Synthesis of fluorescent ring-fused 2-pyridone peptidomimetics

Article abstract of DOI:10.1021/jo401844y

Thiazolino fused 2-pyridone peptidomimetics are of significant biological importance due to their ability to interfere with adhesive fiber formation in uropathogenic Escherichia coli and oligomerization of amyloid fibers. We have developed an efficient synthetic route to fluorescent BODIPY analogues, with structural diversification from a key intermediate enabling introduction of C-2 substituents and late incorporation of the BODIPY moiety. A mild lithium halide mediated hydrolysis enabled preparation of peptidomimetic fluorophores with useful photophysical properties for further chemical biology applications.

Full text of DOI:10.1021/jo401844y

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Note
Synthesis of fluorescent ring-fused 2-pyridone peptidomimetics
K. Syam Krishnan, Christoffer Bengtsson, James A. D. Good, Shamil
Mirkhanov, Erik Chorell, Lennart B.-Å. Johansson, and Fredrik Almqvist
J. Org. Chem., Just Accepted Manuscript • Publication Date (Web): 25 Oct 2013
Downloaded from http://pubs.acs.org on October 29, 2013
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Synthesis of fluorescent ringꢀfused 2ꢀpyridone peptidomimetics
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K. Syam Krishnan,1 Christoffer Bengtsson,1 James A. D. Good,1,2 Shamil Mirkhanov,1 Erik
Chorell,1 Lennart B. –Å. Johansson,1 Fredrik Almqvist.*,1,2
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1 Umeå University, Department of Chemistry, 901 87 Umeå, Sweden; 2 Umeå Centre for Microbial
Research, Umeå University, 901 87 Umeå, Sweden.
* Corresponding author: Prof. Fredrik Almqvist, Department of Chemistry, Umeå University SEꢀ
90187 Umeå, Sweden; Fax: (+46)907867655; Email: fredrik.almqvist@chem.umu.se
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Graphical Abstract
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Abstract
Thiazolino fused 2ꢀpyridones peptidomimetics are of significant biological importance due to their
ability to interfere with adhesive fiber formation in uropathogenic Escherichia coli and
oligomerization of amyloid fibres. We have developed an efficient synthetic route to fluorescent
BODIPY analogues, with structural diversification from a key intermediate enabling introduction
of Cꢀ2 substituents and late incorporation of the BODIPY moiety. A mild lithium halide mediated
hydrolysis enabled preparation of peptidomimetic fluorophores with useful photophysical
properties for further chemical biology applications.
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Antibiotics represent one of the greatest innovations in medicine, but the emergence of widespread
resistance has precipitated an urgent need for new therapeutic strategies. Peptidomimetic ringꢀ
fused 2ꢀpyridones represent a promising class of compounds that can disrupt virulence in
uropathogenic Escherichia coli (UPEC), a causative agent of urinary tract infection (UTI).1 In their
colonization of the urinary tract, a variety of extracellular fibers are utilized by UPEC in order to
adhere to host cells.2 The formation of one of the primary types of these adhesive fibers, typeꢀ1
pili, is disrupted by ringꢀfused 2ꢀpyridones termed pilicides (1ꢀ4, Figure 1).3
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FIGURE 1 – Representative peptidomimetic thiazolo 2ꢀpyridones 1ꢀ4 and fluorescent analogue 5.
The IC50 refers to piliꢀdependent biofilm formation in the clinical UPEC isolate UTI89, while ΦF
refers to the quantum yields.4,5
Introducing bulkier substituents in the Cꢀ8 position produces analogues which inhibit formation of
another type of fiber in UPEC, curli.6 These functional amyloid fibers are employed by UPEC in
forming biofilms, which are implicated in the pathogenesis of recurrent and serious UTIs.6
Significantly, thiazolino 2ꢀpyridone analogues also interfere with the oligomerization of
neurodegenerative associated amyloid fibres.7,8 These peptidomimetics are therefore of significant
interest as chemical biology tools and for potential therapeutic applications.
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Fluorescent probes are essential tools in gaining insight into cellular and bacterial environments,9,10
and previously we developed dihydrothiazoloꢀfused 2ꢀpyridones containing BODIPY fluorophores
in the Cꢀ7 or Cꢀ8 position (e.g. 5, Figure 1).5 Initial evaluations revealed 5 possessed useful
photophysical properties and promising efficacy in halting biofilm formation in the clinical UPEC
strain UTI89.5 We were interested to develop further BODIPY analogues that incorporated Cꢀ2
substituents, as these are known to improve activity against piliꢀdependent biofilm formation (1ꢀ4,
Figure 1).4 In this paper, we present an expedient synthesis to BODIPY containing ringꢀfused 2ꢀ
pyridones, which allows introduction of diverse Cꢀ2 substituents through a key intermediate, and
late introduction of the sensitive BODIPY moiety, thereby greatly increasing the overall efficiency.
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Initially, we attempted to prepare the Cꢀ2 substituted BODIPY analogues from the previously
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synthesized methyl ester 6,5 using a oneꢀpot procedure developed for this scaffold (Scheme 1).11
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SCHEME 1 – Oxidation/bromination of BODIPY derivative 6.
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However, we were unable to obtain 7 in yields > 20% due to the sensitivity of BODIPY to the basic
conditions. This inherent vulnerability of BODIPY to both basic and acidic reaction conditions is
well documented.12ꢀ14 In addition to providing a substantial impediment to the scope and success
of subsequent transformations, introducing the fluorophore at the outset of the synthesis was
inefficient due to the low yields in generating 6 (11% over three steps from succinic anhydride).5
We therefore envisaged preparing the Cꢀ2 substituted thiazolo 2ꢀpyridones from a key intermediate
containing a carboxylic acid substituent in the Rꢀ7 position to permit installation of the BODIPY
moiety at a later stage, and a bromine to enable functionalization of the Cꢀ2 position (e.g. 8,
Scheme 2).
SCHEME 2 ꢀ Synthesis of key 2ꢀbromo substituted intermediate 8.
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To access 8, we prepared the acylated Meldrum's acid derivative 10 from mono benzylated succinic
ester 9. Subsequent cyclocondensation of 10 with thiazoline 11 furnished the dihydrothiazolino 2ꢀ
pyridone 12 in 80% yield.15 While classical hydrogenation conditions to deprotect benzyl ester 12
proved sluggish, with only 50% conversion after 24 h with Pd/C or Pd(OH)2/C and 1 atm hydrogen
at rt in methanol, transfer hydrogenation with 1,4ꢀcyclohexadiene and Pd(OH)2/C was more
effective and provided the carboxylic acid 13 in 90% yield. We next attempted the oneꢀpot
oxidation/bromination of 13 using the previously developed conditions (3 eq. NaH, 3 eq. CCl3Br
and 2 eq. MeOH in CH3CN),11 but the poor solubility of 13 in acetonitrile prohibited success.
Switching to THF or CH2Cl2/MeOH mixtures afforded no improvement as we noted hydrolysis of
the methyl ester, while in DMF formylation occurred at Cꢀ6, in addition to the desired reaction.
However, using pyridine as the reaction solvent overcame these issues and the key 2ꢀbromothiazole
intermediate 8 was obtained in 80% yield.
The structural diversification of 8 was then investigated, firstly by Suzuki–Miyaura cross
couplings. Applying the method utilized in the derivatization of 4 (benzylboronic acid pinacol
ester, Pd(OAc)2, KF, MeOH and MWI at 100 °C, 10 min) afforded only limited conversion, so a
catalyst screen was undertaken.4 With the same procedure, no conversion was observed by LCꢀ
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MS using Pd(PPh3)4, while PEPPSIꢀIPr and PEPPSIꢀSIPr catalysts gave only dehalogenated 8.
Improved conversion was afforded by Pd(dppf)Cl2ꢁCH2Cl2, albeit with low isolated yield of 44%
and significant dehalogenation. However, upon switching from KF to K2CO3 a dramatic increase
in yield was obtained, with 14a isolated in 81% yield with Pd(dppf)Cl2ꢁCH2Cl2 and MWI for 12
min at 80 °C (Scheme 3).
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SCHEME 3 – Scaffold derivatization from 2ꢀbromo substituted 8.a
a
= Reagents and conditions: 14aꢀc: a) Pd(dppf)Cl2ꢁCH2Cl2 (10 mol%), RB(OH)2/pinacol ester,
K2CO3, MeOH, MWI, 80 °C, 12 min. 15: b) Phenylacetylene, Pd(Ph3P)2Cl2 (5 mol%), CuI (10
mol%), K2CO3, MWI , 80 °C, 10 min, 80%. 16: (c)(i) nꢀBuLi, ꢀ78 °C, 10 min; (ii) PhNCO, ꢀ70
°C, 15 min, 64%.
These conditions were also successful with phenyl and methyl boronic acids, with the respective
crossꢀcoupled products 14b and 14c each obtained in 79% yield. We next investigated the
Sonogashira coupling of 8 with phenylacetylene: in analogy with the Suzuki coupling, our
previously developed method was not successful (Pd(Ph3P)2Cl2, CuI and NEt3 in DMF with MWI
at 110 °C.16 However on exchanging the base for K2CO3, the acetylene substituted 15 was
obtained in 80% yield. Lithiation of the Cꢀ2 bromine was attempted next, with 2.0 eq. of n-BuLi at
ꢀ78 °C followed by addition of phenyl isocyanate. Pleasingly, this gave phenylamide 16 featuring
an extended peptidomimetic backbone in 64% yield. We noted that reaction with the electrophile
did not proceed unless a slight warming to ꢀ70 °C was allowed.
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The 2ꢀbromothiazole 8 proved an effective intermediate for structural elaboration, and we
proceeded to introduce the BODIPY fluorophore, by conversion to the acyl chloride, condensation
with pyrrole, and treatment of the dipyrromethene intermediate with BF3ꢁEt2O and NEt3.17
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TABLE 1 – Synthesis of new BODIPY derivatives and photophysical characterization.
Photophysical propertiesa
BODIPY
product
(yield%)
Hydrolysis
product
(yield%)
Bond
C2ꢀC3
Substrate
R
Hydrolysis method
λabs
λfl
τ
ΦF
(nm) (nm) (ns) (%)
LiOH, THF/MeOH,
rt, 2 h
LiBr, DMF, MWI,
90 °C, 70 min
LiI, DMF, MWI,
80 °C, 60 min
rac-6
(41%)
rac-18
(84%)
Single
H
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500
499
508
509
509
508
1.7
3.8
3.4
3.7
18
2
13
Double Bn 17a (33%)
Double Ph 17b (39%)
Double Me 17c (38%)
19a (65%)
19b (68%)
19c (55%)
14a
14b
14c
4
LiBr, DMF, MWI,
100 °C, 30 min
3
a = Measured in DMSO at concentrations of approx. 10ꢀ5 mol/L at 25 °C.
These conditions proved effective for all substrates examined, providing the BODIPY methyl esters
6 and 17aꢀ17c in good yields for this reaction; formation of the BODIPY moiety is known to be
challenging, and these yields represent a > 2ꢀfold improvement over comparable BODIPY forming
steps in our previous route,5 and compare favorably with the synthesis of other BODIPY
derivatized small molecules.18,19 We noted the Cꢀ3 stereocenter of dihydrothiazolo analogue racꢀ6
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was epimerized during BODIPY formation; however, both enantiomers in similar dihydrothiazolo
analogues display comparable efficacy in piliꢀdependent UPEC biofilm assays.20
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The carboxylic acid is an essential feature of biological activity in pilicides affecting UPEC
virulence,20 and the subsequent hydrolysis of the dihydrothiazolo racꢀ6 proceeded smoothly using
aqueous LiOH to afford carboxylate rac-18 in 81% yield.5 However, hydrolysis of the thiazolo
BODIPY methyl esters 17aꢀc proved challenging, and aqueous LiOH was ineffective. We
consequently examined a range of hydrolysis conditions with 17a as substrate (Supporting
Information, Supplementary Table 1), and identified lithium bromide halogenolysis as a mild and
efficient method to achieve this transformation: with LiBr (50 equiv.) in DMF and MWI at 90 °C
for 70 min, the desired carboxylic acid 19a was obtained in 65% yield. This method also proved
effective for 2ꢀmethyl substituted 17c, but less efficient for the 2ꢀphenyl substituted 17b, with only
23% yield of the corresponding carboxylic acid 19b obtained. Employing LiI as the halide source
resulted in an increased yield of 68%. The LiI mediated cleavage of methyl esters in DMF has
classically been applied to terpenoid derivatives, and to our knowledge this is the first time it has
been utilized for BODIPY methyl esters.21,22 Our initial evaluations with a range of BODIPY
derivatives suggest it may be more generally applicable as a mild method for ester removal
(Supporting Information, Supplementary Table 2).
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Evaluation of the photophysical properties of the new derivatives revealed that the dihydrothiazolo
analogue rac-18 possessed the highest quantum yield (ΦF = 18%, Table 1), with much lower values
recorded for the thiazolo derivatives 19aꢀc. All the compounds evaluated exhibited biphasic
fluorescence relaxation (exemplified by Figure S1, Supporting Information), with average lifetimes
ranging between 1.7 and 3.8 ns. If one assumes that the shortened lifetimes are due to dynamic
quenching, and one uses the known radiative lifetime of BODIPY,23 the expected quantum yields
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would range between 30ꢀ70 %. However, the experimental quantum yields were considerably
lower. Since the shapes of the recorded BODIPY absorption and fluorescence spectra were very
similar to those of free BODIPY, it is unlikely that static quenching caused by selfꢀaggregation of
the studied BODIPY derivatives provided the principle relaxation pathway.24 Instead, static
intramolecular quenching was probably the dominating relaxation path. A similar pattern was
observed with other solvents (CH3Cl and 1,2ꢀpropanediol), which supports the probability of
intramolecular quenching processes. We previously attributed the influence of the thiazolino
sulfur to the low observed quantum yields, since replacement with oxygen or a sulfoxide gave
BODIPY analogues with greatly improved quantum yields.5 Oxidation to the thiazole and
substitution in Cꢀ2 does not appear to negate this effect or provide photophysical improvements to
the observed quantum yields. However, the quantum yield of rac-18 improves considerably on the
most interesting fluorescent analogues from our previous study and indicates the Cꢀ8 cyclopropyl
may be beneficial to the photophysical properties over phenyl in this position (5, Figure 1).
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In summary, we have developed an expedient synthetic route to synthesize highly substituted
fluorescent dihydrothiazolo/thiazolo 2ꢀpyridone peptidomimetics. Comparison with our previous
route for preparation of dihydrothiazolo 6 confirms the improved efficacy of the new route (28% vs
11%; Supporting Information, Schemes S1 and S2). Elaboration from a key intermediate enabled
transition metal catalyzed CꢀC bond formation in the Cꢀ2 position with sp, sp2 and sp3 coupling
partners, while lithium halogen exchange made introduction of a new CꢀN bond possible to extend
the peptidomimetic backbone and develop important tools for further applications.
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Experimental Section
General
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All reagents and solvents were used as received from commercial suppliers, unless indicated
otherwise. CH2Cl2 and THF were dried in a solvent drying system (drying agent: neutral alumina)
and collected fresh prior to every reaction. Pyridine was dried over 4 Å molecular sieves. NaH
was prewashed with pentane, dried under vacuum, and stored in a dessicator. Microwave reactions
were performed using a Biotage Initiator microwave synthesizer in sealed vessels; temperatures
were monitored by an internal IR probe. TLC was performed on aluminum backed silica gel plates
(median pore size 60 Å, fluorescent indicator 254 nm) and detected with UV light at 254 nM.
Column chromatography was performed using silica gel with average particle diameter 50 ꢂM (range
40ꢀ65 ꢂM, pore diameter 53 Å) and eluents are given in brackets. Optical rotation was measured
with a polarimeter at 25 °C at 589 nm. IR spectra was recorded on a spectrometer equipped with
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1
an ATR device. H and 13C NMR spectra were recorded on a 400 MHz spectrometer at 298 K and
calibrated by using the residual peak of the solvent as the internal standard (CDCl3 : δH = 7.26 ppm;
δC = 77.16 ppm. DMSOꢀd6: δH = 2.50 ppm; δC = 39.50 ppm). HRMS was performed by using a
mass spectrometer with ESI ꢀ TOF (ES+); sodium formate was used as the calibration chemical.
Compounds 9 and 11 were synthesized according to literature procedures.25,26
4ꢀ(2,2ꢀDimethylꢀ4,6ꢀdioxoꢀ[1,3]dioxanꢀ5ꢀylidene)ꢀ4ꢀhydroxyꢀbutyric acid benzyl ester 10.
Succinic acid monobenzyl ester (5 g, 24 mmol), 2,2ꢀdimethylꢀ1,3ꢀdioxaneꢀ4,6ꢀdione (3.63 g, 25.2
mmol) and DMAP (4.7 g, 38.4 mmol) were dissolved in CH2Cl2 (125 mL) and the mixture was
cooled to 0 °C. DCC (6.4 g, 31.2 mmol) was dissolved in CH2Cl2 (15 mL) and added drop wise to
the solution. The reaction mixture was then left at rt overnight. The reaction was quenched with
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6% aq. KHSO4 and the resulting precipitate was filtered off. The filtrate was washed with 6% aq.
KHSO4 (3 80 mL), brine (80 mL), dried over Na2SO4, filtered and concentrated gave 9 (7.65 g,
×
7
8
9
95%) as a greenish viscous liquid and was used without further purification; Rf = 0.34 (CH2Cl2ꢀ
MeOH, 97/3); IR (υ cmꢀ1) (neat) 3320, 2927, 2850, 1731, 1656, 1571, 1382, 1269, 1155.; 1H NMR
(CDCl3, 400 MHz) δ (ppm) 15.59 (br s, 1H), 7.36ꢀ7.32 (m, 5H), 5.13 (s, 2H), 3.46 (t, 2H, J = 6.6
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13
Hz), 2.79 (t, 2H, J = 6.6 Hz), 1.72 (s, 6H); C NMR (CDCl3, 100 MHz) δ (ppm) 195.5, 171.6,
170.7, 160.3, 135.6, 128.6 (2C), 128.4, 128.3 (2C), 105.2, 91.7, 66.8, 30.9, 28.8, 26.8 (2C). HRMS
(EI): m/z: calcd for C17H18O7: 357.0950 [M+Na]; found: 357.0961.
7ꢀ(2ꢀBenzyloxycarbonylꢀethyl)ꢀ8ꢀcyclopropylꢀ5ꢀoxoꢀ2,3ꢀdihydroꢀ5Hꢀthiazolo[3,2ꢀa]pyridineꢀ3ꢀ
carboxylic acid methyl ester 12.
10 (1.6 g, 8.02 mmol) and 11 (6.1 g, 18.4 mmol) was dissolved in 1,2ꢀdichloroethane (32 mL) and
TFA (0.61 mL, 8.02 mmol) was added and reaction mixture was heated in the microwave oven at
120 0C for 140 seconds (The reaction was done in four different batches). The reaction mixture was
diluted with CH2Cl2 and washed with saturated NaHCO3 (aq), the organic phase was dried
(Na2SO4), filtered and concentrated. The crude material on purification by column chromatography
(heptane/EtOAc from 4/1 to 1/4) afforded 12 as a brown oil (2.65 g, 80%); Rf = 0.52 (EtOAc);
20
[α]D = ꢀ197.8 (c 0.7, CH2Cl2); IR (υ cmꢀ1) (neat) 2954, 1736, 1655, 1578, 1490, 1354, 1210,
1172; 1H NMR (CDCl3, 400 MHz) δ (ppm) 7.34ꢀ7.27 (m, 5H), 6.05 (s, 1H), 5.51 (dd, 1H, J = 2.4,
8.4 Hz), 5.08 (s, 2H), 3.73 (s, 3H), 3.58 (dd, 1H, J = 8.4, 11.6 Hz), 3.42 (dd, 1H, J = 2.4, 11.6 Hz),
3.05 ꢀ2.89 (m, 2H), 2.66ꢀ2.61 (m, 2H), 1.55 ꢀ1.47 (m, 1H), 0.92ꢀ0.81 (m, 2H), 0.60ꢀ0.53 (m, 2H));
13C NMR (CDCl3, 100 MHz) δ (ppm) 172.2, 168.7, 161.2, 156.3, 147.5, 135.8, 128.6 (2C), 128.3,
128.2 (2C), 113.4 (2C), 66.6, 62.8, 53.2, 32.9, 31.6, 27.6, 10.9, 7.7, 7.5; HRMS (EI): m/z: calcd for
C22H23NO5S: 436.1195 [M+Na]; found: 436.1204.
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7ꢀ(2ꢀCarboxyꢀethyl)ꢀ8ꢀcyclopropylꢀ5ꢀoxoꢀ2,3ꢀdihydroꢀ5Hꢀthiazolo[3,2ꢀa]pyridineꢀ3ꢀcarboxylic
acid methyl ester 13.
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To 12 (748 mg, 1.81 mmol) in 15 mL methanol was added Pd(OH)2/C (127mg, 0.18 mmol) and
1,4ꢀcyclohexadiene (2.57 mL, 27.2 mmol) while stirring. The mixture was refluxed at 65 °C for 12
h and then filtered on Celite®. Purification of the crude material by column chromatography
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(CH2Cl2ꢀMeOH 97/3 and CH2Cl2ꢀMeOHꢀAcOH 95/5/1, from 1/0 to 0/1) afforded 13 as a white
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solid (525 mg, 90%); Rf = 0.38 (CH2Cl2ꢀMeOHꢀAcOH, 95/5/1); [α]D
=
ꢀ205 (c 0.5,
CH2Cl2:MeOH 7:3); IR (υ cmꢀ1) (neat) 2962, 1753, 1714, 1631, 1553, 1495, 1345, 1285, 1207,
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1190; H NMR (CDCl3, 400 MHz) δ (ppm) 6.11 (s, 1H), 5.56 (dd, 1H, J = 2.0, 8.8 Hz), 3.77 (s,
3H), 3.74 (dd, 1H, J = 8.8, 12.0 Hz), 3.52 (dd, 1H, J = 2.0, 11.8 Hz), 3.09 ꢀ2.93 (m, 2H), 2.63ꢀ2.59
(m, 2H), 1.65 ꢀ1.58 (m, 1H), 1.02ꢀ0.88 (m, 2H), 0.67ꢀ0.58 (m, 2H)); 13C NMR (CDCl3, 100
MHz) δ (ppm) 174.7, 168.6, 162.1, 158.1, 148.7, 114.9, 112.5, 63.1, 52.8, 32.7, 31.2, 27.6, 10.7,
7.4, 7.2; HRMS (EI): m/z: calcd for C15H17NO5S: 346.0725 [M+Na]; found: 346.0750.
2ꢀBromoꢀ7(2ꢀcarboxyꢀethyl)ꢀ8ꢀcyclopropylꢀ5ꢀoxoꢀ5Hꢀthiazolo[3,2ꢀa]pyridineꢀ3ꢀcarboxylic
acid methyl ester 8.
NaH (229 mg, 9.56 mmol, washed with nꢀpentane) was added to a stirred solution of 13 (773 mg,
2.39 mmol) dissolved in 18 mL of dry pyridine at 0 °C. After 10 min, BrCCl3 (0.71 mL, 7.17
mmol) was added and the mixture was allowed to attain rt and stirred for an additional 10 min,
followed by the addition of dry methanol (0.15 mL, 3.60 mmol). After 4 h stirring at rt, the
reaction was quenched by dropwise addition of 6% aq. KHSO4. The solvent was removed under
reduced pressure, and the residue is dissolved in ethyl acetate and acidified. The organic layer was
washed with 6% aq. KHSO4 (3×) and brine, dried over Na2SO4, filtered and concentrated.
Purification by column chromatography (CH2Cl2ꢀMeOH 97/3 and CH2Cl2ꢀMeOHꢀAcOH 95/5/1,
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from 1/0 to 0/1) gave 8 as a pale yellow solid (768 mg, 80%); Rf = 0.44 (CH2Cl2ꢀMeOHꢀAcOH,
95/5/1); IR (υ cmꢀ1) (neat) 2949, 1747, 1714, 1629, 1541, 1474, 1432, 1330, 1247, 1168; 1H NMR
(CDCl3, 400 MHz) δ (ppm) 6.27 (s, 1H), 3.94 (s, 3H), 3.14 (t, 2H, J = 7.6 Hz), 2.70 (t, 2H, J = 7.6
Hz), 1.89 ꢀ1.82 (m, 1H), 1.14ꢀ1.08 (m, 2H), 0.78ꢀ0.69 (m, 2H)); 13C NMR (CDCl3, 100
MHz) δ (ppm) 175.9, 161.3, 159.8, 156.7, 148.8, 131.6, 115.1, 110.7, 106.0, 53.9, 33.9, 28.8, 11.6,
8.4 (2C); HRMS (EI): m/z: calcd for C15H14BrNO5S: 421.9674 [M+Na]; found: 421.9678.
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Typical procedure for Suzuki coupling
The procedure described for 14a is representative for SuzukiꢀMiyaura couplings.
2ꢀBenzylꢀ7ꢀ(2ꢀcarboxyꢀethyl)ꢀ8ꢀcyclopropylꢀ5ꢀoxoꢀ5Hꢀthiazolo[3,2ꢀa]pyridineꢀ3ꢀcarboxylic
acid methyl ester 14a
8 (227 mg, 0.567 mmol), benzyl boronic acid pinacol ester (0.12 mL, 1.42 mmol), Pd(dppf)2ꢁ
CH2Cl2 (46.3 mg, 0.056 mmol) and K2CO3 (391.8 mg, 2.84 mmol) was dissolved in MeOH (8.5
°
mL) and the reaction heated by MWI at 80 C for 12 min. The reaction mixture was diluted with
ethyl acetate and acidified. The organic layer was washed with water, brine, dried over Na2SO4,
filtered and concentrated. Purification by column chromatography (CH2Cl2ꢀMeOH 97/3 and
CH2Cl2ꢀMeOHꢀAcOH 95/5/1, from 1/0 to 0/1) gave 14a as a pale yellow solid (189 mg, 81%); Rf =
0.41 (CH2Cl2ꢀMeOHꢀAcOH, 95/5/1); IR (υ cmꢀ1) (neat) 2925, 1721, 1633, 1553, 1481, 1433, 1334,
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1191, 1008; H NMR (MeOD, 400 MHz) δ (ppm) 7.34ꢀ7.28 (m, 5H), 6.23 (s, 1H), 4.07 (s, 2H),
3.94 (s, 3H), 3.11 (t, 2H, J = 7.6 Hz), 2.66 (t, 2H, J = 7.6 Hz), 1.83 ꢀ1.75 (m, 1H), 1.07ꢀ1.01 (m,
13
2H), 0.68ꢀ0.63 (m, 2H)); C NMR (MeOD, 100 MHz) δ (ppm) 174.6, 161.3, 159.2, 154.6, 147.5,
137.1, 132.7, 128.6 (2C), 128.4 (2C), 127.2, 126.4, 113.7, 108.9, 52.3, 32.8, 31.8, 27.5, 10.2, 7.1
(2C); HRMS (EI): m/z: calcd for C22H21NO5S: 434.1038 [M+Na]; found: 434.1047.
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7ꢀ(2ꢀCarboxyꢀethyl)ꢀ8ꢀcyclopropylꢀ5ꢀoxoꢀ2ꢀphenylꢀ5Hꢀthiazolo[3,2ꢀa]pyridineꢀ3ꢀcarboxylic
acid methyl ester 14b.
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Prepared according to the procedure for 14a starting from 8 (45 mg, 0.11 mmol), phenyl boronic
acid (41 mg, 0.34 mmol), and purification by column chromatography (CH2Cl2ꢀMeOH 97/3 and
CH2Cl2ꢀMeOHꢀAcOH 95/5/1, from 1/0 to 0/1) to give 14b as a pale yellow solid (32mg, 79%); Rf
= 0.34 (CH2Cl2ꢀMeOHꢀAcOH, 95/5/1); IR (υ cmꢀ1) (neat) 2954, 1734, 1710, 1629, 1545, 1474,
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1429, 1335, 1269, 1171, 1024, 972; H NMR (MeOD:CDCl3), 400 MHz) δ (ppm) 7.56ꢀ7.53 (m,
2H), 7.49ꢀ7.43 (m, 3H), 6.25 (s, 1H), 3.86 (s, 3H), 3.13 (t, 2H, J = 7.8 Hz), 2.66 (t, 2H, J = 7.8 Hz),
1.86 ꢀ1.78 (m, 1H), 1.13ꢀ1.07 (m, 2H), 0.75ꢀ0.69 (m, 2H)); 13C NMR (MeOD:CDCl3, 100
MHz) δ (ppm) 174.5, 161.8, 159.4, 154.3, 147.1, 130.2, 130.1, 129.2 (2C), 128.4 (2C), 128.2,
125.3, 113.4, 109.4, 53.1, 33.2, 27.7, 10.6, 7.7 (2C); HRMS (EI): m/z: calcd for C21H19NO5S:
420.0882 [M+Na]; found: 420.0903.
7ꢀ(2ꢀCarboxyꢀethyl)ꢀ8ꢀcyclopropylꢀ2ꢀmethylꢀ5ꢀoxoꢀ5Hꢀthiazolo[3,2ꢀa]pyridineꢀ3ꢀcarboxylic
acid methyl ester 14c.
Prepared according to the procedure for 14a starting from 8 (38 mg, 0.095 mmol), methyl boronic
acid (17 mg, 0.29 mmol) and purification by column chromatography (CH2Cl2ꢀMeOH 97/3 and
CH2Cl2ꢀMeOHꢀAcOH 95/5/1, from 1/0 to 0/1) to give 14c as a pale yellow solid (25 mg, 79%); Rf
= 0.35 (CH2Cl2ꢀMeOHꢀAcOH, 95/5/1); IR (υ cmꢀ1) (neat) 2949, 1726, 1625, 1541, 1476, 1432,
1337, 1251, 1175, 1061; 1H NMR (CDCl3), 400 MHz) δ (ppm) 6.37 (s, 1H), 3.94 (s, 3H), 3.15ꢀ3.08
(m, 2H), 2.74ꢀ2.67 (m, 2H), 2.37 (s, 3H), 1.81 ꢀ1.72 (m, 1H), 1.11ꢀ1.01 (m, 2H), 0.71ꢀ0.63 (m,
2H)); 13C NMR (CDCl3, 100 MHz) δ (ppm) 175.5, 161.3, 159.0, 153.6, 146.9, 127.2, 127.0, 113.1,
109.8, 53.3, 33.1, 27.4, 11.9, 10.7, 7.9 (2C); HRMS (EI): m/z: calcd for C16H17NO5S: 358.0725
[M+Na]; found: 358.0743.
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7ꢀ(2ꢀCarboxyꢀethyl)ꢀ8ꢀcyclopropylꢀ5ꢀoxoꢀ2ꢀphenylethynylꢀ5Hꢀthiazolo[3,2ꢀa]pyridineꢀ3ꢀ
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carboxylic acid methyl ester 15.
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A mixture of 8 (25 mg, 0.062 mmol), phenylacetylene (20 ꢃL, 0.186 mmol), CuI (1.2 mg, 0.006
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mmol), Pd(Ph3P)2Cl2 (2.1 mg, 0.003 mmol), K2CO3 (42.8 mg, 0.31 mmol) in DMF (1.2 mL) was
°
heated by MWI at 80 C for 10 minutes. The reaction mixture was diluted with CH2Cl2 and
acidified. The organic layer was washed with brine, dried over Na2SO4, filtered and concentrated.
Purification by column chromatography (CH2Cl2ꢀMeOH 97/3 and CH2Cl2ꢀMeOHꢀAcOH 95/5/1,
from 1/0 to 0/1) gave 15 as a yellow solid (23 mg, 80%); Rf = 0.42 (CH2Cl2ꢀMeOHꢀAcOH, 95/5/1);
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IR (υ cmꢀ1) (neat) 2951, 1736, 1704, 1654, 1569, 1474, 1244, 1217, 1163, 1030; H NMR
(MeOD:CDCl3), 400 MHz) δ (ppm) 7.50ꢀ7.48 (m, 2H), 7.41ꢀ7.35 (m, 3H), 6.23 (s, 1H), 3.98 (s,
3H), 3.11 (t, 2H, J = 7.6 Hz), 2.65 (t, 2H, J = 7.6 Hz), 1.82 ꢀ1.75 (m, 1H), 1.13ꢀ1.06 (m, 2H), 0.73ꢀ
0.68 (m, 2H); 13C NMR (MeOD and CDCl3, 100 MHz) δ (ppm) 175.1, 161.2, 159.5, 155.8, 146.9,
133.2, 132.4 (2C), 130.6, 129.2 (2C), 121.5, 114.1, 112.8, 110.3, 101.5, 76.3, 53.9, 33.7, 28.4, 11.2,
8.3 (2C); HRMS (EI): m/z: calcd for C23H19NO5S: 444.0882 [M+Na]; found: 444.0897.
7ꢀ(2ꢀCarboxyꢀethyl)ꢀ8ꢀcyclopropylꢀ5ꢀoxoꢀ2ꢀphenylcarbamoylꢀ5Hꢀthiazolo[3,2ꢀa]pyridineꢀ3ꢀ
carboxylic acid methyl ester 16.
8 (100 mg, 0.25 mmol) was dissolved in THF (10 mL) and cooled to ꢀ78 °C. n-BuLi (0.5 mmol)
was added drop wise and the solution was allowed to warm to ꢀ70 °C and stirred for 10 minutes at
that temperature. PhNCO (82 ꢀL, 0.75 mmol) was added drop wise and the mixture was stirred for
15 minutes at ꢀ70 °C. The reaction was quenched using 2% aq. KHSO4, diluted with CH2Cl2, the
organic layer was washed with water, brine, dried over Na2SO4 and concentrated. Purification by
column chromatography (CH2Cl2ꢀMeOH 97/3 and CH2Cl2ꢀMeOHꢀAcOH 95/5/1, from 1/0 to 0/1)
gave 16 as a yellow solid (71 mg, 64%); Rf = 0.41 (CH2Cl2ꢀMeOHꢀAcOH, 95/5/1); IR (υ cmꢀ1)
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(neat) 3250, 2954, 1740, 1712, 1672, 1635, 1603, 1544, 1472, 1441, 1324, 1246, 1214; H NMR
(MeOD:CDCl3, 400 MHz) δ (ppm) 7.56 (d, 2H, J = 8.4 Hz), 7.34 (t, 2H, J = 8.0 Hz), 7.16 (t, 1H, J
= 7.4 Hz), 6.24 (s, 1H), 3.98 (s, 3H), 3.12 (t, 2H, J = 7.8 Hz), 2.65 (t, 2H, J = 7.8 Hz), 1.83 ꢀ1.75
(m, 1H), 1.14ꢀ1.08 (m, 2H), 0.74ꢀ0.69 (m, 2H); 13C NMR (MeOD:CDCl3, 100 MHz) δ (ppm)
174.4, 162.0, 159.6, 156.8, 155.8, 146.6, 136.8, 129.3 (2C), 125.5, 120.6 (2C), 113.4, 109.8, 53.8,
33.0, 27.8, 10.6, 7.8, 7.5; HRMS (EI): m/z: calcd for C22H20N2O6S: 463.0940 [M+Na]; found:
463.0948.
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Typical procedure for the synthesis of Cꢀ2 substituted BODIPY esters rac-6 and 17aꢀc
The procedure described for 17a is representative for 6 and 17bꢀc
2ꢀBenzylꢀ8ꢀcyclopropylꢀ7ꢀ(2ꢀ(1,3,5,7ꢀtetramethylꢀ4,4ꢀdifluoroꢀ4ꢀboraꢀ3a,4aꢀdiazaꢀsꢀindaceneꢀ
8ꢀyl)ethyl)ꢀ5ꢀoxoꢀ5Hꢀthiazolo[3,2ꢀa]pyridineꢀ3ꢀcarboxylic acid methyl ester 17a.
Oxalyl chloride (0.15 mL, 1.79 mmol) was added drop wise to 14a (368 mg, 0.894 mmol) in
CH2Cl2 (13 mL) at 0 °C and the mixture was allowed to attain rt and stirred for 2 h. The solvent
was evaporated off and the residue dissolved in dry DCE (13 mL). 2,4 Dimethylꢀ1Hꢀpyrrole (0.64
mL, 6.26 mmol) was added and stirred for 40 minutes at rt followed by the addition of
triethylamine (0.87 mL, 6.26 mmol), BF3ꢁEt2O (0.79 mL, 6.26 mmol) and the mixture was heated
by MWI at 140 °C for 90 minutes. The reaction mixture was diluted with CH2Cl2 and acidified.
The organic layer was washed with brine, dried over Na2SO4, filtered and concentrated.
Purification by column chromatography (heptane/EtOAc from 1/0 to 3/2) gave 17a as a reddish
solid (180 mg, 33%); Rf = 0.28 (heptane/EtOAc, 1/1); IR (υ cmꢀ1) (neat) 1726, 1654, 1546, 1507,
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1468, 1305, 1192, 1157, 1074, 1024, 972; H NMR (CDCl3, 400 MHz) δ (ppm) 7.37ꢀ7.27 (m, 5H),
6.35 (s, 1H), 6.06 (s, 2H), 4.03(s, 2H), 4.01 (s, 3H), 3.33ꢀ3.29 (m, 2H), 3.06ꢀ3.01 (m, 2H), 2.53 (s,
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6H), 2.33 (s, 6H), 1.60ꢀ1.52 (m, 1H), 0.97ꢀ0.89 (m, 2H), 0.54ꢀ0.49 (m, 2H)); C NMR (CDCl3,
100 MHz) δ (ppm) 161.4, 158.9, 154.6 (2C), 152.5, 146.9, 144.4, 140.3 (2C), 136.8, 131.4 (2C),
131.3, 129.0 (2C), 128.7 (2C), 127.6, 126.8, 121.9 (2C), 111.9, 108.3, 53.4, 33.0, 32.7, 25.9, 16.4
(2C), 14.6 (2C), 10.6, 8.1 (2C); HRMS (EI): m/z: calcd for C34H34BF2N3O3S: 636.2280 [M+Na];
found: 636.2302.
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8ꢀCyclopropylꢀ7ꢀ(2ꢀ(1,3,5,7ꢀtetramethylꢀ4,4ꢀdifluoroꢀ4ꢀboraꢀ3a,4aꢀdiazaꢀsꢀindaceneꢀ8ꢀ
yl)ethyl)ꢀ5ꢀoxoꢀ2ꢀphenylꢀ5Hꢀthiazolo[3,2ꢀa]pyridineꢀ3ꢀcarboxylic acid methyl ester 17b
Prepared according to the procedure for 17a starting from 14b (28 mg, 0.07 mmol). Purification by
column chromatography (heptane/EtOAc 1/0, to 3/2) gave 17b as a reddish solid (16 mg, 39%); Rf
= 0.33 (heptane/EtOAc, 1/1); IR (υ cmꢀ1) (neat) 2920, 1690, 1652, 1551, 1509, 1471, 1269, 1201,
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1060, 975; H NMR (CDCl3, 400 MHz) δ (ppm) 7.60ꢀ7.57 (m, 2H), 7.47ꢀ7.44 (m, 3H), 6.39 (s,
1H), 6.08 (s, 2H), 3.94 (s, 3H), 3.37ꢀ3.32 (m, 2H), 3.11ꢀ3.06 (m, 2H), 2.54 (s, 6H), 2.36 (s, 6H),
13
1.69ꢀ1.65 (m, 1H), 1.05ꢀ1.02 (m, 2H), 0.65ꢀ0.62 (m, 2H)); C NMR (CDCl3, 100 MHz) δ (ppm)
161.7, 159.0, 154.6 (2C), 152.6, 146.6, 144.3, 140.3 (2C), 131.4, 130.1 (2C), 129.3, 129.3 (2C),
128.5 (2C), 125.5, 121.9 (2C), 111.7, 108.2, 53.5, 33.1, 25.9, 16.5 (2C), 14.6 (2C), 10.7, 8.2 (2C);
HRMS (EI): m/z: calcd for C33H32BF2N3O3S: 622.2123 [M+Na]; found: 622.2136.
8ꢀCyclopropylꢀ7ꢀ(2ꢀ(1,3,5,7ꢀtetramethylꢀ4,4ꢀdifluoroꢀ4ꢀboraꢀ3a,4aꢀdiazaꢀsꢀindaceneꢀ8ꢀ
yl)ethyl)ꢀ2ꢀmethylꢀ5ꢀoxoꢀ5Hꢀthiazolo[3,2ꢀa]pyridineꢀ3ꢀcarboxylic acid methyl ester 17c.
Prepared according to the procedure for 17a starting from 14c (26 mg, 0.08 mmol). Purification by
column chromatography (heptane/EtOAc 1/0 to 2/3) gave 17c as a reddish solid (16 mg, 38%); Rf
= 0.42 (Heptane/EtOAc, 3/7); IR (υ cmꢀ1) (neat) 2924, 1735, 1655, 1553, 1508, 1474, 1311, 1205,
1061, 974; 1H NMR (CDCl3, 400 MHz) δ (ppm) 6.34 (s, 1H), 6.07 (s, 2H), 3.98 (s, 3H), 3.35ꢀ3.31
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(m, 2H), 3.08ꢀ3.04 (m, 2H), 2.53 (s, 6H), 2.39 (s, 3H), 2.34 (s, 6H), 1.64ꢀ1.58 (m, 1H), 1.02ꢀ0.96
(m, 2H), 0.59ꢀ0.55 (m, 2H)); 13C NMR (CDCl3, 100 MHz) δ (ppm) 161.4, 158.7, 154.6 (2C),
152.3, 146.8, 144.4, 140.3 (2C), 131.4, 126.9, 126.8, 121.9 (2C), 111.7, 108.3, 53.3, 33.1, 25.9,
16.5 (2C), 14.6 (2C), 11.9, 10.6, 8.1 (2C); HRMS (EI): m/z: calcd for C28H30BF2N3O3S: 560.1967
[M+Na]; found: 560.1982.
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5ꢀoxoꢀ8ꢀcyclopropylꢀ7ꢀ(2ꢀ(1,3,5,7ꢀtetramethylꢀ4,4ꢀdifluoroꢀ4ꢀboraꢀ3a,4aꢀdiazaꢀsꢀindaceneꢀ8ꢀ
yl)ethyl)ꢀ3,5ꢀdihydroꢀ2Hꢀthiazolo[3,2ꢀa]pyridineꢀ3ꢀcarboxylic acid methyl ester rac-6.
Prepared according to the procedure for 17a starting from 13 (58 mg, 0.18 mmol). Purification by
column chromatography (heptane/EtOAc, from 9/1 to 0/1) gave rac-6 as a brick red solid (39 mg,
41%); Rf = 0.45 (EtOAc); IR (υ cmꢀ1) (neat) 1749, 1644, 1549, 1487, 1407, 1307, 1199, 1157,
1
1075; H NMR (CDCl3, 400 MHz) δ (ppm) 6.25 (s, 2H), 6.07 (s, 1H), 5.58 (dd, 1H, J = 2.4, 8.8
Hz), 3.80 (s, 3H), 3.65 (dd, 1H, J = 8.8, 12.0 Hz), 3.48 (dd, 1H, J = 2.4, 12.0 Hz), 3.29ꢀ3.22 (m,
2H), 2.97ꢀ2.90 (m, 2H), 2.52 (s, 6H), 2.33 (s, 6H), 1.49 ꢀ1.42 (m, 1H), 0.92ꢀ0.80 (m, 2H), 0.57ꢀ0.47
13
(m, 2H). C NMR (CDCl3, 100 MHz) δ (ppm) 168.4, 161.2, 155.8, 154.5, 147.2, 144.3, 140.3,
131.3, 121.8 (2C), 113.2, 111.8, 62.7, 53.2, 32.9, 31.5, 25.3, 16.3 (2C), 14.4 (2C), 10.8, 7.9, 7.5;
HRMS (EI): m/z: calcd for C27H30BF2N3O3S: 548.1967 [M+Na]; found: 548.1981.
Procedure for Hydrolysis
Method A: 1 M aqueous LiOH was added drop wise to a stirred solution of the substrate in THF
(30 mL/mmol) at 0 °C. The solution was then allowed to attain room temperature and was
continuously stirred for 12 h. The mixture was diluted with CH2Cl2 and acidified with 1 M HCl.
The organic layer was dried over Na2SO4, filtered and concentrated. Purification by column
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chromatography (CH2Cl2ꢀMeOH 97/3 and CH2Cl2ꢀMeOHꢀAcOH 90/8/2, from 1/0 to 0/1) gave the
carboxylic acid.
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Method B: LiBr (50.0 equiv.) was added to the substrate in DMF (20 mL/mmol) at rt and the
mixture was heated by MWI at 90/100 °C. The reaction mixture was diluted with water, acidified
and extracted with CH2Cl2. The organic phase was washed with water, brine, dried over Na2SO4,
filtered and concentrated. The crude products were purified by column chromatography (CH2Cl2ꢀ
MeOH 97/3 and CH2Cl2ꢀMeOHꢀAcOH 95/5/1, from 1/0 to 0/1)
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Method C: LiI (50.0 equiv.) was added to the substrate in DMF (20 mL/mmol) at rt and the
mixture heated by MWI for 90 min at 80 °C. The reaction mixture was diluted with water, acidified
and extracted with CH2Cl2. The organic phase was washed with water, brine, dried over Na2SO4,
filtered and concentrated. The crude products were purified by column chromatography (CH2Cl2ꢀ
MeOH 97/3 and CH2Cl2ꢀMeOHꢀAcOH 95/5/1, 1/0 to 0/1)
5ꢀoxoꢀ8ꢀcyclopropylꢀ7ꢀ(2ꢀ(1,3,5,7ꢀtetramethylꢀ4,4ꢀdifluoroꢀ4ꢀboraꢀ3a,4aꢀdiazaꢀsꢀindaceneꢀ8ꢀ
yl)ethyl)ꢀ3,5ꢀdihydroꢀ2Hꢀthiazolo[3,2ꢀa]pyridineꢀ3ꢀcarboxylic acid (rac-18).
By following hydrolysis method A, racꢀ6 (55 mg, 0.105 mmol) gave rac-18 (45 mg, 88%) as brick
red solid; Rf = 0.60 (CH2Cl2ꢀMeOHꢀAcOH, 90/8/2): IR (υ cmꢀ1) (neat) 1720, 1629, 1548, 1492,
1308, 1197, 1157, 1078, 982; 1H NMR (DMSO, 400 MHz) δ (ppm) 6.24 (s, 2H), 6.17 (s, 1H), 5.39
(d, 1H, J = 9.2 Hz), 3.78 (dd, 1H, J = 9.4, 12.2 Hz), 3.49 (d, 1H, J = 12.0 Hz), 3.33ꢀ3.18 (m, 2H),
3.01ꢀ2.82 (m, 2H), 2.41 (s, 6H), 2.35 (s, 6H), 1.60 ꢀ1.52 (m, 1H), 0.84ꢀ0.74 (m, 2H), 0.55ꢀ0.41 (m,
2H). 13C NMR (DMSO, 100 MHz) δ (ppm) 170.1, 160.6, 155.6, 154.1, 148.3, 145.9, 141.5, 131.3,
122.4 (2C), 112.1, 111.5, 62.9, 32.8, 31.7, 25.5, 16.2 (2C), 14.6 (2C), 10.9, 7.9, 7.7. HRMS (EI):
m/z: calcd for C26H28BF2N3O3S: 534.1810 [M+Na]; found: 534.1810.
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2ꢀBenzylꢀ8ꢀcyclopropylꢀ7ꢀ(2ꢀ(1,3,5,7ꢀtetramethylꢀ4,4ꢀdifluoroꢀ4ꢀboraꢀ3a,4aꢀdiazaꢀsꢀindaceneꢀ
8ꢀyl)ethyl)ꢀ5ꢀoxoꢀ5Hꢀthiazolo[3,2ꢀa]pyridineꢀ3ꢀcarboxylic acid 19a.
6
7
8
9
By following hydrolysis method B (MWI at 90 °C for 70 min) 17a (35 mg, 0.057 mmol) gave 19a
(17 mg, 65%) as a reddish solid (yield based on recovered staring material); Rf = 0.36 (CH2Cl2ꢀ
MeOHꢀAcOH, 95/5/1); IR (υ cmꢀ1) (neat) 2922, 1742, 1636, 1610, 1546, 1508, 1473, 1406, 1305,
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1193, 1157, 1079, 974; 1H NMR (DMSO, 400 MHz) δ (ppm) 7.38ꢀ7.24 (m, 5H), 6.33 (s, 1H), 6.26
(s, 2H), 4.09 (s, 2H), 3.37ꢀ3.32 (m, 2H), 3.06ꢀ3.01 (m, 2H), 2.43 (s, 6H), 2.37 (s, 6H), 1.71ꢀ1.65
(m, 1H), 0.90ꢀ0.84 (m, 2H), 0.53ꢀ0.48 (m, 2H); 13C NMR (DMSO, 100 MHz) δ (ppm) 161.7,
158.2, 154.1 (2C), 152.6, 146.9, 145.8, 141.5 (2C), 138.2, 131.2 (2C), 129.3 (2C), 129.0 (2C),
127.6, 122.4 (2C), 111.5, 108.0, 32.8, 32.1, 25.8, 16.2 (2C), 14.6 (2C), 10.8, 8.0 (2C); HRMS (EI):
m/z: calcd for C33H32 BF2N3O3S: 622.2123 [M+Na]; found: 622.2151.
8ꢀCyclopropylꢀ7(2ꢀ(1,3,5,7ꢀtetramethylꢀ4,4ꢀdifluoroꢀ4ꢀboraꢀ3a,4aꢀdiazaꢀsꢀindaceneꢀ8ꢀ
yl)ethyl)ꢀ5ꢀoxoꢀ2ꢀphenylꢀ5Hꢀthiazolo[3,2ꢀa]pyridineꢀ3ꢀcarboxylic acid 19b.
By following hydrolysis method C 17b (27 mg, 0.045 mmol) gave 19b (13 mg, 68%) as a reddish
solid (yield based on recovered starting material); Rf = 0.25 (CH2Cl2ꢀMeOHꢀAcOH, 95/5/1); IR (υ
1
cmꢀ1) (neat) 3300, 2923, 1705, 1636, 1549, 1508, 1466, 1308, 1197, 1157, 1061, 974; H NMR
(MeOD:CDCl3, 400 MHz) δ (ppm) 7.64ꢀ7.61 (m, 2H), 7.44ꢀ7.40 (m, 3H), 6.37 (s, 1H), 6.08 (s,
2H), 3.38ꢀ3.34 (m, 2H), 3.13ꢀ3.08 (m, 2H), 2.49 (s, 6H), 2.35 (s, 6H), 1.72ꢀ1.65 (m, 1H), 1.05ꢀ1.01
13
(m, 2H), 0.65ꢀ0.61 (m, 2H)); C NMR (MeOD:CDCl3, 100 MHz) δ (ppm) 162.6, 159.4, 154.5
(2C), 152.9, 147.3, 144.4, 140.5 (2C), 131.4, 130.0 (2C), 129.2, 129.0 (2C), 128.5 (2C), 126.7,
122.0 (2C), 112.7, 107.8, 33.1, 25.9, 16.2 (2C), 14.2 (2C), 10.6, 8.1 (2C); HRMS (EI): m/z: calcd
for C32H30 BF2N3O3S: 608.1967 [M+Na]; found: 608.1988.
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8ꢀCyclopropylꢀ7ꢀ(2ꢀ(1,3,5,7ꢀtetramethylꢀ4,4ꢀdifluoroꢀ4ꢀboraꢀ3a,4aꢀdiazaꢀsꢀindaceneꢀ8ꢀ
yl)ethyl)ꢀ2ꢀmethylꢀ5ꢀoxoꢀ5Hꢀthiazolo[3,2ꢀa]pyridineꢀ3ꢀcarboxylic acid 19c
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By following hydrolysis method B (MW at 100 °C for 30 min) 17c (15 mg, 0.03 mmol) gave 19c
(7 mg, 55%) as a reddish solid (yield based on recovered starting material); Rf = 0.31 (CH2Cl2ꢀ
MeOHꢀAcOH, 95/5/1); IR (υ cmꢀ1) (neat) 3302, 2924, 1587, 1551, 1508, 1474, 1406, 1309, 1200,
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1155, 1087, 1061; H NMR (CDCl3, 400 MHz) δ (ppm) 6.64 (s, 1H), 6.09 (s, 2H), 3.39ꢀ3.35 (m,
2H), 3.17ꢀ3.13 (m, 2H), 2.85 (s, 3H), 2.54 (s, 6H), 2.35 (s, 6H), 1.72ꢀ1.65 (m, 1H), 1.15ꢀ1.09 (m,
13
2H), 0.66ꢀ0.61 (m, 2H); C NMR (CDCl3, 100 MHz) δ (ppm) 161.1, 159.3, 154.9 (2C), 153.1,
147.4, 143.5, 140.1 (2C), 131.4, 129.5, 122.2 (2C), 116.5, 109.4, 32.8, 25.8, 17.4, 16.6 (2C), 14.5
(2C), 10.7, 8.7 (2C); HRMS (EI): m/z: calcd for C27H28 BF2N3O3S: 546.1810 [M+Na]; found:
546.1822.
Photophysical Measurements:
Absorption spectra were recorded on a UVꢀVISꢀNIR spectrophotometer. The fluorescence spectra
of the reference compound and samples were recorded on a spectrometer equipped with polarizers
at 25 °C. The compounds were dissolved in the solvent and heated to approx. 60 °C for 2 h. The
samples were equilibrated to 25 °C over 1 h. Absorbance spectra were then recorded and compared
to those obtained before heating. Thereafter fluorescence data were collected. The excitation
wavelength (
nm. In order to reduce reꢀabsorption the peak absorbance (@ A,max ) was kept below 0.08. The
fluorescence quantum yield of a sample ( s ) was calculated from:
λ
ex ) was 470 nm and the fluorescence spectrum was collected in the range 480 – 600
λ
Φ
F 1−exp −A (λ
)ln10 n2
(
[
])
s
ref
ex
s
Φ
=Φ
s
ref
F 1−exp −A(λ
)ln10 n2
(
[
])
ref
s
ex
ref
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Here A and F refers to the absorbance at the excitation wavelength, and the integrated fluorescence
spectrum, respectively. The reported quantum yield of the reference substance sodium fluorescein
is 93%.27 The refractive index (n) for the reference and the samples were 1.333 (water) and 1.479
(DMSO). For fluorescence lifetimes, timeꢀresolved fluorescence decays were measured by the
timeꢀcorrelated single photonꢀcounting technique on a spectrometer. For excitation, a pulsed nano
LED centered at 467 nm was used. Data were collected under the magicꢀangle condition. The
fluorescence lifetimes were calculated by using a deconvolution method based on the Levenbergꢀ
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Marquardt algorithm.28 Decay data were fitted to a sum of exponential functions (
and the average fluorescence lifetime calculated from:
aexp(−t /τi
)
)
∑
i
<
τ
>
= a ⋅τ 2
a ⋅τ
∑ ∑
i
i
i
i
i
i
Acknowledgements
We are grateful to the Swedish Research Council (grant no. 621ꢀ2010ꢀ4730) for financial support.
KSK thanks the JC Kempe Foundation and JG the Umeå Centre for Microbial Research for funding
their postdoctoral scholarships.
Abbreviations
Meldrum's acid, 2,2ꢀdimethylꢀ1,3ꢀdioxaneꢀ4,6ꢀdione; MWI, microwave irradiation; PEPPSIꢀ
IPr,[1,3ꢀBis(2,6ꢀDiisopropylphenyl)imidazolꢀ2ꢀylidene](3ꢀchloropyridyl)palladium(II) dichloride;
PEPPSIꢀSIPr, (1,3ꢀBis(2,6ꢀdiisopropylphenyl)imidazolidene) (3ꢀchloropyridyl) palladium(II)
dichloride; TMSI, trimethylsilyl iodide; UPEC, uropathogenic Escherichia coli; UTI, urinary tract
infection.
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Supporting Information.
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1H and 13C NMR spectra of all new compounds, Schemes S1 and S2 comparing old and new
syntheses, Table S1 with examined hydrolysis conditions, Table S2 with LiI halogenolysis of
BODIPY methyl esters, and Figure S1 showing biphasic relaxation. This material is available free
of charge via the Internet at http://pubs.acs.org.
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