 131.6
ar ar
ar
ar
2
(
(
CC C C H), 140.5 (2C, NCCCH), 142.2 (CC ), 145.5
J = 7.1 Hz, 3H), 1.43 (dd, J = 3.0/11.5 Hz, 1H),
1.49–1.61 (m, 1H), 1.67–1.76 (m, 1H), 1.74–1.83 (m,
1H), 1.90 (d, J = 12.5, 1H), 2.05 (t, J = 10.5 Hz, 2H),
2.20 (t, J = 10, 1H), 2.44 (s, 6H), 2.46 (s, 6H), 2.48–2.56
(m, 3H), 2.72–2.80 (m, 1H), 2.97–3.03 (m, 3H), 4.09 (q,
ar ar ar
ar
19
NCCCH ), 154.1 (2C, NCCH) ppm; F NMR (470 MHz,
2
11
TCl ): δ = −144.7 to −146.3 (m) ppm;
B NMR
4
(
(
(
160 MHz): δ = −0.4 (t, J = 33.3 Hz) ppm;
C H BClF N O) = 499.23 MS (ESI+) m/z (%): 500.24
100, [M+H] ); HRMS (EI+): [M+H] calc. for
M
2
7
33
2
3
+
+
13
J = 7.1 Hz, 2H), 6.09 (s, 2H) ppm; C NMR (125 MHz,
+
C H BClF N O, 500.2446; found: 500.2451 [M+H] .
CD Cl , TMS): δ = 14.4 (CH CH ), 14.6 (2C, NCCCH ),
2
7
34
2
3
2
2
2
3
3
1
6.7 (2C, NCCH ), 24.9 (NCH CH CH CHCH ), 27.0
3 2 2 2 2
1
5
2
0-{3-[4-(4-Chlorophenyl)-4-hydroxypiperidin-1-yl]propyl}-
,5-difluoro-1,3,7,9-tetramethyl-5H-4 λ ,5 λ -dipyrrolo[1,2-c:
',1'-f][1,3,2]diazaborinin-4-ium-5-uide (8k) According to
(CCH CH CH N), 27.3 (NCH CH CH CHCH ), 29.7
2 2 2 2 2 2 2
(CCH CH CH N), 42.3 (NCH CH CH CHCH ), 54.4
2 2 2 2 2 2 2
4
4
(NCH CH CH CHCH ), 56.4 (NCHCH CH CHCH ),
2
2
2
2
2
2
2
GP-3 (Method B): Compound 15b (136 mg, 295 µmol) and
59.0 (CCH CH CH N), 60.6 (OCH CH ), 121.9, (2C,
2 2 2 2 3
4
8
4
-(4-Chlorophenyl)-4-hydroxypiperidine (7k) (187 mg,
85 µmol) in MeCN (2.5 mL). Flash-SC (n-heptane/EtOAc
:5, 10% NEt3).
CCHC), 131.8 (NCCCH ), 141.2 (2C, NCCCH), 147.2
2
1
9
(2C, NCCCH ), 154.1 (2C, NCCH), 174.2 (CO) ppm;
F
2
NMR (500 MHz, CD Cl ): δ = −146.3 to −146.7 (m)
2
2
1
1
1
29 mg (88%); orange solid; mp 189–192 °C; DC: R =
ppm; B NMR (160 MHz, CD Cl ): δ = −2.06 (t, J =
f
2 2
0
3
1
1
.29 (n-heptane/EtOAc 4:5, 10% NEt ); IR (KBr) ν
545, 3425, 2942, 2915, 2816, 1548, 1508, 1475, 1406,
33.0 Hz) ppm; M (C H BF N O ) = 445.27; MS (CI,
3
max
24 34
2
3
2
+
+
CH5 ) m/z (%): 446 (18, [M+H] ), 426 (100); HRMS
(ESI+): [M+H]+calc. for C H BF N O , 446.2785;
372, 1341, 1333, 1304, 1278, 1228, 1203, 1156, 1137,
2
4
35
2
3
2
−
1
1
108, 1092, 1043, 1011 cm ; H NMR (500 MHz,
found: 446.2781.
CD Cl , TMS): δ = 1.69 (d, J = 12.0 Hz, 2H), 1.77–1.85
2
2
(
1
3
m, 2H), 2.05 (td, J = 4.5/13.4 Hz, 2H), 2.41–2.50 (m,
10-[3-(3-Carboxypiperidin-1-yl)propyl]-5,5-difluoro-1,3,7,9-
4
4
4H), 2.55 (t, J = 7.0 Hz, 2H), 2.78 (d, J = 11.6 Hz, 2H),
.01–3.07 (m, 2H), 6.10 (s, 2H), 7.30–7.34 (m, 2H), 7.45
tetramethyl-5H-4 λ ,5 λ -dipyrrolo[1,2-c:2',1'-f][1,3,2]diaza-
borinin-4-ium-5-uide (8m) According to GP-2: Compound
8l (624 mg, 1.40 mmol) in 20.0 mL solvent mixture
(CH CL /MeOH, 2:1) and LiOH (83.80 mg, 3.54 mmol)
13
(d, J = 8.8 Hz, 2H) ppm; C NMR (125 MHz, CD Cl ,
2 2
TMS): δ = 14.6 (2C, NCCCH ), 16.7 (2C, NCCH ),
3
3
2
2
2
7.1 (CCH CH CH N), 29.9 (CCH CH CH N), 39.0 (2C,
solved in H O (3.5 mL). The reaction mixture was stirred
2
2
2
2
2
2
2
NCH CH C), 50.2 (2C, NCH CH C), 59.0 (CCH CH CH N),
for 6 d. The reaction mixture was diluted with CH Cl and
2
2
2
2
2
2
2
2
2
7
1.3 (COH), 121.9 (2C, CCHC), 126.7 (2C, C C HC H-
extracted three times with NaOH (0.1 M). Further work up
according to general procedure.
ar ar
ar
C HC Cl), 128.6 (2C, C C HC HC HC Cl), 131.8 (2C,
ar
ar
ar ar
ar
ar
ar
NCCCH), 132.9 (CH CC ), 141.2 (2C, NCCCH), 147.3
496 mg (85%); orange solid; mp 140 °C (dec); IR (KBr)
νmax 3431, 1934, 1718, 1629, 1550, 1511, 1474, 1409,
1372, 1308, 1224, 1200, 1159, 1080, 1026 cm ; H NMR
2
ar
19
(
NCCCH ), 147.8 (C Cl), 154.1 (2C, NCCH) ppm; F NMR
2 ar
11
−1 1
(
470 MHz, CD Cl ): δ = −146.1 to −146.8 (m) ppm;
B
2
2
NMR (160 MHz, CD Cl ): δ = −2.30 (t, J = 33.0 Hz) ppm;
(400 MHz, C D Cl , 80 °C, TMS): δ = 1.55–1.98 (m, 6H),
2
2
2
2
4
+
M (C H BClF N O) = 499.23 MS (CI, CH ) m/z (%):
2.27 (td, J = 2.7/10.9 Hz, 1H), 2.45 (m, 13H), 2.56–2.70
2
7
33
2
3
5
+
13
5
00.30 (26, [M+H] ), 480.20 (100), 482.20 (70), 462.20 (42);
HRMS (EI+): M calc. for C H BClF N O, 499.2368;
(m, 3H), 2.84–3.04 (m, 4H), 6.07 (s, 2H) ppm; C NMR
+
(100 MHz, C D Cl , 80 °C): δ = 14.7 (2C, NCCH ), 16.5
27
33
2
3
2
2
4
3
found: 499.2374; C H BClF N O (499.23) calc. C 64.88, H
(2C, CCCH3), 22.4 (NCH CH CH CHCH ), 26.2
27
33
2
3
2 2 2 2
6.65, N 8.41; found: C 64.66, H 6.71, N 8.34.
(CH CH CHCH ), 26.6 (CCH CH ), 28.4 (CCH ), 40.5
2 2 2 2 2 2
(
CHCO), 53.3 (NCH CH CH CHCH ), 55.5 (NCH CH),
2 2 2 2 2
1
0-{3-[3-(Ethoxycarbonyl)piperidine-1-yl]butyl}-5,5-
57.9 (CH NCH CH), 122.2 (2C, CCHC), 131.6 (2C,
2 2
4
4
difluoro-1,3,7,9-tetramethyl-5H-4 λ ,5 λ -dipyrrolo[1,2-c:
',1'-f][1,3,2]diazaborinin-4-ium-5-uide (8l) According to
CCCH ), 140.3 (2C, NCCCH ), 144.9 (NCCCH ), 154.7
3 2 2
1
9
2
(2C, NCCH ), 175.2 (CO) ppm; F NMR (475 MHz,
3
GP-3 (Method B): Compound 15b (815 mg, 1.77 mmol)
and ethyl piperidine-3-carboxylate (7l) (862 mg, 5.31 mmol,
CD Cl ): δ = −146.5 to −146.0 (m) ppm;
M
2
2
+
(C H BF N O ) = 417.24. MS (FAB , NBA) m/z (%):
2
2
30
2
3
2

Medicinal Chemistry Research
+
+
+
CDCl ): δ = −146.3 to −146.7 (m) ppm; 11B NMR
4
18.6 ([M+H] ); HRMS (FAB , NBA): [M+H] calc. for
3
C H BF N O , 418.2472; found: 418.2455.
(160 MHz, CDCl ): δ = −2.2 (t, J = 33.0 Hz) ppm; M
2
2
31
2
3
2
3
(
C H BF N O) = 389.25 MS (EI, 70 eV) m/z (%): 389.40
21 30 2 3
+
5
,5-Difluoro-1,3,7,9-tetramethyl-10-[4-(piperidin-1-yl)
(33, M ), 369.40 (33), 326.25 (19), 229.25 (27), 140.25
(19), 126.25 (49) 100.25 (100); HRMS (EI+): M calc. for
4
4
+
butyl]-5H-4 λ ,5 λ -dipyrrolo[1,2-c:2',1'-f][1,3,2]diazabori-
nin-4-ium-5-uide (9a) According to GP-3 (Method D):
Compound 16 (200 mg, 590 µmol) and piperidine (7a)
C H BF N O, 389.2445; found: 389.2456; C H BF
2
1
30
2
3
21 30
2
N O (389.25): calc. C 64.79, H 7.77, N 10.79; gef. C
3
(
1
70.3 mg, 826 µmol, 82.0 µL) as well as KI (246 mg,
.48 mmol) and K CO3 (245 mg, 1.77 mmol) in MeCN
64.74, H 7.91, N 10.67.
2
(
8
5.0 mL). Flash-SC (Gradient CH Cl → n-heptane/EtOAc
:1, 10% NEt3).
5,5-Difluoro-10-[4-(3-hydroxypiperidin-1-yl)butyl]-1,3,7,9-
2
2
4
4
tetramethyl-5H-4 λ ,5 λ -dipyrrolo[1,2-c:2',1'-f][1,3,2]diaza-
borinin-4-ium-5-uide (9c) According to GP-3 (Method
D): Compound 16 (200 mg, 590 µmol) and 3-
hydroxypiperidine (7c) (84.0 mg, 826 µmol) as well as KI
(246 mg, 1.48 mmol) and K CO (245 mg, 1.77 mmol) in
1
95 mg (86%); orange solid; mp 182–184 °C; DC: R =
f
0
2
1
1
1
2
.24 (n-heptane/EtOAc = 9:1, 10% NEt); IR (KBr) νmax 3427,
940, 2796, 2762, 1547, 1534, 1507, 1473, 1443, 1409, 1368,
338, 1305, 1267, 1253, 1224, 1202, 1161, 1134, 1099, 1060,
2
3
−1
1
025, 983 cm ; H NMR (500 MHz, CDCl , TMS): δ =
MeCN (5.0 mL). Flash-SC (n-heptane/EtOAc 8:1, 10%
3
.39–1.48 (m, 2H) 1.53–1.75 (m, 8H), 2.29–2.46 (m, 12H),
NEt ). The product was dissolved in EtOAc and extracted
3
.51 (s, 6H), 2.91–2.99 (m, 2H), 6.04 (s, 2H) ppm; 13C NMR
three times with buffer (pH = 2). The combined aqueous
(
100 MHz, CDCl , TMS): δ = 14.5 (2C, NCCCH ), 16.4 (2C,
phases were mixed with CHCl cooled to 0 °C and the pH
3
3
3
NCCH ), 24.5 (NCH CH CH CH CH ), 26.0 (2C, NCH
2
was adjusted to pH = 9 by adding buffer (pH = 10). The
3
2
2
2
2
2
CH CH CH CH ), 27.6 (CCH CH CH CH N), 28.2
aqueous layer was extracted with CHCl , dried over
2
2
2
2
2
2
2
2
3
(
CCH ), 29.7 (CCH CH ), 54.6, (2C, NCH CH CH CH
MgSO , filtered, and the solvent was removed.
2
2
2
2
2
2
2
4
CH ), 58.6 (CCH CH CH CH N), 121.6 (2C, CCHC),
96 mg (81%); orange solid; mp 169 °C; DC: R = 0.37 (n-
2
2
2
2
2
f
1
31.4 (2C, NCCCH2), 140.4 (2C, NCCCH), 146.4
heptane/EtOAc (8:1, 10% NEt ); IR (KBr) ν 3444, 2937,
2865, 2803, 2362, 2343, 1718, 1636, 1549, 1506, 1474,
3
max
19
(NCCCH ), 153.8 (2C, NCCH ) ppm; F NMR (500 MHz,
2
3
11
CDCl ,): δ = −146.21 to −146.90 (m) ppm;. B (160 MHz,
CDCl ): δ = −2.11 (t, J = 33.1 Hz) ppm; M (C H BF N )
=
1409, 1368, 1305, 1263, 1224, 1162, 10993 1079, 1059,
3
−
1
1
1027 cm ; H NMR (500 MHz, DMSO-D6, TMS): δ =
0.98–1.08 (m, 1H), 1.30–1.41 (m, 1H), 1.54–1.66 (m, 6H),
1.70–1.82 (m, 2H), 2.26–2.37 (m, 2H), 2.40 (s, 6H), 2.43 (s,
6H), 2.64 (d, J = 10.1 Hz, 1H), 2.82 (d, J = 10.4 Hz, 1H),
3
22 32
2 3
+
+
387.27 MS (CI, CH ) m/z (%): 388 (37, [M+H] ), 368
5
+
(100); HRMS (EI+): M calc. for C H BF N , 387.2652;
22
32
2 3
found: 387.2660.
2
.90–2.98 (m, 2H), 3.37–3.45 (m, 1H), 4.58 (d, J = 5.0 Hz,
1
3
5
4
,5-Difluor-1,3,7,9-tetramethyl-10-(4-morpholinobutyl)-5H-
λ ,5 λ -dipyrrolo[1,2-c:2',1'-f][1,3,2]diazaborinin-4-ium-5-
1H), 6.23 (s, 2H) ppm; C NMR (125 MHz, DMSO-D6,
4
4
TMS): δ = 14.0 (2C, H CCN), 15.7 (2C, H CCC), 23.1
3
3
uide (9b) According to GP-3 (Method D): Compound 16
200 mg, 590 μmol) and morpholine (7b) (72.0 mg,
26 μmol) as well as KI (246 mg, 1.48 mmol) and K CO
(NCH CH), 26.5 (CCH CH CH CH N), 27.3 (CCH CH
CH CH N), 28.7 (CCH CH CH CH N), 33.3 (NCH CH
2 2 2 2 2 2 2
CH CH), 52.9 (NCH CH CH CH), 56.5 (CCH CH CH
2 2 2 2 2 2
2 2 2 2 2 2
2
2
2
(
8
2
3
(
245 mg, 1.77 mmol) in MeCN (5.0 mL). Flash-SC (n-
heptan/EtOAc 6:3, 10% NEt3).
79 mg (78%); orange solid; mp 172–173 °C; DC: R =
CH N), 61.2 (NCH CH CH CH), 66.0 (NCH CH), 121.5
2 2 2 2 2
(2C, CCHC), 130.6 (2C, CCC), 140.8 (2C, H CCC), 146.8
3
1
9
1
(NCCCH2), 152.9 (2C, H CCN) ppm;
(470 MHz, DMSO-D6): δ = −143.4 to −144.2 ppm;
F NMR:
f
3
1
1
0
3
2
1
1
.26 (n-heptane/EtOAc 6:3, 10% NEt ); IR (KBr) ν
B
3
max
449, 2963, 2944, 2918, 1886, 1855, 1818, 1796, 1766,
367, 2344, 1734, 1645, 1547, 1507, 1474, 1457, 1408,
366, 1338, 1305, 1283, 1260, 1201, 1161, 1120, 1096,
NMR: (160 MHz, DMSO-D6): δ = −2.2 (t, J = 32.9 Hz)
ppm; M (C H BF N O) = 403.26 MS (EI, 70 eV) m/z
2
2
32
2
3
+
(%): 403.25 (31, M ), 383.25 (21), 114.25 (100); HRMS
−
1
1
(EI+): M+ calc. for C H BF N O, 403.2601; found:
077, 1057, 1206 cm ; H NMR (400 MHz, CD Cl ,
2
2
22 32
2
3
TMS): δ = 1.58–1.78 (m, 4H), 2.33–2.41 (m, 6H), 2.44 (s,
403.2597.
6
4
H), 2.46 (s, 6H), 2.92–3.02 (m, 2H), 3.64 (t, J = 4.6 Hz,
H), 6.09 (s, 2H) ppm; 13C NMR (125 MHz, CD Cl ,
5,5-Difluoro-10-[4-(4-hydroxypiperidin-1-yl)butyl]-1,3,7,9-tet-
2
2
4
4
TMS): δ = 14.6 (2C, H CCC), 16.6 (2C, H CCN), 27.2,
ramethyl-5H-4 λ ,5 λ -dipyrrolo[1,2-c:2′,1′-f][1,3,2]diazabor-
inin-4-ium-5-uide (9d) According to GP-3 (Method D):
Compound 16 (200 mg, 590 µmol) and 4-hydroxypiperidine
(7d) (84.0 mg, 826 µmol), as well as KI (246 mg, 1.48 mmol)
and K CO (245 mg, 1.77 mmol) in MeCN (5.0 mL). Flash-
3
3
(
(
(
CCH CH CH CH N), 28.5 (CCH CH CH ), 29.6
2 2 2 2 2 2 2
CCH CH CH CH N), 54.1 (2C, NCH CH O) 58.2
2
2
2
2
2
2
CCH CH CH CH N), 67.3 (2C, NCH CH O), 121.9 (2C,
2
2
2
2
2
2
CH), 131.8 (2C, CCC), 141.2 (2C, H CCCC), 147.2
3
2
3
19
(
CH CC), 154.1 (2C, H CCN) ppm; F NMR (470 MHz,
SC (EtOAc, 10% NEt3).
2
3

Medicinal Chemistry Research
+
1
76 mg (74%); orange solid; mp 140 °C (dec); DC: R =
464.3042 [M+H] ; C H BF N (389.25): calc. C 72.57,
28 36 2 3
f
0
2
1
.24 (EtOAc, 10% NEt ); IR (KBr) ν 3429, 2931, 2805,
H 7.83 N 9.07; found: C 72.43, H 7.74, N 9.10.
3
max
363, 2344, 1636, 1550, 1510, 1473, 1410, 1367, 1308,
−
1
1
224, 1201, 1160, 1108, 1078, 1026 cm ; H NMR
5,5-Difluor-1,3,7,9-tetramethyl-10-{4-[4-phenyl-5,6-dihy-
4
4
(
500 MHz, DMSO-D6, TMS): δ = 1.29–1.39 (m, 2H),
dropyridin-1(2H)-yl]butyl}-5H-4 λ ,5 λ -dipyrrolo[1,2-c:
2′,1′-f][1,3,2]diazaborinin-4-ium-5-uid (9f) According to
GP-3 (Method D): Compound 16 (488 mg, 1.44 mmol)
and 4-phenyl-1,2,3,6-tetrahydropyridine (7f) (321 mg,
2.02 mmol), as well as KI (598 mg, 3.60 mmol) and
K CO (597 mg, 4.32 mmol) in MeCN (5.0 mL). Flash-SC
1
2
2
.52–1.65 (m, 4H), 1.69 (d, J = 9.8 Hz, 2H), 1.95 (s, 2H),
.26–2.38 (m, 2H), 2.40 (s, 6H), 2.43 (s, 6H), 2.67 (s, 2H),
.88–2.97 (m, 2H), 3.41 (s, 1H), 4.55 (s, 1H), 6.23 (s, 2H)
1
3
ppm; C NMR (100 MHz, DMSO-D6, TMS): δ = 14.0
(
2C, H CCN), 15.7 (2C, H CCC) 26.6 (CCH CH ), 27.3
3 3 2 2
2
3
(
CCH ), 28.7 (CCH CH CH ), 34.3 (2C, NCH CH CH),
(1. tBuOMe/pentane 7:3, 2% NEtMe 2. tBuOMe/pentane
2
2
2
2
2
2
2
5
0.9 (2C, NCH CH CH), 56.3 (CH NCH CH CH) 66.3
7:3 → tBuOMe/pentane 7:3, 3% NEtMe2).
2
2
2
2
2
(
NCH CH CH), 121.5 (2C, CCHC), 130.6 (2C,
268 mg (40%); orange solid; mp 185–187 °C; DC: R =
2
2
f
NCCCH ), 140.8 (2C, H CCC), 146.9 (NCCCH ), 152.9
0.25 (tBuOMe/pentane 7:3, 3% NEtMe ); IR (KBr) ν
2
3
2
2
max
19
(
2C H CCN) ppm; F NMR (470 MHz, CDCl ): δ =
3433, 2919, 2867, 1551, 1509, 1467, 1306, 1203, 1077,
3
3
1
1
−1 1
−
143.7 to −144.0 ppm; B NMR (160 MHz, CDCl3):
1060, 984, 813, 749, 714, 694 cm ; H NMR (400 MHz,
δ = −2.2 (t, J = 32.9 Hz) ppm; M (C H BF N O) =
CD Cl ): δ = 1.57–1.68 (m, 4H), 2.36 (s, 6H), 2.37 (s, 6H),
2.38–2.48 (m, 4H), 2.58 (t, J = 5.6 Hz, 2H), 2.88–2.95 (m,
2
2
32
2
3
2
2
+
4
03.26 MS (EI, 70 eV) m/z (%): 403.40 (49, M ), 383.40
(
16), 269.25 (12), 154.25 (13), 140.25 (45), 114.25 (100);
2H), 3.02 (q, J = 3.0 Hz, 2H), 5.97–6.01 (m, 3H), 7.10–7.17
+
13
HRMS (EI+): M calc. for C H BF N O, 403.2601;
(m, 1H), 7.19–7.26 (m, 2H), 7.27–7.34 (m, 2H) ppm;
C
2
2
32
2
3
found: 403.2627.
NMR (101 MHz, CD Cl ): δ = 14.2 (t, J = 2.6 Hz, H CCN),
2 2 3
1
6.1 (H CCCN), 27.6 (CCH CH CH CH N), 28.1 (NCH
3 2 2 2 2 2
5
,5-Difluoro-1,3,7,9-tetramethyl-10-[4-(4-phenylpiperidin-1-
CH C), 28.2 (CCH CH CH CH N), 29.4 (CCH CH CH
2 2 2 2 2 2 2 2
CH N), 50.3 (NCH CH C), 53.3 (NCH CH), 57.2 (CCH
2 2 2 2 2
4
4
yl)butyl]-5H-4 λ ,5 λ -dipyrrolo[1,2-c:2',1'-f][1,3,2]diazabor-
inin-4-ium-5-uide (9e): According to GP-3 (Method D):
Compound 16 (200 mg, 590 µmol) and 4-phenylpiperidine
CH CH CH N), 121.5 (2C, CCHC), 122.0 (NCH CH),
2
2
2
2
124.7 (2C, CC C H), 126.9 (C C HC HC H), 128.2
ar ar
ar ar
ar
ar
(
7e) (137 mg, 826 µmol) as well as KI (246 mg, 1.48 mmol)
(2C, CC HC HC H), 131.4 (2C, NCCCH2), 134.8
ar ar ar
and K CO (245 mg, 1.77 mmol) in MeCN (5.0 mL). Flash-
(NCH CH C), 140.9 (2C, H CCCN), 146.9 (2C, CC ,
2
3
2
2
3
ar
1
9
SC (1.n-heptan/EtOAc 7:2, 10% NEt 2. Gradient: n-hep-
NCCCH ), 153.6 (2C, H CCN). ppm; F NMR (470 MHz,
2 3
3
1
1
tane/EtOAc 7:2→ n-heptane/EtOAc 7:2, 10% NEt3).
CD Cl ): δ = −146.7 to −146.4 (m) ppm; B NMR
2 2
2
35 mg (86%); orange solid; mp 167 °C; DC: R = 0.3 (n-
(160 MHz, CD Cl ): δ = 0.52 (t, J = 33.1 Hz) ppm; HRMS
2 2
f
heptane/Ethylacetat (7:2, 10% NEt ); IR (KBr) ν
3425,
(ESI): [M+H]+ calc. for C H BF N , 462. 2887; found:
3
max
28 35 2 3
3
1
1
020, 2965, 2927, 2862, 2907, 2770, 2742, 1550, 1507,
475, 1446, 1410, 1376, 1367, 1310, 1256, 1225, 1202,
159, 1101, 1074, 1066, 1028 cm ; H NMR (400 MHz,
462.2890.
5,5-Difluoro-10-[4-(4-hydroxy-4-phenylpiperidin-1-yl)butyl]-
−
1 1
4
4
CD Cl , TMS): δ = 1.55–1.76 (m, 6H), 1.76–1.86 (m, 2H),
2
2
CCHC), 7.15–7.20 (m, 1H), 7.20–7.25 (m, 2H),
7
1,3,7,9-tetramethyl-5H-4 λ ,5 λ -dipyrrolo[1,2-c:2',1'-f][1,3,2]
diazaborinin-4-ium-5-uide (9g) According to GP-3
(Method D): Compound 16 (200 mg, 590 µmol) and 4-
hydroxy-4-phenylpiperidine (7g) (146 mg, 826 µmol) as
well as KI (246 mg, 1.48 mmol) and K CO (245 mg,
2
2
.00 (td, J = 2.5/11.7 Hz, 2H), 2.36–2.43 (m, 2H),
.43–2.55 (m 13H), 2.91–3.05 (m, 4H), 6.09 (s, 2H
13
.26–7.32 (m, 2H) ppm; C NMR (125 MHz, CD Cl ,
2 2
2
3
TMS): δ = 14.6 (2C, NCCH ), 16.6 (2C, NCCCH ), 27.9
1.77 mmol) in MeCN (5.0 mL). Flash-SC (n-heptane/
EtOAc 6:3, 10% NEt3).
3
3
(
(
(
CCH CH CH CH N), 28.6 (CCH CH CH CH N), 29.8
2 2 2 2 2 2 2 2
CCH CH CH CH N), 34.0 (2C, NCH CH CH), 43.2
222 mg (78%); orange solid; mp 184–186 °C; DC: R =
2
2
2
2
2
2
f
NCH CH CH), 54.8 (2C, NCH CH CH), 58.2 (CH
0.27 (n-heptane/EtOAc = 6:3, 10% NEt ); IR (KBr) ν
2
2
2
2
2
3
max
NCH CH CH), 121.9 (2C, CCHC), 126.4 (CC C HC H-
3556, 2478, 2953, 2925, 2794, 2769, 1551, 1511, 1473,
2
2
ar ar
ar
C H), 127.2 (2C, CC C HC HC H), 128.7 (2C, CC
ar-
1467, 1445, 1410, 1368, 1307, 1269, 1255, 1202, 1158,
ar
ar ar
ar
ar
−
1 1
C HC HC H), 131.8 (2C, NCCCH2), 141.3 (2C,
1129, 1108, 1079, 1046, 1025 cm ; H NMR (500 MHz,
DMSO-D6; TMS): δ = 1.55–1.71 (m, 6H), 1.88 (td, J =
4.3/13.0 Hz, 2H), 2.31–2.43 (m, 10H), 2.46 (s, 6H), 2.65
(d, J = 10.2 Hz, 2H), 2.99 (m, 2H), 4.77 (s, 1H), 6.25 (s,
2H), 7.20 (t, J = 7.3 Hz, 1H), 7.31 (t, J = 7.7 Hz, 2H),
ar
ar
ar
NCCCH ), 147.2 (NCCCH ), 147.4 (CC ), 154.0 (2C,
3
2
ar
1
9
NCCH ) ppm; F NMR (470 MHz, CD Cl ): δ = −145.0
to −148.5 (m) ppm; B NMR (160 MHz, CD Cl ): δ =
3
2
2
11
2
2
−
0.45 (t, J = 32.9 Hz) ppm; M (C H BF N ) = 463.29
28
36
2
3
+
13
MS (ESI+) m/z (%): 464.30 (100, [M+H] ); HRMS
7.45–7.49 (m, 2H) ppm; C NMR (125 MHz, DMSO-
+
(
ESI+): [M+H] calc. for C H BF N , 464.3043; found:
D6): δ = 14.1 (2C, H CCN), 15.8 (2C, H CCCN), 26.7
28
37
2
3
3
3

Medicinal Chemistry Research
(
CCH CH CH CH N), 27.5 (NCCCH ), 29.0 (CCH CH
GP-3 (Method D): Compound 16 (100 mg, 295 µmol) and
4-(4-methoxyphenyl)piperidin-4-ol (7i) (86.0 mg, 413 µmol)
as well as KI (122 mg, 737 µmol) and K CO (122 mg,
2
2
2
2
2
2
2
2
CH CH N), 38.1 (2C, NCH CH C), 49.1 (2C, NCH
CH C), 56.8 (CCH CH CH CH N), 69.7 (NCH CH C),
2
2
2
2
2
2
2
2
2
2
2
2
3
1
21.7 (2C, CCHC), 124.8 (2C, CC C H), 126.2 (C
885 µmol) in MeCN (2.5 mL). Flash-SC (n-heptane/EtOAc
5:4, 10% NEt3).
ar ar
ar-
C HC HC H), 127.9 (2C, CC HC HC H), 130.8 (2C,
ar
ar
ar
ar
ar
ar
NCCCH ), 140.9 (2C, H CCCN), 147.1 (NCCCH ), 150.3
115 mg (74%); orange solid; mp 190 °C; DC: R = 0.27
2
3
2
f
1
9
(
CC ), 153.0 (2C, H CCN) ppm; F NMR (470 MHz,
(EtOAc/n-heptane 5:4, 10% NEt ); IR (KBr) ν
3440,
ar
3
3
max
11
DMSO): δ = −143.7 to −143.9 (m) ppm; B NMR
160 MHz, DMSO): δ = −2.3 (t, J = 32.6 Hz) ppm; M
C H BF N O) = 479.29 MS (EI, 70 eV) m/z (%): 479.50
3411, 2988, 2945, 2924, 2865, 2804, 2769, 2366, 2345,
1609, 1546, 1508, 1471, 1458, 1443, 1411, 1375, 1366,
1341, 1304, 1266, 1255, 1201, 1162, 1134, 1103, 1059,
(
(
28
36
+
2 3
−1
1
(
30, M ), 269.25 (10), 229.15 (15), 216.25 (21), 190.25 (42),
72.25 (17), 83.00 (100); HRMS (EI+): M calc. for
C H BF N O, 479.2914; found: 479.2916.
1028 cm ; H NMR (500 MHz, CD Cl , TMS): δ =
2 2
1
1.68–1.75 (m, 6H,), 2.04 (td, J = 4.4/13.2 Hz, 2H), 2.38
(t, J = 10.9 Hz, 2H), 2.42–2.50 (m, 14H), 2.74 (d, J =
28
36
2 3
1
1.2 Hz, 2H), 2.96–3.06 (m, 2H), 3.78 (s, 3H), 6.09 (s, 2H),
1
3
5
1
,5-Difluoro-10-{4-[4-hydroxy-4-(2-methoxyphenyl)piperidin-
-yl]butyl}-1,3,7,9-tetramethyl-5H-4 λ ,5 λ -dipyrrolo[1,2-
6.85–6.89 (m, 2H), 7.39–7.43 (m, 2H) ppm; C NMR
(125 MHz, CD Cl , TMS): δ = 14.6 (2C, NCCCH ), 16.6
4
4
2
2
3
c:2',1'-f][1,3,2]diazaborinin-4-ium-5-uide (9h) According to
GP-3 (Method D): Compound 16 (100 mg, 295 µmol) and
(2C, NCCH3), 27.9 (CCH CH CH CH N), 28.6
2 2 2 2
(CCH CH CH CH N), 29.8 (CCH CH CH CH N), 39.0
2
2
2
2
2
2
2
2
4
-(2-methoxyphenyl)piperidin-4-ol (7h) (86.0 mg, 413 µmol)
(2C, NCH CH C), 50.0 (2C, NCH CH C), 55.6 (H CO),
2 2 2 2 3
as well as KI (122 mg, 737 µmol) and K CO (122 mg,
58.0 (CCH CH CH CH N), 71.2 (NCH CH C), 113.8
2
3
2
2
2
2
2
2
8
85 µmol) in MeCN (2.5 mL). Flash-SC (1. n-heptane/
(C C HC HC O), 121.9 (CCHC), 126.2 (C C HC H-
ar ar ar ar ar ar ar
EtOAc 5:4, 10% NEt , 2. Gradient: n-heptane/EtOAc 5:4 →
C O), 131.8 (NCC), 141.3 (3C, H CCC und CH CC
ar 3 2 ar-
3
n-heptane/EtOAc 5:4, 10% NEt3).
C H), 147.4 (CCCCH ), 154.0 (2C, NCCH ), 159.0
ar 2 3
1
9
1
21 mg (81%); orange solid; mp 174–175 °C; DC: R =
(H CO) ppm; F NMR (470 MHz, CD Cl ): δ = −143.4
f
3
2
2
1
1
0
3
1
.27 (n-heptane/EtOAc 5:4, 10% NEt ); IR (KBr) ν
548, 3425, 2934, 2807, 2360, 2343, 16545, 1637, 1629,
551, 1533, 1509, 1488, 1466, 1466, 1407, 1370, 1307,
to −146.7 (m) ppm; B NMR (160 MHz, CD Cl ): δ =
2 2
3
max
−2.14 (t, J = 33.0 Hz) ppm; M (C H BF N O ) = 509.30
29 38 2 3 2
+
MS (FAB, NBA) m/z: 510.5 ([M+H] ); HRMS (FAB,
−1
+
1
260, 1232, 1208, 1159, 1137, 1097, 1080, 1042, 1023 cm ;
NBA): [M+H] . calc. for C H BF N O , 510.3098;
2
9
39
2
3
2
1
H NMR (500 MHz, DMSO-D6, TMS): δ = 1.37 (d, J =
found: 510.3124.
1
(
(
3.2 Hz, 2H), 1.59–1.74 (m, 4H), 2.25–2.49 (m, 16H), 2.62
d, J = 9.6 Hz, 2H), 2.96–3.04 (m, 2H), 3.76 (s, 3H), 4.62
s, 1H), 6.26 (s, 2H), 6.92 (t, J = 7.5 Hz, 1H), 6.96 (d, J =
10-{4-[4-(2-Chlorophenyl)-4-hydroxypiperidin-1-yl]butyl}-
4
4
5,5-difluoro-1,3,7,9-tetramethyl-5H-4 λ ,5 λ -dipyrrolo[1,2-
c:2',1'-f][1,3,2]diazaborinin-4-ium-5-uide (9j) According to
GP-3 (Method D): Compound 16 (200 mg, 590 µmol) and
4-(2-chlorophenyl)piperidin-4-ol (7j) (175 mg, 826 µmol) as
well as KI (245 mg, 1.48 mmol) and K CO (245 mg,
8
1
.2 Hz, 1H), 7.20 (td, J = 8.1/1.7 Hz, 1H), 7.57 (dd, J = 7.7/
.7 Hz, 1H) ppm; C NMR (125 MHz, DMSO-D6, TMS):
1
3
δ = 14.0 (2C, H CCN), 15.7 (2C, H CCC), 26.5
3
3
(
CCH CH CH CH N), 27.3 (CCH CH CH CH N), 28.8
2 2 2 2 2 2 2 2
2
3
(
CCH CH CH CH N), 34.6, (2C, NCH CH C) 49.0 (2C,
1.77 mmol) in MeCN (5.0 mL). Flash-SC (1. n-heptane/
2
2
2
2
2
2
NCH CH C), 55.1 (H CO), 56.5 (CCH CH CH CH N),
EtOAc 4:5, 10% NEt , 2. Gradient: n-heptane/EtOAc 4:5 →
2
2
3
2
2
2
2
3
7
0.1 (CH CC ), 115.5 (C C HC HC HC HC ), 120.0
n-heptane/EtOAc 4:5, 10% NEt3).
2
ar
ar ar
ar
ar
ar
ar
(
C C HC HC HC HC ), 121.5 (2C, CCHC), 126.4
276 mg (91%); orange solid; mp 218–219 °C; DC: R =
ar ar
ar
ar
ar
ar
f
(
C C HC HC HC HC ), 127.6 (C C HC HC HC H-
0.37 (EtOAc/n-heptane 5:4, 10% NEt ); IR (KBr) ν
ar ar
ar
ar
ar
ar
ar ar
ar
ar
ar
3
max
C ), 130.6 (NCCCH ), 136.7 (CC C H), 140.9 (2C,
3553, 3537, 3442, 2926, 2861, 2820, 1550, 1508, 1469,
ar
2
ar ar
NCCCH ), 147.0 (2C, NCCCH ), 152.9 (2C, H CCN),
1433, 1407, 1372, 1307, 1262, 1225, 1204, 1158, 1107,
3
3
3
19
−1 1
1
56.2 (C OCH ) ppm; F NMR: (470 MHz, DMSO-D6):
1079, 1063, 1039 cm ; H NMR (500 MHz, DMSO-D6,
TMS): δ = 1.49 (d, J = 12.3 Hz, 2H), 1.66 (s, 4H),
2.32–2.42 (m, 10H) 2.47 (s, 6H), 2.57 (td, J = 4.0/
12.8 Hz, 2H), 2.67 (d, J = 9.9 Hz, 2H), 2.95–3.04 (m,
2H), 4.99 (s, 1H), 6.24 (s, 2H), 7.25 (td, J = 7.6/1.7 Hz,
1H), 7.32 (dd, J = 1.3/7.8 Hz, 1H), 7.34–7.38 (m, 1H), 7.82
ar
3
11
δ = −143.6 to −144.0 ppm; B NMR: (160 MHz, DMSO-
D6): δ = −2.1 (t, J = 32.9 Hz) ppm; M (C H BF N O ) =
2
9
38
2
3
2
+
5
(
09.30 MS (FAB, NBA) m/z: 510.5 ([M+H] ); HRMS
FAB, NBA): [M+H]+ calc. for C H BF N O ,
29
39
2
3
2
5
10.3098; found: 510.3108.
1
3
(dd, J = 1.6/8.0 Hz, 1H) ppm;
C NMR (125 MHz,
5
1
2
,5-Difluoro-10-{4-[4-hydroxy-4-(4-methoxyphenyl)piperidin-
-yl]butyl}-1,3,7,9-tetramethyl-5H-4 λ ,5 λ -dipyrrolo[1,2-c:
',1'-f][1,3,2]diazaborinin-4-ium-5-uide (9i) According to
DMSO-D6): δ = 14.1 (2C, NCCH ), 15.8 (2C, NCCCH ),
3
3
4
4
26.7 (NCCCH CH ), 27.5 (NCCCH ), 28.9 (CCH CH
2 2 2 2
2
2
CH CH N), 34.1 (2C, NCH CH C), 49.0 (2C, NCH
2
2
2
2

Medicinal Chemistry Research
CH C), 56.6 (CCH CH CH CH N), 70.8 (NCH CH C),
heptane/EtOAc 8:1, 10% NEt , 2. Gradient: n-heptane/
2
2
2
2
2
2
2
3
1
21.6 (2C, CCHC), 127.0 (CC C C H), 128.3 (2C,
EtOAc 8:1 → n-heptane/EtOAc 8:1, 10% NEt3).
ar ar ar
CC C HC HC HC H), 128.3 (CC C HC HC HC H),
327 mg (80%); orange solid; mp 109 °C; DC: R = 0.2 (n-
ar ar
ar
ar
ar
ar ar
ar
ar
ar
f
1
30.5 (CC C ), 130.7 (2C, NCCCH2), 131.3 (CC HC H-
heptane/EtOAc 8:1, 10% NEt ); IR (KBr) ν 3383, 2934,
ar ar
ar
ar
3
max
C H), 140.9 (2C, NCCCH ), 145.6 (CC ), 147.1 (NCCCH ),
2865, 2806, 1730, 1550, 1511, 1470, 1410, 1371, 1309,
1263, 1224, 1202, 1158, 1078, 1029, 986 cm ; H NMR:
ar
3
1
ar
2
9
−1 1
1
53.0 (2C, NCCH ) ppm; F NMR (470 MHz, DMSO-D6):
3
11
δ = −144.2 to −143.3 (m) ppm; B NMR (160 MHz,
DMSO-D6): δ = −0.55 (t, J = 32.8 Hz) ppm; M (C H
(500 MHz, CD Cl , TMS): δ = 1.21 (t, J = 7.1, 3H),
2
2
1.36–1.57 (m, 2H), 1.57–1.75 (m, 5H), 1.84–1.92 (m,
1H), 1.97 (t, J = 10.7, 1H), 2.12 (t, J = 10.8, 1H),
2.35–2.40 (m, 2H), 2.40–2.48 (m, 13H), 2.70 (d, J =
11.1 Hz, 1H), 2.91 (d, J = 11.2, 1H), 2.93–2.99 (m, 2H),
2
8 35
BClF N O) = 513.25 MS (EI, 70 eV) m/z (%): 513.4
2
3
+
+
(
12, M ), 189.01 (100); HRMS (EI+): M calc. for
C H BClF N O, 513.2524; found: 513.2524.
2
8
35
2 3
1
3
4
.07 (qd, J = 2.8/7.1 Hz, 2H), 6.08 (s, 2H) ppm; C NMR
1
5
0-{4-[4-(4-Chlorophenyl)-4-hydroxypiperidin-1-yl]butyl}-
,5-difluoro-1,3,7,9-tetramethyl-5H-4 λ ,5 λ -dipyrrolo[1,2-
(125 MHz, CD Cl , TMS): δ = 14.4 (OCH CH ), 14.6 (2C,
NCCH ), 16.6 (2C, NCCCH ), 25.1 (CH CH CH), 27.4
3 3 2 2
2
2
2
3
4
4
c:2',1'-f][1,3,2]diazaborinin-4-ium-5-uide (9k) According to
GP-3 (Method D): Compound 16 (100 mg, 295 µmol) and
(NCH CH CH CH), 27.7 (NCH CH CH CH C), 28.6
2 2 2 2 2 2 2
(NCH CH CH CH C), 29.8 (NCH CH CH CH C), 42.4
2
2
2
2
2
2
2
2
4
-(4-chlorophenyl)piperidin-4-ol (7k) (87.0 mg, 413 µmol)
(NCH CH CH CH), 53.4 (NCH CH CH CH), 55.9
2 2 2 2 2 2
as well as KI (122 mg, 737 µmol) and K CO (122 mg,
(NCHCH ), 58.1 (NCH CH CH CH C), 60.6 (OCH CH ),
2
3
2
2
2
2
2
2
3
8
85 µmol) in MeCN (2.5 mL). Flash-SC (n-heptane/EtOAc
121.9 (2C, CCHC), 131.8 (2C, NCCCH ), 141.3 (2C,
3
5
:4, 10% NEt3).
NCCCH ), 147.4 (NCCCH ), 154.0 (2C, NCCH ), 174.4
3
2
3
1
9
124 mg (82%); orange solid; mp 218–219 °C; DC: R =
(CO) ppm; F NMR (470 MHz, CD Cl ): δ = −146.3 to
f
2 2
1
1
0
3
1
1
.37 (EtOAc/n-heptane 5:4, 10% NEt ); IR (KBr) ν
573, 3425, 2947, 2923, 2820 2362, 2345 1637, 1549,
=
−146.7 (m) ppm; B NMR (160 MHz, CD Cl ): δ = −0.5
2 2
3
max
(t, J = 32.9 Hz) ppm; M (C H BF N O ) = 459.29 MS
2
5
36
2
3
2
+
+
507, 1481, 1405, 1370, 1348, 1307, 1244, 1203, 1160,
(CI, CH ) m/z (%): 460 (44, [M+H] ), 440 (100); HRMS
5
−
1
1
+
130 1083 cm ; H NMR (500 MHz, DMSO-D6, TMS):
(EI+): M calc. for C H BF N O , 459.2869; found:
2
5
36
2
3
2
δ = 1.57 (d, J = 12.0 Hz, 2H), 1.60–1.69 (m, 4H), 1.86 (td,
J = 4.1/12.9 Hz, 2H), 2.34 (t, J = 10.7 Hz, 2H), 2.38–2.41
459.2872.
(
(
(
m, 8 H), 2.46 (s, 6H), 2.64 (d, J = 10.8 Hz, 2H), 2.94–3.02
10-[4-(3-Carboxypiperidine-1-yl)butyl]-5,5-difluoro-1,3,7,9-
4
4
m, 2H), 4.89 (s, 1H), 6.25 (s, 2H), 7.34–7.38 (m, 2H), 7.48
tetramethyl-5H-4 λ ,5 λ -dipyrrolo[1,2-c:2',1'-f][1,3,2]diaza-
borinin-4-ium-5-uide (9m) According to GP-2: Compound
9l (322 mg, 0.70 mmol) in 10.0 mL solvent mixture
(CH CL /MeOH, 2:1) and LiOH (42.0 mg, 1.75 mmol)
13
d, J = 8.6 Hz, 2H) ppm; C NMR (100 MHz, DMSO-D6,
TMS): δ = 14.0 (2C, H CCCN), 15.7 (2C, H CCN), 26.6
3
3
(
CCH CH CH CH N), 27.4 (CCH CH CH CH N), 28.8
2 2 2 2 2 2 2 2
2
2
(
CCH CH CH CH N), 37.8 (2C, NCH CH C), 48.9 (2C,
solved in H O (1.8 mL). The reaction mixture was stirred
2
2
2
2
2
2
2
NCH CH C), 56.7 (CCH CH CH CH N), 69.4 (NCH
2
for 4 d.
2
2
2
2
2
2
CH C), 121.6 (2C, CCHC), 126.7 (2C, C C HC HC Cl),
214 mg (71%); orange solid; mp 119 °C; IR (KBr): ev =
2
ar ar
ar
ar
1
27.6 (2C, C C HC HC Cl), 130.6 (C C HC HC Cl
ar ar ar ar ar ar ar ar
3432, 2932, 2868, 1708, 1550, 1511, 1474, 1408, 1371,
1308, 1265, 1224, 1200, 1159, 1080, 1026 cm ; H NMR
−
1 1
und NCCCH ), 140.8 (2C, H CCCN), 146.9 (2C, CHCCC),
2
3
19
1
49.1 (C Cl), 152.9 (2C, H CCN) ppm;
F NMR
(400 MHz, C D Cl , 40 °C, TMS): δ = 1.50–1.92 (m, 8H),
ar
3
2
2
4
1
1
(
470 MHz, DMSO): δ = −143.7 to −143.9 (m) ppm;
B
1.97 (d, J = 12.4 Hz, 1H), 2.27–2.36 (m, 1H), 2.41 (s, 6H),
2.49 (s, 6H), 2.56 (t, J = 7.5 Hz, 2H), 2.67 (s, 1H),
2.90–3.04 (m, 3H), 3.11 (d, J = 12.7 Hz, 1H), 6.08 (s,
NMR (160 MHz, DMSO): δ = −2.3 (t, J = 32.2 Hz) ppm;
M (C H BF ClN O) = 513.25 MS (EI, 70 eV) m/z (%):
2
8
35
2
3
+
13
5
(
13.4 (2, M ), 296.4 (11), 295.40 (51), 157.25 (12), 170.25
54), 156.25 (100); HRMS (EI+):
2H) ppm; C NMR (100 MHz, C D Cl , 40 °C): δ = 14.8
2
2
4
+
M
calc. for
(2C, CCCH3), 16.6 (2C, NCCH3), 22.0 (NCH2
C H BF ClN O, 513.2524; found: 513.2513.
CH CH CH), 26.4 (NCH CH CH CH), 26.5 (CCH CH ),
2
8
35
2
3
2
2
2
2
2
2
2
2
8.1 (CCH ), 29.6 (CCH CH CH ), 40.2 (CHCO), 53.5
2 2 2 2
1
0-{4-[3-(Ethoxycarbonyl)piperidine-1-yl]butyl}-5,5-
(NCH CH CH CH), 55.2 (NCH CH), 57.3 (CH NCH CH),
2 2 2 2 2 2
4
4
difluoro-1,3,7,9-tetramethyl-5H-4 λ ,5 λ -dipyrrolo[1,2-c:
',1'-f][1,3,2]diazaborinin-4-ium-5-uide (9l) According to
122.1 (2C, CCHC), 131.5 (2C, NCCCH ), 140.6 (2C,
3
2
NCCCH ), 145.5 (NCCCH ), 154.5 (2C, NCCH ), 176.4
2
2
3
1
9
GP-3 (Method D): Compound 16 (300 mg, 885 µmol) and
ethyl piperidine-3-carboxylate (7l) (201 mg, 1.24 mmol,
(CO) ppm; F NMR (375 MHz, C D Cl ): δ = −145.1 to
−145.9 (m) ppm; B NMR (128 MHz, C D Cl ): δ = 0.5
2 2 4
1
1
2
2
4
0
.2 mL) as well as KI (367 mg, 2.21 mmol) and K CO
(t, J = 33. Hz) ppm; M (C H BF N O ) = 431.25 MS
(FAB , NBA) m/z (%): 432.3 ([M+H] ); HRMS (FAB ,
2
3
23 32
2
3
+
2
+
+
(
367 mg, 2.65 mmol) in MeCN (7.5 mL). Flash-SC (1. n-

Medicinal Chemistry Research
NBA): [M+H]+ calc. for C H BF N O , 432.2628;
found: 432.2623.
NCCH ) ppm; F NMR (470 MHz, CD Cl ): δ = −146.2
19
23
33
2
3
2
3
2
2
1
1
to −147.0 (m) ppm; B NMR (160 MHz, CD Cl ): δ =
2 2
−
0.5 (t, J = 33.0 Hz) ppm; M (C H BF N O) = 403.26.
22 32 2 3
+
5
,5-Difluoro-1,3,7,9-tetramethyl-10-[5-(piperidin-1-yl)pen-
MS (DIE+) m/z (%): 403.49 (36.06, M ), 670.50 (100);
4
4
HRMS (DEI+): M+ calc. for C H BF N O, 403.2601;
tyl]-5H-4 λ ,5 λ -dipyrrolo[1,2-c:2',1'-f][1,3,2]diazaborinin-4-
ium-5-uide (10a) According to GP-3 (Method C): Com-
pound 17 (117 mg, 295 µmol) and piperidine (7a) (35.0 mg,
2
2
32
2
3
found: 403.2600.
4
13 µmol, 42.0 µL) and K CO (122 mg, 855 µmol) in
2 3
5,5-Difluoro-10-[5-(3-hydroxypiperidin-1-yl)pentyl]-1,3,7,9-
4
4
MeCN (2.5 mL). Flash-SC (n-heptane/EtOAc 8:1, 10%
NEt3).
tetramethyl-5H-4 λ ,5 λ -dipyrrolo[1,2-c:2',1'-f][1,3,2]diaza-
borinin-4-ium-5-uide (10c) According to GP-3 (Method
C): Compound 17 (117 mg, 295 µmol) and 3-
9
3.2 mg (78%); orange solid; Mp 103–104 °C; DC: R =
f
0
2
1
1
.2 (n-heptane/EtOAc 8:1, 10% NEt ); IR (KBr) ν 3119,
932, 2861, 2851, 1797, 1759, 1734, 1689, 1667, 1550,
hydroxypiperidine (7c) (42.0 mg, 413 µmol) and K CO3
(122 mg, 855 µmol) in MeCN (2.5 mL). Flash-SC (EtOAc/
3
max
2
507, 1473, 1443, 1410, 1370, 1350, 1305, 1278, 1260,
n-heptane 7:2, 10% NEt ). The product was solved in
3
−
1 1
248, 1224, 1202, 1164, 1106, 1069, 1011 cm ; H NMR
EtOAc and extracted three time with buffer (pH = 2). The
combined aqueous phases were cooled to 0 °C, and the pH
was adjusted to pH = 9 by adding buffer (pH = 10). The
(
500 MHz, CD Cl , TMS): δ = 1.41 (s, 2H), 1.47–1.57 (m,
2 2
8
2
H), 1.64 (s, 2H), 2.26 (t, J = 6.9 Hz, 2H), 2.32 (s, 4H),
.43 (s, 6H), 2.46 (s, 6H), 2.93–2.97 (m, 2H), 6.09 (s, 2H)
aqueous phase was extracted three times with CHCl . The
3
1
3
ppm; C NMR (125 MHz, CD Cl , TMS): δ = 14.6 (2C,
NCCH ), 16.6 (2C, NCCCH ), 25.0 (CH NCH CH CH ),
solvent was removed, and the remaining residue was solved
with MeCN, and the product was precipitated by adding
2
2
3
3
2
2
2
2
2
6.5 (2C, CH NCH CH CH ), 27.0 (CCH CH CH ), 28.6
H O. The MeCN was removed, and the remaining rest was
2
2
2
2
2
2
2
2
(
CCH CH ), 29.0 (CCH ), 32.1 (CH CH NCH CH CH ),
freeze-dried.
2
2
2
2
2
2
2
2
5
1
5.0 (2C, CH NCH CH CH ), 59.3 (CH NCH CH CH ),
72 mg (58%); orange solid; mp 73 °C; DC: R = 0.22
2
2
2
2
2
2
2
2
f
21.9 (2C, CCHC), 131.8 (2C, NCCCH ), 141.2 (2C,
(EtOAc/n-heptane 7:2, 10% NEt ); IR (KBr) ν
3407,
2
3
max
1
9
NCCCH), 147.4 (NCCCH ), 154.0 (2C, NCCH) ppm;
NMR (4710 MHz, CD Cl ): δ = −146.2 to −146.7 (m)
ppm; B NMR (160 MHz, CD Cl ): δ = −2.23 (t, J =
F
2933, 2862, 2802, 2770, 1550, 1510, 1474, 1409, 1371,
2
−
1
1
1309, 1225, 1201, 1159, 1079, 1027 cm ; H NMR
(400 MHz, DMSO-D6, 100 °C, TMS): δ = 1.13 (q, J =
10.4 Hz, 1H), 1.42 (dd, J = 24.3/11.0 Hz, 1H), 1.52 (s, 4H),
1.58–1.70 (m, 3H), 1.74–1.81 (m, 1H), 1.85 (t, J = 9.3 Hz,
1H), 1.96 (t, J = 10.7 Hz, 1H), 2.35 (s, 2H), 2.43 (s, 6H),
2
2
1
1
2
2
+
3
3.0 Hz) ppm; M (C H BF N ) = 401.28. MS (CI, CH )
23
34
2
+
3
5
m/z (%): 402.25 (44, [M+H] ), 382.25 (100); HRMS (EI+):
M calc. for C H BF N , 401.2808; found: 401.2815.
+
2
3
34
2
3
2.45 (s, 6H), 2.56–2.71 (m, 1H), 2.81 (dd, J = 10.5/3.3 Hz,
5
4
,5-Difluor-1,3,7,9-tetramethyl-10-(5-morpholinpentyl)-5H-
λ ,5 λ -dipyrrolo[1,2-c:2',1'-f][1,3,2]diazaborinin-4-ium-5-
1H), 2.89–3.19 (m, 2H), 3.51 (s, 1H), 4.19 (2, 1H), 6.21 (s,
2H) ppm; C NMR (100 MHz, DMSO-D6, 100 °C, TMS):
4
4
13
uide (10b) According to GP-3 (Method C): Compound 17
117 mg, 295 µmol) and morpholine (7b) (36.0 mg,
13 µmol) and K CO3 (122 mg, 855 µmol) in MeCN
δ = 13.9 (2C, NCCH ), 15.7 (2C, NCCCH ), 22.8
3
3
(
4
(NCH CH CH CH), 25.9 (CCH CH CH ), 27.4 (CCH
2 2 2 2 2 2 2
CH CH ), 27.94(CCH ), 31.3 (CH CH NCH CH), 33.1
2 2 2 2 2 2
2
(
2.5 mL). Flash-SC (1. n-heptan/EtOAc 5:4, 10% NEt , 2.
(NCH CHCH ), 53.0 (NCH CH CH CH), 57.5 (CH NCH
2 2 2 2 2 2 2
3
Gradient: n-heptane/EtOAc 5:4 → n-heptane/EtOAc 5:4,
CH), 61.0 (NCH CH), 65.9 (CHOH), 121.6 (2C, CCHC),
2
1
0% NEt3).
131.0 (2C, NCCCH ), 140.7 (2C, NCCCH ), 147.0
2
3
9
1
9
7.5 mg (82%); orange solid; mp 95–101 °C; DC: R =
(NCCCH2), 153.1 (2C, NCCH3) ppm;
F
NMR
f
0
3
1
.25 (n-heptane/EtOAc 5:4, 10% NEt ); IR (KBr) ν
(470 MHz, DMSO-D6): δ = −144.3 to −143.2 (m) ppm;
3
max
1
1
431, 2938, 2853, 2807, 1637, 1549, 1508, 1474, 1410,
B NMR (160 MHz, DMSO-D6): δ = −2.39 (t, J =
33.1 Hz) ppm; M (C H BF N O) = 417.28. MS (CI,
370, 1307, 1279, 1202, 1163, 1159, 1070, 1033 cm−
;
1
2
3
34
2
3
1
+
+
H NMR (500 MHz, CD Cl , TMS): δ = 1.49–1.58 (m,
CH ) m/z (%): 418.25 (34, [M+H] ), 1398.40 (100);
HRMS (EI+): M calc. for C H BF N O, 417.2758;
2
2
5
+
4
4
H), 1.60–1.69 (m, 2H), 2.31 (t, J = 6.8 Hz, 2H), 2.37 (s,
H), 2.43 (s, 6H), 2.46 (s, 6H), 2.92–3.00 (m, 2H), 3.64
2
3
34
2
3
found: 417.2769.
1
3
(
(
t, J = 4.7 Hz, 4H), 6.09 (s, 2H) ppm;
125 MHz, CD Cl ): δ = 14.2 (2C, NCCH ), 16.2 (2C,
C NMR
5,5-Difluoro-10-[5-(4-hydroxypiperidin-1-yl)pentyl]-1,3,7,9-
2
2
3
4
4
NCCCH ), 26.2 (CCH CH CH CH CH N), 28.0 (CCH
2
CH CH CH CH N), 28.6 (CCH ), 31.7 (CCH CH ), 53.8
tetramethyl-5H-4 λ ,5 λ -dipyrrolo[1,2-c:2',1'-f][1,3,2]diaza-
borinin-4-ium-5-uide (10d) According to GP-3 (Method
C): Compound 17 (117 mg, 295 µmol) and 4-
3
2
2
2
2
2
2
2
2
2
2
2
2
(
2C, NCH CH O), 58.5 (CH NCH CH O), 67.0 (2C,
2 2 2 2 2
NCH CH O), 121.6 (2C, CCHC), 131.4 (2C, NCCCH ),
hydroxypiperidine (7d) (42.0 mg, 413 µmol) and K CO3
2
2
2
2
1
40.8 (2C, NCCCH ), 146.9 (NCCCH ), 153.7 (2C,
(122 mg, 855 µmol) in MeCN (2.5 mL). Flash-SC (1.
3
2

Medicinal Chemistry Research
(58, [M+H] ), 458.30 (100), 174.15 (44); HRMS (EI+): M+
+
EtOAc/Isopropanol 8:1, 10% NEt , 2. Gradient: EtOAc/
3
Isopropanol 8:1 → EtOAc/Isopropanol 8:1, 10% NEt3).
calc. for C H BF N , 477.3121; found: 477.3129.
29
38
2
3
9
8 mg (80%); orange solid; mp 83 °C; DC: R = 0.33
f
(
3
1
EtOAc/Isopropanol 8:1, 10% NEt ); IR (KBr) νmax 3627,
5,5-Difluor-1,3,7,9-tetramethyl-10-{5-[4-phenyl-5,6-dihydro-
3
4
4
391, 2861, 2810, 1550, 1508, 1474, 1410, 1367, 1307,
pyridin-1(2H)-yl]pentyl}-5H-4 λ ,5 λ -dipyrrolo[1,2-c:2',1'-f]
[1,3,2]diazaborinin-4-ium-5-uid (10f) According to GP-3
(Method C): Compound 17 (560 mg, 1.41 mmol) and 4-
Phenyl-1,2,3,6-tetrahydropyridine (7f) (314 mg, 1.97 mmol)
and K CO (585 mg, 4.23 mmol) in MeCN (12.0 mL).
−
1
1
225, 1202, 1162, 1079, 987 cm ; H NMR (400 MHz,
DMSO-D6, TMS): δ = 1.27–1.40 (m, 2H), 1.47 (s, 4H),
1
2
2
1
.56 (s, 2H), 1.64–1.72 (m, 2H), 1.91 (t, J = 10.6 Hz, 2H),
.19–2.26 (m, 2H), 2.40 (s, 6H), 2.42 (s, 6H), 2.60–2.70 (m,
H), 2.87–2.98 (m, 2H), 3.36 (s, 1H), 4.55 (d, J = 4.2 Hz,
H), 6.24 (s, 2H) ppm; 13C NMR (125 MHz, DMSO-D6,
2
3
Flash-SC (1. n-heptane/EtOAc 8:2, 1% NEtMe , 2. Gra-
2
dient: n-heptane/EtOAc 8:2 → n-heptane/EtOAc 8:2, 2%
TMS): δ = 14.0 (2C, NCCH ), 15.7 (2C, NCCCH ), 26.0
NEtMe2).
3
3
(
(
(
(
CCH CH CH ), 27.4 (CCH CH CH CH CH N), 27.8
483 mg (72%); orange solid; mp 46–48 °C; DC: R = 0.25
2
2
2
2
2
2
2
2
f
CCH ), 31.0 (CCH CH ), 34.4 (2C, NCH CH CH), 51.0
(EtOAc/n-heptane 8:2, 2% NEtMe ); IR (KBr) ν = 2926,
2
2
2
2
2
2
max
2C, NCH CH CH), 57.2 (CH NCH CH CH), 66.4
28,63, 1549, 1510, 1473, 1309, 1200, 985, 747, 714,
2
2
2
2
2
−1 1
CHOH), 121.5 (2C, CCHC), 130.6 (2C, NCCCH2),
40.7 (2C, NCCCH ), 146.8 (NCCCH ), 152.9 (2C,
693 cm ; H NMR (400 MHz, CD Cl ): δ = 1.42–1.67 (m,
2 2
1
6H), 2.36 (s, 6H), 2.38 (s, 6H), 2.34–2.40 (m, 2H), 2.41–2.48
(m, 2H), 2.57 (t, J = 5.6 Hz, 2H), 2.85–2.94 (m, 2H), 3.02 (q,
J = 3.0 Hz, 2H), 5.96–6.04 (m, 3H), 7.09–7.19 (m, 1H),
3
2
1
9
NCCH ) ppm; F NMR (470 MHz, DMSO-D6): δ =
3
−
144.3 to −143.4 (m) ppm; 11B NMR (160 MHz, DMSO-
D6): δ = −2.41 (t, J = 32.9 Hz) ppm; M (C H BF N O)
1
3
7.18–7.27 (m, 2H), 7.27–7.35 (m, 2H) ppm; C NMR
2
3
34
2
3
+
=
1
417.28. MS (EI, 70 eV) m/z (%): 417.25 (14, M ),
(101 MHz, CD Cl ): δ = 14.2 (t, J = 2.5 Hz, 2C, H CCN),
2
2
3
+
14.15 (100); HRMS (EI+): M calc. for C H BF N O,
16.2 (2C, H CCCN), 26.9 (CCH CH CH CH CH N), 28.1
3 2 2 2 2 2
2
3
34
2
3
4
17.2758; found: 417.2762.
(2C, CCH CH CH CH CH N, NCH CH C), 28.5 (CCH
2 2 2 2 2 2 2 2
CH CH CH CH N), 31.8 (CCH CH CH CH CH N), 50.4
2
2
2
2
2
2
2
2
2
5
,5-Difluoro-1,3,7,9-tetramethyl-10-[5-(4-phenylpiperidin-1-
(NCH CH C), 53.3 (NCH CH), 57.9 (CCH CH CH
2 2 2 2 2 2
CH CH N), 121.5 (2C, CCHC), 122.1 (NCH CH), 124.7
2 2 2
4
4
yl)pentyl]-5H-4 λ ,5 λ -dipyrrolo[1,2-c:2',1'-f][1,3,2]diazabor-
inin-4-ium-5-uide (10e) According to GP-3 (Method C):
Compound 17 (117 mg, 295 µmol) and 4-phenylpiperidine
(2C, CC C H), 126.8 (C C HC HC H), 128.2 (2C,
ar ar
ar ar
ar
ar
CC HC HC H), 131.3 (2C, NCCCH ), 134.8 (CC ),
ar
ar
ar
2
ar
(
7e) (67.0 mg, 413 µmol) and K CO (122 mg, 855 µmol) in
140.8 (2C, H CCCN), 140.9 (CC ), 146.9 (NCCCH ),
3 ar 2
2
3
19
MeCN (2.5 mL). Flash-SC (1. n-heptane/EtOAc 7:2, 10%
NEt , 2. Gradient: n-heptane/EtOAc 7:2 → n-heptane/
EtOAc 7:2, 10% NEt3).
153.6 (2C, H CCN) ppm; F NMR (470 MHz, CD Cl ):
3 2 2
11
δ = −146.7 to −146.5 (m) ppm; B NMR (160 MHz,
CD Cl ): δ = 0.52 (t, J = 33.1 Hz) ppm; HRMS (ESI): [M
3
2
2
+
1
22 mg (87%); orange solid; mp 109–111 °C; DC: R =
+H] calc. for C H BF N ,476.3043; found: 476.3047.
f
29 37 2 3
0
3
1
1
1
1
2
2
7
.33 (EtOAc/n-heptane 7:2, 10% NEt ); IR (KBr) ν
424, 3028, 2925, 2861, 2801, 1768, 1550, 1510, 1470,
3
max
4
4
1-[5-(5,5-Difluoro-1,3,7,9-tetramethyl-5H-4λ ,5λ -dipyrrolo
[1,2-c:2',1'-f][1,3,2]diaza-borinin-10-yl)pentyl]-4-phenylpi-
peridin-4-ol (10g) According to GP-3 (Method C):
Compound 17 (117 mg, 295 µmol) and 4-hydroxy-4-
409, 1364, 1307, 1261, 1225, 1200, 1156, 1109, 1074,
−
1
1
025 cm ;
H NMR (500 MHz, DMSO-D6): δ =
.46–1.55 (m, 4H), 1.55–1.65 (m, 4H), 1.71 (d, J =
0.9 Hz, 2H), 1.93 (t, J = 10.8 Hz, 2H), 2.30 (t, J = 6.5 Hz,
H), 2.40 (s, 6H), 2.43 (s, 7H), 2.90–2.98 (m, 4H), 6.24 (s,
H), 7.15–7.20 (m, 1H), 7.22 (dd, J = 3.3/5.0 Hz, 2H),
.25–7.31 (m, 2H) ppm; 13C NMR (125 MHz, DMSO-D6,
phenylpiperidin (7g) (73.0 mg, 413 µmol) and K CO3
(122 mg, 855 µmol) in MeCN (2.5 mL). Flash-SC (1. n-
heptane/EtOAc 5:4, 10% NEt , 2. Gradient: n-heptane/
EtOAc 5:4 → n-heptane/EtOAc 5:4, 10% NEt3).
2
3
TMS): δ = 14.0 (2C, NCCH ), 15.8 (2C, NCCCH ), 25.8
126 mg (87%); orange solid; mp 162–164 °C; DC: R =
3
3
f
(
CCH CH CH ), 27.5 (CCH CH ), 27.8 (CCH ), 31.1
0.15 (EtOAc/n-heptane 5:4, 10% NEt ); IR (KBr) ν
2
2
2
2
2
2
3
max
(
CH CH NCH CH C), 33.1 (2C, NCH CH C), 41.9 (CC ),
3425, 2924, 2828, 2780, 1554, 1535, 1513, 1471, 1447,
2
2
2
2
2
2
ar
5
3.7 (2C, NCH CH C), 57.7 (CH NCH CH C), 121.6 (2C,
2 2 2 2 2
1411, 1311, 1257, 1207, 1158, 1139, 1117, 1103, 1080,
1061, 1022 cm ; H NMR (500 MHz, CD Cl , TMS): δ =
2 2
−1 1
CCHC), 125.9 (CC C HC HC H , 126.6 (2C, CC C H-
ar ar
ar
ar
)
ar ar
C HC H), 128.2 (2C, CC C HC HC H), 130.6 (2C,
1.57 (s, 4H), 1.63–1.73 (m, 4H), 2.09 (td, J = 4.4/13.2 Hz,
2H), 2.32–2.42 (m, 4H), 2.44 (s, 6H), 2.47 (s, 6H) 2.76 (d,
J = 11.4 Hz, 2H), 2.95–3.00 (m, 2H), 6.09 (s, 2H), 7.25 (t,
J = 7.3 Hz, 1H), 7.35 (t, J = 7.7 Hz, 2H), 7.50 (dd, J = 1.0/
ar
ar
ar ar
ar
ar
NCCCH ), 140.7 (2C, NCCCH ), 146.2 (CC ), 146.8
2
3
ar
19
(
NCCCH ), 152.9 (2C, NCCH ) ppm; F NMR (470 MHz,
2 3
DMSO-D6): δ = −143.8 to −144.3 (m) ppm; B NMR
11
1
3
(
160 MHz, DMSO-D6): δ = −2.39 (t, J = 32.9 Hz) ppm; M
8.2 Hz, 2H) ppm; C NMR (100 MHz, CD Cl , TMS): δ =
2 2
+
(
C H BF N ) = 477.31 MS (CI, CH ) m/z (%): 478.30
14.6 (2C, NCCH ), 16.6 (2C, NCCCH ), 27.2 (CCH CH ),
3 3 2 2
2
9
38
2
3
5

Medicinal Chemistry Research
2
8.6 (CCH CH CH ), 29.0 (CCH2), 32.2 (CH CH
2
MeCN (2.5 mL). Flash-SC (n-heptane/EtOAc 5:4, 10%
2
2
2
2
NCH CH C), 39.1 (2C, NCH CH C), 50.0 (2C,
NEt3).
2
2
2
2
NCH CH C), 58.7 (CH NCH CH C), 71.6 (COH), 121.9
86 mg (56%); orange solid; mp 99–108 °C; DC: R = 0.28
2
2
2
2
2
f
(
2C, CCHC), 125.0 (2C, C C HC HC H), 127.2 (C
(EtOAc/n-heptane 5:4, 10% NEt ); IR (KBr) ν
3375,
ar ar
ar
ar
ar-
3
max
C HC HC H), 128.6 (2C, C C HC HC H), 131.8 (2C,
2926, 2852, 1609, 1549, 1510, 1471, 1410, 1373, 1308,
ar
ar
ar
ar ar
ar
ar
−
1 1
NCCCH ), 141.2 (2C, NCCCH ), 147.4 (NCCCH ), 149.26
1249, 1224, 1200, 1159, 1109, 1079, 1030 cm ; H NMR
(500 MHz, MeOD-D3, TMS): δ = 1.50–1.59 (m, 2H),
1.60–1.70 (m, 4H), 1.74 (d, J = 12.4 Hz, 2H), 2.07 (td, J
= 4.3/13.4 Hz, 2H) 2.42 (s, 6H), 2.42–2.44 (m, 8H), 2.53 (t,
J = 11.1 Hz, 2H), 2.80 (d, J = 11.3 Hz, 2H), 2.94–3.01 (m,
2H), 3.76 (s, 3H), 6.12 (s, 2H), 6.85–6.90 (m, 2H),
2
3
2
19
(
CC ), 154.0 (2C, NCCH ) ppm; F NMR (470 MHz,
ar 3
CD Cl ): δ = −146.1 to −146.9 (m) ppm; B NMR
1
1
2
2
(
(
(
160 MHz, CD Cl ): δ = −2.31 (t, J = 33.0 Hz) ppm; M
2 2
+
C H BF N O) = 493.31 MS (CI, CH ) m/z (%): 494.30
2
9
38
2
3
5
+
39, [M+H] ), 476.30 (47), 259.15 (100); HRMS (EI+):
+
13
M calc. for C H BF N O, 493.3071; found: 493.3070.
7.36–7.42 (m, 2H) ppm; C NMR (125 MHz, MeOD-D3):
2
9
38
2
3
δ = 14.4 (2C, NCCH ), 16.6 (2C, NCCCH ), 27.4
3
3
5
1
,5-Difluoro-10-{5-[4-hydroxy-4-(2-methoxyphenyl)piperidin-
-yl]pentyl}-1,3,7,9-tetramethyl-5H-4 λ ,5 λ -dipyrrolo[1,2-
(CCH CH CH CH ), 29.3 (CCCH CH ), 29.3 (CCCH ),
32.9 (CCH CH CH ), 38.8 (2C, NCH CH C), 50.7 (2C,
2 2 2 2 2
2 2 2 2 2 2 2
4
4
c:2',1'-f][1,3,2]diazaborinin-4-ium-5-uide (10h) According
to GP-3 (Method C): Compound 17 (117 mg, 295 µmol)
and 4-(2-methoxyphenyl)piperidin-4-ol (7h) (86.0 mg,
NCH CH C), 55.6 (OCH ), 59.8 (CH NCH CH C), 71.2
2 2 3 2 2 2
(COH), 114.4 (2C, C C HC HC O), 122.6 (2C, CCHC),
ar ar
ar
ar
126.9 (2C, C C HC HC O), 132.6 (2C, NCCCH ), 142.0
ar ar
ar
ar
2
4
13 µmol) and K CO3 (122 mg, 855 µmol) in MeCN
(CC ), 142.2 (2C, NCCCH ), 148.1 (NCCCH ), 154.9 (2C,
ar 3 2
2
1
9
(
2.5 mL). Flash-SC (n-heptane/EtOAc 5:4, 10% NEt3).
12 mg (73%); orange solid; mp 78 °C; DC: R = 0.42
NCCH ), 160.0 (C O) ppm; F NMR (470 MHz, MeOD-
3 ar
1
1
1
D3): δ = −147.6 to −146.6 (m) ppm; B NMR (160 MHz,
MeOD-D3): δ = −2.27 (t, J = 32.6 Hz, H) ppm; M
f
(
EtOAc/n-heptane 5:4, 10% NEt ); IR (KBr) νmax 3433,
3
+
2
1
1
1
928, 2864, 2812, 2771, 1550, 1511, 1490, 1471, 1437,
(C H BF N O ) = 523.32 MS (CI, CH ) m/z (%):
3
0
40
2
3
2
5
+
409, 1372, 1309, 1229, 1201, 1159, 1109, 1080, 1041,
524.20 (63, [M+H] ), 606.30 (63), 486.20 (100); HRMS
−
1 1
(EI+): M+ calc. for C H BF N O , 523.3176; found:
025 cm ; H NMR (500 MHz, MeOD-D3, TMS): δ =
.55 (q, J = 8.14 Hz, 2H) 1.62–1.74 (m, 6H), 2.39–2.46
3
0
40
2
3
2
523.3183.
(
m, 12H), 2.46–2.57 (m, 4H), 2.61 (t, J = 11.8 Hz, 2H),
2
3
8
1
.83 (d, J = 11.2 Hz, 2H), 2.94–3.03 (m, 2H), 3.85 (s,
H), 6.12 (s, 2H), 6.93 (t, J = 7.6 Hz, 1H), 6.98 (d, J =
.2 Hz, 1H), 7.21–7.25 (m, 1H), 7.48 (dd, J = 1.7/7.8 Hz,
4-(2-Chlorophenyl)-1-[5-(5,5-difluoro-1,3,7,9-tetramethyl-
4
4
5H-4λ ,5λ -dipyrrolo[1,2-c:2′,1′-f][1,3,2]diazaborinin-10-yl)
pentyl]piperidin-4-ol (10j) According to GP-3 (Method C):
Compound 17 (117 mg, 295 µmol) and 4-(2-chlorophenyl)
1
3
H) ppm; C NMR (125 MHz, MeOD-D3): δ = 14.4
(
(
(
(
(
(
2C,
NCCH3),
16.6
(2C,
29.2
NCCCH3),
27.2
29.3
piperidin-4-ol (7j) (87.0 mg, 413 µmol) and K CO3
(122 mg, 855 µmol) in MeCN (2.5 mL). Flash-SC (1. n-
2
CH CH NCH CH C),
(CCCH CH ),
2
2
2
2
2
2
CCCH CH ), 32.9 (CH CH CH NCH CH C), 35.5
2C, NCH CH C), 50.4 (2C, NCH CH C), 55.6
OCH ), 59.7 (CH NCH CH C), 71.9 (COH), 112.7
heptane/EtOAc 1:1, 10% NEt , 2. Gradient: n-heptane/
2
2
2
2
2
2
2
3
EtOAc 1:1 → n-Heptane/EtOAc 1:1, 10% NEt3).
2
2
2
2
130 mg (83%); orange solid; mp 160 °C dec. DC: R =
3
2
2
2
f
CC C C H), 121.7 (CC C HC H), 122.6 (2C,
0.2 (n-heptane/EtOAc 1:1, 10% NEt ); IR (KBr) ν 3427,
ar ar ar
ar ar
ar
3
max
CCHC), 127.0 (CC C H), 129.5 (C C C HC H),
2925, 2864, 2811, 1625, 1550, 1510, 1471, 1432, 1409,
ar ar
ar ar ar
ar
1
32.6 (2C, NCCCH2), 136.5 (CCar), 142.2 (2C,
1371, 1309, 1263, 1225, 1201, 1158, 1107, 1079, 1063,
−
1
1
NCCCH ), 148.1 (NCCCH ), 154.9 (2C, NCCH ),
1
δ = −147.5 to −146.9 (m) ppm; B NMR (160 MHz,
MeOD-D3): δ = −2.25 (t, J = 32.5 Hz) ppm;
1037 cm ; H NMR (500 MHz, CD Cl , TMS): δ =
3
2
3
2
2
1
9
58.3 (C O) ppm; F NMR (470 MHz, MeOD-D3):
1.51–1.62 (m, 4H), 1.64–172 (m, 2H), 1.95 (dd, J = 2.4/
13.4 Hz, 2H), 2.27–2.43 (m, 6H), 2.44 (s, 6H), 2.46 (s, 6H),
2.76 (d, J = 10.9 Hz, 2H), 2.93–3.01 (m, 2H), 6.09 (s, 2H),
7.22 (td, J = 1.7/7.6 Hz, 1H), 7.28 (td, J = 1.5/7.6 Hz, 1H),
7.37 (dd, J = 1.4/7.8 Hz, 1H), 7.60 (dd, J = 1.7/7.9 Hz, 1H)
ar
1
1
M
+
(
C H BF N O ) = 523.32 MS (FAB , NBA) m/z (%):
30 40 2 3 2
+
+
+
5
24.3 ([M+H] ); HRMS (FAB , NBA): [M+H] calc.
1
3
for C H BF N O , 524.3254; found: 524.3264.
ppm; C NMR (125 MHz, CD Cl , TMS): δ = 14.6 (2C,
3
0
41
2
3
2
2 2
NCCCH ), 16.6 (2C, NCCCH ), 27.2 (CCH CH CH ),
3
3
2
2
2
5
,5-Difluoro-10-{5-[4-hydroxy-4-(4-methoxyphenyl)piperi-
28.6
(CCH CH CH ),
29.0
(NCCCH2),
32.2
2
2
2
4
4
din-1-yl]pentyl}-1,3,7,9-tetramethyl-5H-4 λ ,5 λ -dipyrrolo
1,2-c:2',1'-f][1,3,2]diazaborinin-4-ium-5-uide (10i) Accord-
ing to GP-3 (Method C): Compound 17 (117 mg,
95 µmol) and 4-(4-methoxyphenyl)piperidin-4-ol (7i)
86.0 mg, 413 µmol) and K CO3 (122 mg, 855 µmol) in
(CCH CH CH CH ), 36.1 (2C, NCH CH C), 49.7 (2C,
2 2 2 2 2 2
NCH CH C), 58.6 (CH NCH CH C), 72.4 (COH), 121.9
2 2 2 2 2
(2C, CCHC), 127.5 (CC C H), 127.7 (CC C HC H),
128.8 (C C C HC H), 131.8 (2C, NCCCH ), 132.0
ar ar ar ar 2
[
ar ar
ar ar
ar
2
(
(C C C H), 132.3 (C Cl), 141.2 (2C, NCCCH ), 144.4
ar ar ar ar 3
2

Medicinal Chemistry Research
CC ), 147.4 (NCCCH ), 154.0 (2C, NCCH ) ppm; 19F
1159, 1079, 1029 cm−1; H NMR (500 MHz, CD Cl ,
1
(
ar
2
3
2 2
NMR (470 MHz, CD Cl ): δ = −146.1 to −146.9 (m) ppm;
TMS): δ = 1.23 (t, J = 7.14 Hz, 3H), 1.37–1.60 (m, 6H),
1.60–1.73 (m, 3H), 1.84–1.92 (m, 1H), 1.95 (t, J = 10.1 Hz,
1H), 2.11 (t, J = 10.7 Hz, 1H), 2.32 (t, J = 6.9 Hz, 2H), 2.43
(s, 6H), 2.46 (s, 7H), 2.68 (d, J = 10.7 Hz, 1H), 2.89 (d, J =
9.9 Hz, 1H), 2.92–2.99 (m, 2H), 4.08 (q, J = 7.1 Hz, 2H),
2
2
1
1
B NMR (160 MHz, CD Cl ): δ = −0.47 (t, J = 33.0 Hz)
2
2
ppm; M (C H BClF N O) = 527.27 MS (EI, 70 eV) m/z
2
9
37
2
3
+
(
%): 527.36 (20, M ), 224.05 (69), 199 (90), 94.05 (100);
HRMS (EI+): M calc. for C H BClF N O, 527.2681;
+
29
37
2
3
1
3
found: 527.2681.
6.09 (s, 2H) ppm; C NMR (125 MHz, CD Cl , TMS): δ
2 2
=
14.4 (2C, NCCCH ), 14.6 (OCH CH ), 16.6 (2C,
3 2 3
1
5
0-{5-[4-(4-Chlorophenyl)-4-hydroxypiperidin-1-yl]pentyl}-
,5-difluoro-1,3,7,9-tetramethyl-5H-4 λ ,5 λ -dipyrrolo[1,2-
NCCCH3), 25.1 (NCH CH CH CH), 27.0 (CH CH2
2 2 2 2
NCH CH), 27.5 (NCH CH CH CH), 28.4 (CCH CH CH ),
2 2 2 2 2 2 2
4
4
c:2′,1′-f][1,3,2]diazaborinin-4-ium-5-uide (10k) According
to GP-3 (Method C): Compound 17 (117 mg, 295 µmol)
and 4-(4-chlorophenyl)piperidin-4-ol (7k) (87.0 mg,
29.0 (CCH ), 32.1 (CCH CH ), 42.4 (NCH CH), 53.8
2 2 2 2
(NCH CH CH CH), 56.0 (NCH CH), 58.7 (CH NCH CH),
2
2
2
2
2
2
60.5 (OCH ), 121.9 (2C, CCHC), 131.8 (2C, NCCCH ),
2
2
4
13 µmol) and K CO3 (122 mg, 855 µmol) in MeCN
141.2 (2C, NCCCH ), 147.4 (NCCCH ), 154.0 (2C,
3 2
2
1
9
(
2.5 mL). Flash-SC (1. n-heptane/EtOAc 5:4, 10% NEt , 2.
NCCH ), 174.5 (CO) ppm; F NMR (375 MHz, CD Cl ):
3 2 2
3
1
1
Gradient: n-heptane/EtOAc 5:4 → n-heptane/EtOAc 5:4,
0% NEt3).
21 mg (77%); orange solid; mp 119 °C; DC: R = 0.24
δ = −146.3 to −146.8 (m) ppm; B NMR (160 MHz,
CD Cl ): δ = −0.47 (t, J = 32.9 Hz) ppm;
1
M
2
2
+
1
(C H BF N O ) = 473.30 MS (FAB , NBA) m/z (%):
473.5 (M ); HRMS (FAB , NBA): M calc. for
f
26 38
2
+
3
2
+
+
(
2
1
n-heptane/EtOAc 5:4, 10% NEt ); IR (KBr): ev = 3426,
3
929, 2863, 2813, 2361, 2342, 1550, 1510, 1474, 1409,
C H BF N O , 473.3020; found: 473.3028.
2
6
38
2
3
2
−
1
1
373, 1309, 1225, 12101, 1159, 1080 cm . H NMR
(
500 MHz, CD Cl , TMS): δ = 1.50–1.62 (m, 4H),
10-[5-(3-Carboxypiperidin-1-yl)pentyl]-5,5-difluoro-1,3,7,9-
2
2
4
4
1
4
2
7
.63–1.71 (m, 4H), 2.01–2.10 (m, 2H), 2.30–2.43 (m,
H), 2.44 (s, 6H), 2.47 (s, 6H), 2.76 (d, J = 10.6 Hz, 2H),
.94–2.99 (m, 2H), 6.09 (s, 2H), 7.30–7.34 (m, 2H),
.43–7.47 (m, 2H) ppm; 13C NMR (100 MHz, CD Cl ,
tetramethyl-5H-4 λ ,5 λ -dipyrrolo[1,2-c:2',1'-f][1,3,2]diaza-
borinin-4-ium-5-uide (10m) According to GP-2: Com-
pound 10l (389 mg, 0.82 mmol) in 11.0 mL solvent mixture
(CH Cl /MeOH, 2:1) and LiOH (49.0 mg, 2.10 mmol)
2
2
2
2
TMS): δ = 14.6 (2C, NCCH ), 16.6 (2C, NCCCH ), 27.1
solved in H O (2.1 mL). The reaction mixture was stirred
3
3
2
(
CCCH CH ), 28.6 (CCCH CH CH ), 28.9 (CCCH ), 32.1
for 7 d. The pH was adjusted to pH = 7 by adding HCl
(0.1 M).
2
2
2
2
2
2
(
CH CH CH N), 38.9 (2C, NCH CH C), 49.8 (2C,
2
2
2
2
2
NCH CH C), 58.6 (CH NCH CH C), 71.4 (COH), 121.9
281 mg (77%); orange solid; Mp 105–107 °C dec; IR
(KBr) νmax 3433, 2933, 2866, 1702, 1629, 1549, 1511,
1474, 1408, 1371, 1308, 1224, 1200, 1159, 1080,
2
2
2
2
2
(
2C, CCHC), 126.7 (2C, C C HC HC Cl), 128.6 (2C,
ar ar ar ar
C C HC HC Cl), 131.8 (2C, NCCCH ), 132.8 (C Cl)
ar ar
ar
ar
2
ar
1028 cm− . H NMR (400 MHz, C D Cl , 40 °C, TMS):
1
1
1
1
41.2 (2C, NCCCH ), 147.3 (NCCCH ), 147.9 (CC ),
3
2
ar
2 2 4
19
54.0 (2C, NCCCH ) ppm; F NMR (470 MHz, CD Cl ):
δ = 1.45–1.76 (m, 8H), 1.79–1.95 (m, 1H), 2.01 (d, J =
13.8 Hz, 1H), 2.28 (t, J = 11.9 Hz, 1H), 2.41 (s, 7H), 2.49
(s, 6H), 2.56 (dt, J = 3.9/7.5 Hz, 2H), 2.68 (s, 1H), 2.95
(dd, J = 7.0/9.8 Hz, 2H), 3.03 (d, J = 11.7 Hz, 1H), 3.13
3
2
2
11
δ = −146.2 to −146.9 (m) ppm; B NMR (160 MHz,
CD Cl ): δ = −2.30 (t, J = 33.0 Hz) ppm;
M
2
2
(
(
C H BClF N O) = 527.27 MS (FAB, NBA) = 528.30
[M+H] ). HRMS (FAB, NBA): [M+H] calc. for
29 37 2 3
+
+
13
(d, J = 11.2 Hz, 1H), 6.08 (s, 2H) ppm; C NMR
C H BClF N O, 528.2759; found: 528.2766.
(100 MHz, C D Cl , 40 °C, TMS): δ = 14.5 (2C,
2
9
38
2
3
2
2
4
NCCH ), 16.3 (2C, CCCH ), 21.7 (NCH CH CH CH),
3
3
2
2
2
1
0-{5-[3-(Ethoxycarbonyl)piperidin-1-yl]pentyl}-5,5-
25.5
(CCH CH ),
26.2
(CH CH CHC),
27.6
2
2
2
2
4
4
difluoro-1,3,7,9-tetramethyl-5H-4 λ ,5 λ -dipyrrolo[1,2-c:
',1'-f][1,3,2]diazaborinin-4-ium-5-uide (10l) According to
(CCH CH CH ), 28.1 (CCH ), 31.4 (CCH CH CH CH ),
2 2 2 2 2 2 2 2
39.8 (CHCO), 53.0 (NCH CH CH CH), 55.0 (NCH CH),
2 2 2 2
2
GP-3 (Method C): Compound 17 (351 mg, 885 µmol) and
ethyl piperidine-3-carboxylate (7l) (201 mg, 1.24 mmol,
57.0 (CCH CH CH CH CH N), 121.8 (2C, CCHC),
2 2 2 2 2
131.3 (2C, CCCH ), 140.4 (2C, NCCCH ), 145.8
3
2
1
9
0
.2 mL) and K CO3 (367 mg, 2.65 mmol) in MeCN
(CCH ), 154.0 (2C, NCCH ), 176.2 (CO) ppm;
F
2
2
3
(
7.5 mL). Flash-SC (1. n-heptane/EtOAc 8:1, 10% NEt , 2.
NMR (470 MHz, C D Cl ): δ = −144.3 to −147.0 (m)
3
2 2 4
1
1
Gradient: n-heptane/EtOAc 8:1 → n-heptane/EtOAc 1:1,
1
ppm; B NMR (160 MHz, C D Cl ): δ = −0.45 (t, J =
2 2 4
+
0% NEt3).
32.9 Hz) ppm; M (C H BF N O ) = 445.27; MS (FAB ,
24 34 2 3 2
+
+
3
98 mg (95%); red oil. DC: R = 0.16 (n-heptane/EtOAc
NBA) m/z (%): 446.3 ([M+H] ); HRMS (FAB , NBA):
[M+H]+ calc. for C H BF N O , 446.2785; found:
f
8
1
:1, 10% NEt ); IR (film) ν
2939, 2864, 2805, 2770,
max
3
24 35
2
3
2
730, 1550, 1511, 1474, 1410, 1371, 1309, 1224, 1201,
446.2787.

Medicinal Chemistry Research
1
4
0-(3-Chloropropyl)-5,5-difluoro-1,3,7,9-tetramethyl-5H-
λ ,5 λ -dipyrrolo[1,2-c:2',1'-f][1,3,2]diazaborinin-4-ium-5-
−146.1 to −146.7 (m) ppm; 11B NMR (160 MHz, CD Cl ):
2 2
4
4
δ = −2.34 (t, J = 32.8 Hz) ppm; M (C H BF N O S) =
23 27 2 2 3
+
+
uide (15a) According to GP-1: 4-Chlorobutyrylchloride
460.18. MS (CI, CH ) m/z (%): 461.12 (12, [M+H] ),
5
+
(
(
12) (1.15 g, 8.15 mmol, 915.0 µL) and 2,4-Dimethylpyrrole
11) (1.57 g, 16.5 mmol, 1.7 mL) in CH Cl (90.0 mL), as
442.20 (31), 441.20 (100); HRMS (EI+): M calc. for
C H BF N O S, 460.1798; found: 460.1821.
2
2
23 27
2
2
3
well as NEt (3.89 g, 38.0 mmol, 5.4 mL) and BF •OEt
2
3
3
(
7.83 g, 55.2 mmol, 7.0 mL) in toluene (190.0 mL) and
10-(4-Chlorobutyl)-5,5-difluoro-1,3,7,9-tetramethyl-5H-
4
4
CH Cl (10.0 mL). Flash-SC (n-Pentane/EtOAc = 9:1)
4 λ ,5 λ -dipyrrolo[1,2-c:2',1'-f][1,3,2]diazaborinin-4-ium-5-
uide (16) According to GP-1: 5-Chloropentanoylchloride
(13) (1.86 g, 12.0 mmol, 1.6 mL) and 2,4-Dimethylpyrrole
(11) (2.35 g, 24.0 mmol, 2.6 mL) in CH Cl (135.0 mL), as
2
2
(
Kamkaew and Burgess 2013).
30 mg (35%); orange solid; mp 169 °C; DC: R = 0.55
9
f
(
n-pentane/EtOAc = 9:1); IR (KBr) νmax3416, 2962, 2923,
2
2
2
1
1
362, 1702, 1551, 1531, 1508, 1478, 1444, 1430, 1405,
well as NEt3 (5.83, 57.0 mmol 8.0 mL) and BF •OEt2
(11.8 g, 83.0 mmol, 10.5 mL) in toluene (285.0 mL) and
3
365, 1349, 1306, 1270, 1210, 1194, 1155, 1099, 1075,
−
1 1
048, 1022, 990 cm ; H NMR (500 MHz, CDCl , TMS):
CH Cl (15.0 mL). Flash-SC (i-Hexane/CH CL = 1:1)
3
2
2
2
2
δ = 2.05–2.12 (m, 2H), 2.44 (s, 6H), 2.52 (s, 6H),
.11–3.17 (m, 2H), 3.71 (t, J = 6.0, 2H), 6.06 (s, 2H)
(Esfandiari et al. 2010).
1.86 g (46%); orange solid; mp 168 °C; DC: R = 0.27 (i-
3
f
1
3
ppm C NMR (100 MHz, CDCl ): δ = 14.7 (2C, CHC
hexane/CH Cl = 1:1); IR (KBr) ν
3127, 2995, 2963
max
3
2
2
(
(
(
1
CH )CC), 16.7 (2C, NCCH3), 26.1 (CH C), 34.2
2927, 2874, 1549, 1534, 1508, 1476, 1446, 1409, 1366,
3
2
−
1
ClCH CH ), 44.9 (ClCH ), 122.0 (2C, CCHC), 131.6
1308, 1254, 1204, 1161, 1111, 1079, 1071, 1023, 988 cm ;
2
2
2
1
2C, NCCCH), 140.5 (2C, NCCCH), 144.6 (NCCCH ),
H NMR (500 MHz, CDCl , TMS): δ = 1.76–1.84 (m, 2H),
2
3
19
54.5 (2C, NCCH) ppm; F NMR (470 MHz, CDCl ): δ =
1.93–2,00 (m, 2H), 2.41 (s, 6H), 2.52 (s, 6H), 2.94–2.99 (m,
3
146.7 to −146.1 (m) ppm; 11B NMR (160 MHz, CDCl3):
2H), 3.58 (t, J = 6.4, 2H), 6.06 (s, 2H) ppm; C NMR
13
−
δ = −1.99 (t, J = 32.9) ppm; M (C H BClF N ) = 324.14
MS (CI) m/z (%): 325 (35, [M+H] ), 305 (100); HRMS
(125 MHz, CDCl ): δ = 14.7 (2C, NCCH ), 16.6 (2C,
16
20
2
2
3
3
+
NCCCH3), 27.8 (CCH2), 29.1 (CCH CH ), 33.1
2 2
(
EI): M calc. for C H BClF N , 324.1371; found:
(CH CH Cl), 44.5 (CH Cl) 121.9 (2C, CCHC), 131.6
2 2 2
16
20
2
2
3
24.1369.
(2C, NCCCH), 140.5 (2C, NCCCH), 145.6 (NCCCH ),
2
1
9
1
54.3 (2C, NCCH ) ppm; F NMR (500 MHz, CDCl ):
3
3
1
1
5,5-Difluoro-1,3,7,9-tetramethyl-10-[3-(tosyloxy)propyl]-5H-
4
δ = −146.4 to −146.7 ppm; B NMR (160 MHz, CDCl3):
δ = −1.91 (t J = 32.9 Hz) ppm; M (C H BClF N ) =
4
4
λ ,5 λ -dipyrrolo[1,2-c:2',1'-f][1,3,2]diazaborinin-4-ium-5-
1
7
22
2
+
2
+
uide (15b) 19 (1.38 g, 4.51 mmol) was solved in CH Cl
338.15. MS (CI, CH ) m/z (%): 339 (33, [M+H] ), 319
2
2
5
(
45.0 mL) and cooled to 0 °C. After adding of NEt (1.46 g,
(100); HRMS (EI+): M calc. for C H BClF N ,
3
17 22
2
2
1
4.4 mmol, 1.9 mL) and DMAP (55.0 mg, 0.450 mmol), p-
338.1533; found: 338.1537.
toluolsulfonylchloride (1.72 g, 9.02 mmol) was added and
the reaction mixture was allowed to warm up to room
temperature and was stirred overnight afterwards. After
10-(5-Bromopentyl)-5,5-difluoro-1,3,7,9-tetramethyl-5H-
4
4
4 λ ,5 λ -dipyrrolo[1,2-c:2',1'-f][1,3,2]diazaborinin-4-ium-5-
uide (17) According to GP-1: 5-Bromovalerylchloride
(14) (1.71 g, 8.00 mmol, 1.2 mL) and 2,4-Dimethylpyrrol
(11) (1.57 g, 16.0 mmol, 1.7 mL) in CH CL (90.0 mL), as
washing with H O and brine, the organic phase was dried
2
over Na SO , filtered, and the solvent was removed. The
2
4
remaining residue was purified by flash-SC (CH Cl /iso-
2
2
2
2
hexane 3:1).
.94 g (94%); orange solid; mp 171–173 °C; R = 0.3
well as NEt (3.89 g, 38.0 mmol, 5.4 mL) and BF •OEt
3 3 2
(7.83 g, 55.0 mmol, 7.0 mL) in toluene (190.0 mL) and
1
f
(
CH Cl /iso-Hexan 3:1); IR (KBr) ν
2960, 2924, 1598,
CH CL (10.0 mL). Flash-SC (n-heptane/EtOAc = 9:1).
2
2
max
2
2
1
1
552, 1512, 1473, 1408, 1361, 1307, 1277, 1224, 1203,
176, 1159, 1096, 1077, 1026 cm ; H NMR (400 MHz,
1.43 g (45%); orange solid; mp 134 °C; DC: R = (0.27);
IR (KBr) νmax 3442, 2956, 2929, 2867, 1552, 1532, 1509,
f
−
1 1
CD Cl , TMS): δ = 1.94 (dt, J = 5.8/17.2 Hz, 2H), 2.36 (s,
1475, 1439, 1408, 1371, 1340, 1307, 1270, 1251, 1224,
2
2
−
1 1
6
2
8
1
2
H), 2.45 (s, 9 H), 2.96–3.02 (m, 2H), 4.16 (t, J = 5.9 Hz,
1200, 1157, 1106, 1079, 1070, 1062, 1026 cm ; H NMR
(500 MHz, CDCl3, TMS): δ = 1.62–1.68 (m, 4H),
1.85–1.99 (m, 2H), 2.42 (s, 6H), 2.51 (s, 6H), 2.93–2.98
H), 6.08 (s, 2H), 7.39 (d, J = 7.9 Hz, 2H), 7.78 (d, J =
1
3
.3 Hz, 2H) ppm; C NMR (100 MHz, CD Cl , TMS): δ =
2
2
13
4.6 (2C, NCCH ), 16.6 (2C, NCCCH ), 21.8 (H CC ),
(m, 2H), 3.43 (t, J = 6.6 Hz, 2H), 6.06 (s, 2H) ppm;
C
3
3
3
ar
5.0 (CCH ), 31.2 (CH CH O), 70.1 (CH O), 122.2 (2C,
NMR (100 MHz, CDCl ): δ = 14.6 (2C, NCCH ), 16.6 (2C,
2
2
2
2
3
3
CCHC), 128.2 (2C, SC C HC HC ), 130.4 (2C, SC
NCCCH3), 28.4 (CCH2), 28.7 (CCH CH ), 31.0
2 2
ar ar
ar
ar
ar-
C HC HC ), 131.6 (2C, NCCCH), 133.1 (SC ), 141.1
(CH CH CH Br), 32.3 (CH CH Br), 33.5 (CH Br), 121.8
2 2 2 2 2 2
ar
ar
ar
ar
(
(
2C, NCCCH), 144.8 (NCCCH ), 145.76 (H CC ), 154.7
(2C, CCHC), 131.5 (2C, NCCCH ), 140.4 (2C, NCCCH),
2
3
ar
2
2C, NCCH) ppm; 19F NMR (470 MHz, CD Cl ): δ =
146.0 (NCCCH ), 154.1 (2C, NCCH) ppm; F NMR
19
2
2
2

Medicinal Chemistry Research
(
470 MHz, CDCl ): δ = −147.1 to −146.1 (m) ppm; 11B
1571, 1527, 1488, 1477, 1438, 1395, 1366, 1352, 1322,
3
−1
NMR (160 MHz, CDCl ): δ = −2.16 (t, J = 33.0 Hz) ppm;
M (C H BBrF N ) = 396.11. MS (CI, CH ) m/z (%):
3
1274, 1250, 1199, 1182, 1162, 1146, 1104, 1081, 1033 cm ;
3
+
1
H NMR (400 MHz, DMSO-D6, TMS): δ = 1.40 (d, J =
1
8
24
2
2
5
+
+
97.15 (33, [M+H] ), 379.15 (100); HRMS (EI+): M
13.3 Hz, 2H), 2.37 (td, J = 4.6/13.3 Hz, 2H), 3.10–3.31 (m,
2H), 3.72 (s, 3H), 3.89 (dd, J = 12.3/4.2 Hz, 2H), 5.00 (s,
calc. for C H BBrF N , 396.1179; found: 396.1174.
1
8
24
2
2
1H), 5.06–5.17 (m, 2H), 6.90–6.99 (m, 2H), 7.18–7.25 (m,
5
4
,5-Difluoro-10-(3-hydroxypropyl)-1,3,7,9-tetramethyl-5H-
λ ,5 λ -dipyrrolo[1,2-c:2',1'-f][1,3,2]diazaborinin-4-ium-5-
1H), 7.28–7.43 (m, 5H), 7.58 (dd, J = 1.7/7.7 Hz, 1H) ppm;
4
4
13
C
NMR (100 MHz, DMSO-D6): δ = 34.2 (2C,
uide (19) BODIPY 18 (1.88 g, 4.13 mmol) was dissolved
NCH CH C), 40.0 (2C, NCH CH C), 55.2 (H CO), 65.8
2
2
2
2
3
in CH Cl (40.0 mL) and MeOH (20.0 mL) and LiOH
(CCH O), 70.1 (CH CCH ), 115.7 (CC C C H), 120.1
2 2 2 ar ar ar
2
2
(
237 mg, 9.91 mmol) dissolved in H O (10.0 mL) was
(C C HC HC H), 126.3 (CC C H), 127.3 (C C HC H-
ar ar ar ar ar ar ar ar ar
2
added dropwise. The reaction mixture was stirred at room
temperature for 4 h, and the solvent was removed. The
remaining residue was dissolved in EtOAc and washed with
H O and brine. The organic phase was dried with Na SO ,
C H), 127.7 (CC C HC HC HC HC ), 127.9 (2C,
ar ar ar ar ar ar ar
CC C HC H), 128.3 (2C, C C HC HC H), 135.9
ar ar
ar
ar ar
ar
ar
(CH CC ), 137.2 (OCH C ), 154.5 (OCN), 156.0
2
ar
2 ar
(H COC ) ppm; M (C H NO ) = 341.16 MS (FAB,
2
2
4
3
ar
20 23
4
+
+
filtered, and the solvent was removed to gain pure 19.
.21 g (96%); orange solid; mp 188–190 °C; IR (KBr)
νmax 3560, 3374, 2954, 2869, 1549, 1508, 1473, 1409,
NBA) m/z (%): 342.5 (MH ); HRMS (FAB, NBA): MH
1
calc. for C H NO , 342.1700; found: 342.1711.
2
0
24
4
1
1
368, 1305, 1268, 1225, 1202, 1161, 1134, 1102, 1078,
Biological evaluation
−
1 1
056 cm ; H NMR (400 MHz, CD Cl , TMS): δ = 1.62
2
2
(
t, J = 4.9 Hz, 1H), 1.77–1.90 (m, 2H), 2.44 (s, 6H), 2.47 (s,
MS Binding Assay
6
6
H), 3.02–3.09 (m, 2H), 3.77 (dd, J = 5.7/10.9 Hz, 2H),
1
3
.09 (s, 2H). C NMR (100 MHz, CD Cl , TMS): δ = 14.6
The MS Binding Assays were performed with mGAT1
membrane preparations obtained from a stable HEK293 cell
line and NO711 as non-labeled marker in competitive
binding experiments as described previously (Zepperitz
et al. 2006).
2
2
(
(
4C, NCCH ), 16.7 (CCH ), 25.5 (CH CH O), 34.8
3 2 2 2
CH CH O), 62.7 (CH O), 122.0 (2C, CCHC), 131.8 (2C,
2
2
2
NCC) 141.3 (2C, NCCCH), 146.9 (NCCCH ), 154.2
2
1
9
(
NCCH) ppm; F NMR (470 MHz, CD Cl ): δ = −146.1
2 2
11
to −146.7 (m) ppm; B NMR (160 MHz, CD Cl ): δ =
2
2
−
2.25 (t, J = 33.0 Hz, H) ppm; M (C H BF N O) =
GABA uptake assay
16
21
2
2
+
+
3
2
3
06.17. MS (CI, CH ) m/z (%): 307.15 (17, [M+H] ),
87.15 (100); HRMS (EI+): M calc. for C H BF N O,
06.1710; found: 306.1718.
5
+
3
The [ H]GABA uptake assays were performed in a 96-well
16
21
2
2
plate format with intact HEK293 cells stably expressing
mGAT1, mGAT2, mGAT3, and mGAT4, respectively, as
described earlier (Kragler et al. 2008).
Benzyl 4-hydroxy-4-(2-methoxyphenyl)piperidine-1-carbox-
ylate (22) 2-Bromanisole (6.0 µl, 4.82 mmol) was added to
Mg turnings (680 mg, 28.0 mmol) covered with dry THF
(
6.0 ml) and stirred vigorously at room temperature. After
Results and discussion
the Grignard reaction was finished, the reaction mixture was
stirred for another 30 minutes. To this reaction mixture N-
benzyloxycarbonyl-4-piperidone (20, 1.00 g, 4.29 mmol),
solved in dry THF (3.00 ml) was added dropwise, and the
mixture was stirred for 1 h at room temperature. The excess
Mg turnings were removed by filtration through cotton
wool, the reaction was quenched with addition of 2 N HCl
Synthesis of the ligands
In general, as indicated above, fluorescent GAT inhibitors
should be accessed by reaction of selected cyclic amines 7a-
l with the corresponding BODIPY dyes with an alkyl resi-
due in meso-position provided with a terminal leaving
group. The required BODIPY dyes with ω-halo-alkyl-
chains of different lengths, i.e. with a propyl, butyl, or
pentyl residue originating from the meso-position were
synthesized in the form of their chlorides [15a and 16
(Groom et al. 2016)] or bromides (17). These syntheses
were accomplished by following the general method shown
in Scheme 1. In the first step, 2,4-dimethylpyrrole (11) was
subjected to an acid catalyzed condensation reaction with
acid chlorides 12–14 to give the corresponding
(
7.00 mL), and extracted three times with Et O. The Et O
2 2
extract was washed with brine, dried over MgSO , filtered,
4
and the solvent was removed. The remaining residue was
purified by flash-chromatography (n-pentane/EtOAc 3:1,
1
% NEt3).
.10 g (76%); yellow solid; mp 101–104 °C; DC: R =
1
f
0
3
2
.38 (EtOAc/n-pentane = 1:3, 1% NEt ); IR (KBr) ν
448, 3076, 3034, 3009, 2998, 2959, 2934, 2916, 2839,
025, 1981, 1963, 1945, 1907, 1879, 1822, 1665, 1598,
3
max

Medicinal Chemistry Research
15a: n = 1, X = Cl, 39%
16: n = 2, X = Cl, 46%
17: n = 3, X = Br, 49%
11
12: n = 1, X = Cl
13: n = 2, X = Cl
4: n = 3, X = Br
1
18
19
15b
Scheme 1 : Synthesis of the BODIYs 15–17 and 15b
dipyrromethene intermediate which without prior isolation
was transformed into the required BODIPY dyes 15a, 16–
For the construction of the target compounds, the fluor-
escent ligands 8a-m–10a-m, in addition, the cyclic amine
moieties 7a-l shown in Fig. 2 were required. The cyclic
amines 7a-g as well as 7j and 7l were commercially
available. Compound 7i was synthesized as described in
literature (Haradahira et al. 2002) and for the synthesis of its
analogue 7h with a 2-methoxy substituted phenyl residue,
the same synthetic pathway was used, but (4-methyox-
yphenyl)magnesiumbromide was replaced by (2-methox-
1
7 in moderate yields of 39 to 49% upon complexation with
trifluoroboron etherate under basic conditions. Alternative
synthetic procedures reported previously for compounds
1
5a and 16 gave, in contrast to our synthesis, lower yields
and inseparable product mixtures, respectively (Esfandiari
et al. 2010; Kamkaew and Burgess 2013). In the course of
the synthesis of the new fluorescent ligands, nucleophilic
substitution reaction of propylchloride derivative BODIPY
yphenyl)magnesium
bromide
(21).
Hence,
the
1
5a with cyclic amines were found to give low yields only.
carbobenzoxy protected piperidone 20 was treated with
Grignard reagent 21 resulting after aqueous workup in the
addition product 22 which upon hydrogenerative removal of
To overcome this problem, the chloride function in 15b
should be replaced by a tosyloxy moiety which is known to
be a better leaving group resulting in meso-propyl BODIPY
dye 15b. For the synthesis of 15b, BODIPY 18 prepared
according to literature (Simonin et al. 2012) was subjected
to basic hydrolysis (LiOH) to give 19 in almost quantitative
yields. Here, the usage of LiOH was found to be essential
since the application of bases with different counter ions
such as sodium or potassium leads to the destruction of the
boron complex (Smithen et al. 2012). Compound 19 was
finally treated with tosylchloride in the presence of DMAP
the protective group (H , Pd-C) gave the secondary cyclic
2
amine 7h in quantitative yield (Scheme 2). The synthesis of
cyclic amine 7j started from the N-Boc protected piperidine
derivative 23 that had been accessed by a method described
in a patent (Castelhano et al. 2002). For the removal of the
N-Boc protective group from 23, the reported reaction
conditions were slightly varied (Castelhano et al. 2002).
Instead of the described sulfuric acid in methanol hydro-
chloric acid in diethyl ether was used (Scheme 2). Upon this
modification, the yield for the cleavage product 7j increased
and NEt to give 15b in a very good yield (94%, Scheme 1).
3

Medicinal Chemistry Research
Fig. 2 Structures of the used cyclic amines (7a–m) and the new BODIPY dyes 8a–m, 9a–m, and 10a–m
from 52 to 96%, whereas the reaction time decreased from
3
.5 days to 20 h (Scheme 2).
The first potential BODIPY derived GAT inhibitors were
synthesized by reacting 15a with four different amines, 7a,
b, 7h, and 7i, respectively, in the presence of K CO and
KI, for an in situ Finkelstein reaction in acetone under
microwave heating. The reaction resulted in low to good
yields varying from 32% (8a), 54% (8b), 44% (8h) to 70%
7
2
3
21
(
2
8i), respectively (Table 1, method A, entry 1, 5, 23, and
6). Due to low yields observed in some cases, the BOD-
IPY dye derived tosylate 15b should be used instead of the
chloro derivative 15a for the subsequent reactions with
remaining amines 7c–g and 7j–l. For comparative purposes,
the first reaction of tosyl derivative 15b was performed with
piperidine (7a) in acetonitrile at 50 °C of which 3 equiva-
lents were employed for the neutralization of acid formed
during the reaction. As compared to the alkylation reaction
with the chloro derivative 15a, the yield with tosylate 15b
rose from 32 to 80% (compare Table 1, entry 1 and 2)
indicating that the lower yields that had been obtained with
20
22
7h
23
7j
1
5a are due to the lower reactivity of the latter. Here and in
all subsequent alkylation reactions, acetonitrile instead of
acetone was used as solvent due to better solubility of the
reactants as for example of 15b. Hence, the synthesis of
target compounds 8c–g and 8j–l was accomplished by
reacting the remaining amines 7c–g and 7j–l with tosylate
Scheme 2 Synthesis of Amine 7h and 7j
7a–l in acetonitrile at 80 °C in the presence of K CO and
2
3
KI in acetonitrile (Table 1, method D), good yields ranging
from 74 to 91% for 9a–l could be achieved (Table 1,
method D, entry 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, and
36). The ligands with a pentyl spacer 10a–l were synthe-
sized by reaction of BODIPY 17 with 1.4 equivalents of the
corresponding amines 7a–l in acetonitrile at 80 °C in the
presence of K CO (Table 1, method C). Though KI was
1
7
5b under standard conditions resulting in good yields of
5–88% (Table 1, method B, entry 8, 11, 14, 17, 20, 29, 32,
and 35). In case of the synthesis of the florescent ligands
with a butyl spacer 9a–l, BODIPY 16 exhibiting chloride as
leaving group worked well as alkylating agent. Upon
reaction with 1.4 equivalents of the corresponding amines
2
3

Medicinal Chemistry Research
Table 1 Synthesis of the fluorescent ligands for mGAT1–mGAT4
omitted in this case because of the presence of bromide as
leaving group in 17, yields amounted to satisfying 56–95%
(
3
Table 1, entry 4, 7, 10, 13, 16, 19, 22, 25, 28, 31, 34, and
7).
To obtain compounds 8m–10m exhibiting a free nipe-
cotic acid function for the biological testing, the ester
function in 8l, 9l, and 10l had to be hydrolyzed which was
accomplished under basic conditions using LiOH in H O
2
providing the target compounds in yields of 71–85%
Entry
BODIPY
Amine
Product
Yield [%]
(Scheme 3). Again, LiOH was used as base to avoid
15aa
15bb
16c
17d
15aa
16c
17d
15bb
16c
17d
15bb
16c
17d
15bb
16c
17d
15bb
16c
17d
15bb
16c
17d
15aa
16c
17d
15aa
16c
17d
15bb
16c
17d
15ab
16c
17d
decomposition of the boron complex otherwise observed
when sodium or potassium containing bases were employed
1
2
3
4
5
6
7
8
9
7a
8a
32
80
86
78
54
78
82
81
81
58
82
74
80
88
86
87
75
40
72
87
78
87
44
81
73
70
74
56
75
91
83
88
82
77
79
80
95
- " -
- " -
- " -
7b
8a
(Smithen et al. 2012).
9a
10a
8b
9b
10b
8c
Biological evaluation
- " -
- " -
7c
For the synthesized fluorescent ligands 8a–k, 8m, 9a–m,
and 10a–m, the binding affinities for mGAT1 were deter-
mined in MS Binding Assays with NO711 as MS marker
- " -
- " -
7d
9c
(Zepperitz et al. 2006). In addition, these compounds were
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
10c
8d
9d
10d
8e
characterized with regard to their inhibitory potency at the
GABA transporter subtypes mGAT1–mGAT4 using a
3
- " -
- " -
7e
standardized [ H]GABA uptake assay which is based on
HEK cell lines, stably expressing the individual GATs
(
Kragler et al. 2008). If NO711 binding in MS Binding
3
3
- " -
- " -
7f
9e
Assays or [ H]GABA uptake in [ H]GABA uptake assays
was decreased by at least 50% at a concentration of 100 µM,
affinities (pK values) or the inhibitory potencies (pIC
10e
8f
i
50
- " -
- " -
7g
9f
values) were determined in additional experiments. When
compounds were not able to decrease NO711 binding or to
10f
8g
3
reduce [ H]GABA uptake to a value below 50% due to low
potency at the test concentration of 100 μM, only the per-
- " -
- " -
7h
9g
3
centage of remaining NO711 binding and [ H]GABA
10g
8h
9h
10h
8i
uptake, respectively, is given. In the following discussion,
3
remaining NO711 binding ≥ 50% or [ H]GABA uptake ≥
- " -
- " -
7i
50% given in Table 2 will be considered as being equal to a
pK ≤ 4 and pIC ≤ 4, respectively.
i
50
All tested compounds showed weak to mediocre inhibi-
tory potencies at the GABA transporters mGAT1–mGAT4
- " -
- " -
7j
9i
10i
8j
(Table 2). In comparison to the lead structures Tiagabine (1)
and SKF 89976-A (2), both known mGAT1 selective
inhibitors, the potencies at mGAT1 (pIC50 values) of the
new test compounds are low. Compound NNC 05-2090 (3)
has been reported in literature as mGAT2 selective and
NNC 05-2045 (4) has been reported in literature displaying
some selectivity for mGAT2 and to a low extent for
mGAT4 (Thomsen et al. 1997). According to own test
results, their potencies at mGAT1–mGAT4 are, however,
either rather similar for all four GATs (3) or for
mGAT2–mGAT4 (4), with a slight preference for the latter
as compared to mGAT1. Also, the pIC50 values of the new
test compounds at mGAT1–mGAT4 are quite similar,
which might be owed to the fact that these compounds show
- " -
- " -
7k
9j
10j
8k
9k
10k
8l
- " -
- " -
7l
15bb
16c
17d
- " -
- " -
9l
10l
aMethod A: 1.4 eq. of 7a-l, acetone, K2CO3, KI, 100 °C (Microwave)
bMethod B: 3.0 eq. of 7a-l, acetonitrile, 50 °C
c
Method D: 1.4 eq. of 7a-l, acetonitrile, K CO , KI, 80 °C
dMethod C: 1.4 eq. of 7a-l, acetonitrile, K2CO3, 80 °C
2
3

Medicinal Chemistry Research
Scheme 3 Hydrolysis of the
ester function in BODIPY 8–10l
using LiOH (aq.) to obtain the
nipecotic acid derivatives 8–
1
0m
8
9
l
l
n = 1
n = 2
8m n = 1
9m n = 2
10m n = 3
1
0l n = 3
some structural similarities to these two compounds. Inter-
estingly with regard to SNAP-5114 (5), a mGAT4 selective
compound, some of our test compounds reach pIC50 values
that are just half a log unit lower at mGAT4 than that of the
reference compounds. For compounds 8a, 9a, and 10a
for all transporter subtypes (Table 2, entry 12, n = 1). Also
compound 9g with a one carbon atom extended linker has
pIC50 values close to 5.00 at both mGAT2 and mGAT3
(Table 2, entry 12, n = 2). And furthermore, compound 10g
with a pentyl linker exhibited pIC50 values around 5.00 at
mGAT2 and mGAT4 (Table 2, entry 12, n = 3). Yet still no
distinct preference towards one GAT subtype can be
observed. For the compounds 8h, 9h, and 10h with the
cyclic amine subunit identical to that of NNC05-2090 (3),
we found moderate pIC50 values at all transporter subtypes
ranging from 4.72 to 5.20 (Table 2, entry 13). Although we
could not detect subtype selectivity for one of the trans-
porters mGAT1–mGAT4, but for mGAT2–4, we could
again observe that a longer linker is more favorable for
higher potencies. The compounds with the methoxy group
in 4-position of the phenyl ring attached to the piperidine
moiety, compounds 8i, 9i, and 10i (Table 2, entry 14) show
comparable pIC50 values for mGAT2–4 in the individual
linker series, whereby the inhibitory potencies increase with
increasing spacer length, leading to pIC50 values around 5
for 10i. Compounds 8j, 9j, and 10j with a phenyl group,
and also a chloride in 4-position of the phenyl ring attached
to the piperidine ring have some of the best pIC50 values at
mGAT1–mGAT4 of the compounds presented in this study
(Table 2, entry 15). Compound 8j with only a propyl linker
reached pIC50 values close to 5.00 for mGAT1 and even
higher pIC50 values for mGAT2. At mGAT3 and mGAT4,
(
Table 2, entry 6), with a pure piperidine ring as polar head,
which can be seen as starting point of the series of com-
pounds presented in this paper, inhibitory potencies ranging
from pIC50 ≤ 4.0 to almost 5.0 at the transporter subtypes
mGAT1–mGAT4 can be observed. Thereby, the test results
suggest that a spacer length of five carbon atoms seems to
be favorable for the inhibitory potency since compound 10a
has pIC50 values > 4.00 at all subtypes, mGAT1–mGAT4,
and a pIC50 value close to 5.00 at mGAT2 and neither 8a
nor 9a reach similar high values. Yet, none of these three
compounds show a distinct preference towards one of the
transporter subtypes (Table 1, entry 6). For a morpholine
ring containing compounds 8b, 9b, and 10b (Table 2, entry
7
)
only barely measurable inhibitory potencies at
mGAT1–mGAT4 can be observed. Yet again, compound
0b with the pentyl spacer has the highest inhibitory
1
potencies of these a morpholine ring containing com-
pounds. For the next series of compounds 8c, 9c, and 10c as
well as 8d, 9d, and 10d (Table 2, entry 8 and 9) with a
hydroxyl group in 3- or 4-position of the piperidine core,
the measured pIC50 values are in the range of pIC50 ≤ 4.00
to 4.69. For these compounds, the previously made obser-
vation that a pentyl linker is more favorable for the inhi-
bitory potency is no longer apparent. Also, a preference for
one of the four transporter subtypes was not noticeable for
any of these compounds. With the steric more demanding
yet more lipophilic amines 8e, 9e, and 10e as well as 8f, 9f,
and 10f (Table 2, entry 10 and 11) exhibiting a phenyl
residue at the piperidine ring, again only weak to mediocre
inhibitory potencies with no notable subtype selectivity are
observed. For compounds 8g, 9g, and 10g exhibiting not
only a phenyl group, but also an additional hydroxyl group
in 4-position of the piperidine ring, the test results
improved. Compound 8g with a spacer length of three
carbon atoms displays pIC50 values ranging from 4.41–4.86
the pIC50 were lower with pIC = 4.79 at mGAT3 and
50
pIC = 4.83 at mGAT4 (Table 2, entry 15, n = 1). Com-
5
0
pound 9j with the butyl linker has pIC50 values close to or
higher than 5.00 for all four transporter subtypes (Table 2,
entry 15, n = 2). For compound 10j with the pentyl linker,
we found the highest measured pIC50 values in this study at
mGAT2–4, ranging from 5.12 ± 0.08 to 5.35 ± 0.04. Only at
mGAT1, the measured pIC50 value was less than 5.00
(pIC = 4.90, Table 2, entry 15, n = 3). As for the com-
5
0
pounds with the methoxy groups, also the position of the
chloride from the 2-position to the 4-position of the phenyl
ring has been altered. For the compounds with a methoxy
group and a butyl or pentyl spacer, i.e. compounds 9h, 9i,

Medicinal Chemistry Research
Table 2 GABA-uptake inhibition

Medicinal Chemistry Research

Medicinal Chemistry Research
aResults are given as pKi ± SEM of three independent experiments, each performed in triplicate. For low pKi values only one measurement was
performed in triplicate, therefore no SEM was calculated or only the percentage of remaining MS Marker Binding at a concentration of 100 μM has
been determined
b
3
Results of [ H]GABA uptake assays are given as pIC50 ± SEM of three independent experiments, each performed in triplicate. For low pIC50
3
values only one measurement was performed in triplicate, therefore no SEM could be calculated. Percentages represent remaining [ H]GABA
uptake in the presence of 100 µM test compound
cpIC50 values were determined using the same standard assay as for all tested compounds (Kragler et al. 2008)
d
e
not determined tested as hydrochloride
1
0h, and 10i, it had been found that the position of the
compounds 8m, 9m, and 10m with the nipecotic acid as
methoxy group (2- and 4-position) has just little influence
on the pIC50 values (Table 2, entry 13 and 14). For com-
pounds 8k, 9k, and 10k with a chloride instead of a
methoxy group (Table 2, entry 16), the position of the
chloride has some impact on the uptake inhibition as
compared to the inhibitory activity of regioisomers 8j, 9j,
and 10j. Compound 8k with a chloride in 4-position of the
phenyl ring and a propyl linker reached pIC50 values
slightly higher than 5.00 just for mGAT2 and mGAT4
cyclic amine adapted from Tiagabine, which has a pK value
of 7.43 (Table 2, entry 1) have just weak binding affinities
i
(pK = 4.22–4.48, Table 2, entry 18, n = 1–3). Only
i
exceptions are compounds 9j and 10j, respectively, pre-
senting a higher binding affinity towards mGAT1 with pKi
values higher than 5.00 (Table 2, entry 15) representing
with compound 8j the most potent inhibitors at mGAT1
(see Table 2, entry 15, pIC = 5.27 ± 0.05) in this study.
50
For all compounds studied, the found pK values for
i
(
Table 2, entry 16, n = 1), which is still close to the values
mGAT1 in MS Binding Assays were similar or about a half
log unit higher than the pIC50 values observed in [ H]GABA
uptake assays, which is a common phenomenon frequently
observed with the used test system (Zepperitz et al. 2006).
3
observed for 8j. Compound 9k with the butyl linker has
clearly decreased pIC50 values compared to compound 9j
with pIC50 values ranging from pIC50 ≤ 4.00 to 4.85 (Table
2
, entry 15 and 16, n = 2). Compound 10k with a pentyl
linker has an almost identical pIC50 of 5.30 ± 0.07 as 10j
pIC = 5.35 ± 0.04) at mGAT2 and for the other trans-
The data for the binding affinities (pK ) and inhibitory
i
potencies (pIC ) are thus fitting very well.
50
(
5
0
porter subtypes mGAT1 and mGAT3–mGAT4 pIC50 values
of 4.96 for mGAT1 and values close to 5.00, but yet less
than the values measured for its analogue with the chloride
in 2-position, compound 10j (Table 2, entry 15 and 16, n =
Conclusion
In conclusion, a series of novel fluorescent ligands deli-
neated from common GAT inhibitors in which the lipo-
philic domain has been replaced by a BODIPY dye subunit
has been synthesized and evaluated for binding affinities at
mGAT1 and inhibitory potencies at mGAT1–mGAT4.
Overall, the inhibitory potencies of the presented com-
pounds were weak to mediocre, and no distinct selectivity
towards one transporter subtype was observed. Still, some
of the herein presented compounds show pIC50 values of up
to 5.35 at different transporter subtypes, whereby highest
potencies are observed for mGAT2–4. Additionally, two of
3
). The biological evaluation of 9l and 10l, both ester pre-
cursors of nipecotic acid, resulted in pIC50 values > 4.5 at
mGAT1–mGAT4 with the highest pIC50 value of 5.05 ± 0.2
exhibited by compound 10l at mGAT3 (Table 2, entry 17,
n = 3). Fluorescence ligands 9m–10m characterized by a
nipecotic acid subunit (Table 2, entry 18, n = 1, 2 and 3) as
e.g. in Tiagabine (1) showed, independent from the length
of the linker, no noticeable inhibitory potency at any of the
transporter subtypes mGAT1–mGAT4 (Table 2, entry 18).
In summary, it can be concluded by the obtained data that in
general longer spacers and the usage of more lipophilic and
sterically more demanding cyclic amines are favorable for
higher pIC50 values, when a BODIPY core is used as a
substitute for the aromatic domain found in most common
GAT inhibitors such as 1–5 that consist of two or more aryl
rings or a carbazole unit.
the compounds have pK values above 5.00 at mGAT1.
i
Although the best inhibitors lack a distinct subtype selec-
tivity, the measured pIC50 values and subtype selectivities
are in the same range as those of the prototypic inhibitors of
mGAT2-mGAT4, i.e. of NNC 05-2090 (3), NNC 05-2045
(4), and (S)-SNAP-5114 (5). This study sheds light on the
effect that the structure of the amine subunit of the target
compounds and the length of the spacer have on the inhi-
bitory potency at the GABA transporter. In particular, a
spacer with four to five carbon atoms in combination with a
4-hydroxy-4-phenyl-piperidine moiety carrying a methoxy
or chloro substituent at the aromatic residue representing the
amino subunit seems to be favorable for reasonable
In addition to the pIC50 values, also the binding affinities
of the synthesized compounds at mGAT1 were determined.
Almost all compounds of this study show, independent of
the cyclic amine subunit present and the length of the spacer
(
three to five carbon atoms), low to negligible binding
affinities for mGAT1 with pK values ranging from below
i
4
.00 to 4.73 (Table 2, entry 6–14 and 16–18). Even

Medicinal Chemistry Research
inhibitory potencies at the GABA transporter. As fluores-
cence based analysis techniques not necessarily require
ligands with high binding affinity to the target, the herein
presented fluorescent GAT inhibitors might serve as pro-
mising tool compounds or at least as a starting point for the
development of such entities for the respective analytical
methods.
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Conflict of interest None of the authors have conflict of interest related
to the information described in this paper.
Publisher’s note Springer Nature remains neutral with regard to
jurisdictional claims in published maps and institutional affiliations.
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