Design and development of FGF-23 antagonists: Definition of the pharmacophore and initial structure-activity relationships probed by synthetic analogues

Article abstract of DOI:10.1016/j.bmc.2020.115877

Hereditary hypophosphatemic disorders, TIO, and CKD conditions are believed to be influenced by an excess of Fibroblast Growth Factor-23 (FGF-23) which activates a binary renal FGFRs / α-Klotho complex to regulate homeostatic metabolism of phosphate and vitamin D. Adaptive FGF-23 responses from CKD patients with excess FGF-23 frequently lead to increased mortality from cardiovascular disease. A reversibly binding small molecule therapeutic has yet to emerge from research and development in this area. Current outcomes described in this work highlight efforts related to lead identification and modification using organic synthesis of strategic analogues to probe structure-activity relationships and preliminarily define the pharmacophore of a computationally derived hit obtained from virtual high-throughput screening. Synthetic strategies for the initial hit and analogue preparation, as well as preliminary cellular in vitro assay results highlighting sub micromolar inhibition of the FGF-23 signaling sequence at a concentration well below cytotoxicity are reported herein.

Full text of DOI:10.1016/j.bmc.2020.115877

Bioorg. Med. Chem. 29 (2021) 115877
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Design and development of FGF-23 antagonists: Definition of the
pharmacophore and initial structure-activity relationships probed by
synthetic analogues
,
,
,
Ryan P. Downsa 1, Zhousheng Xiaob 1, Munachi O. Ikedionwua 1, Jacob W. Clevelanda,
Ai Lin China, Abigail E. Caffertya, L. Darryl Quarlesb, Jesse D. Carricka
,
*
a Department of Chemistry, Tennessee Technological University, Cookeville, TN 38505-0001, USA
b Department of Medicine, College of Medicine, University of Tennessee Health Science Center, Memphis, TN 38165, USA
A R T I C L E I N F O
A B S T R A C T
Keywords:
FGF-23
Hereditary hypophosphatemic disorders, TIO, and CKD conditions are believed to be influenced by an excess of
Fibroblast Growth Factor-23 (FGF-23) which activates a binary renal FGFRs / -Klotho complex to regulate
α
Antagonist
Arene
homeostatic metabolism of phosphate and vitamin D. Adaptive FGF-23 responses from CKD patients with excess
FGF-23 frequently lead to increased mortality from cardiovascular disease. A reversibly binding small molecule
therapeutic has yet to emerge from research and development in this area. Current outcomes described in this
work highlight efforts related to lead identification and modification using organic synthesis of strategic ana-
logues to probe structure-activity relationships and preliminarily define the pharmacophore of a computationally
derived hit obtained from virtual high-throughput screening. Synthetic strategies for the initial hit and analogue
preparation, as well as preliminary cellular in vitro assay results highlighting sub micromolar inhibition of the
FGF-23 signaling sequence at a concentration well below cytotoxicity are reported herein.
Oxime
Cross-coupling
1. Introduction
associated with parenteral administration of biologics, developing an
orally available small molecule drug to block the FGF-23 signaling
FGF-23 is a bone-derived signaling biomolecule that activates a
sequence would have several potential advantages, including ease of
administration, shorter half-life, effective dose-titration to more pre-
cisely inhibit FGF-23, and possibly result in greater efficacy and safety.
Virtual high-throughput screening (vHTs) via supercomputing uti-
lizing structure-based molecular dynamics simulations7 employing
ensemble docking strategies8 afforded ZINC13407541 (parent molecule,
named as 1) as an in silico hit for selective FGF-23 antagonism (Fig. 1).
Cellular assays validated 1 as a selective inhibitor of the FGF-23
signaling sequence in an in vitro heterologous cell expression model,
as well as isolated renal tubules ex vivo.9 Preliminary animal model
studies with a murine species that overexpressed FGF-23 resulted in
dose-dependent inhibition, as well as partial reversal of hypo-
phoshatemic effects. With in vitro and preliminary animal model efficacy
of 1 confirmed, medicinal chemistry efforts transitioned to synthetic
route optimization and elaboration towards formulating a lead com-
pound from the original hit while further refining the original scaffold
for greater efficacy and ease of synthetic preparation. Dissemination of
FGFR/α-Klotho binary complex in the kidney to regulate renal meta-
bolism of phosphate and vitamin-D.1 Excess FGF-23 results in rare he-
reditary
hypophosphatemic
disorders,
such
as
X-linked
hypophosphatemia2 (XLH), the autosomal recessive hypophoshatemic
(ARH) bone-softening disorder ricketts,3 and acquired tumor-induced
osteomalacia (TIO).4 Adaptive increases in FGF-23 also maintain phos-
phate and vitamin D homeostasis in chronic kidney disease (CKD) and is
associated with increased cardiovascular (CV) mortality.5 Recently,
antagonizing FGF-23 with a blocking antibody has been successful in
treating hypophosphatemic disorders caused by excess FGF-23. In this
regard, a FGF-23 monoclonal antibody KRN23 (Crysvita®, burosumab)
has been approved for treatment of XLH.6 There is an unmet clinical
therapeutic need for an efficacious small molecule antagonist of FGF-23
that is selective, reversible, and non-biologic in nature as over sup-
pression of FGF-23 has potential toxicities, including hyper-
phosphatemia and vascular calcifications. Because of the disadvantages
* Corresponding author.
E-mail address: jcarrick@tntech.edu (J.D. Carrick).
1
These authors contributed equally to the published work.
https://doi.org/10.1016/j.bmc.2020.115877
Received 29 October 2020; Received in revised form 5 November 2020; Accepted 10 November 2020
Available online 18 November 2020
0968-0896/© 2020 Elsevier Ltd. All rights reserved.

R.P. Downs et al.
Bioorganic & Medicinal Chemistry 29 (2021) 115877
resulted in the production of the necessary advanced aldehyde in-
termediates 6 and 7 for subsequent functional group interconversion.19
Conversion to the oxime 1 was successful under standard conditions
resulting in a 46% yield over three steps from cyclopentanone (2) on
micro scale. During route scouting and validation it was observed that 4
could be directly converted into the oxime 10 in high purity.20 Inter-
mediate 10 was evaluated in parallel Suzuki-Miyaura cross-coupling
reactions towards the production of the functionalized oxime with po-
tassium styrenyltrifluoroborate, but did not afford the desired product in
comparable yield, or purity. The chemistry described in Scheme 1 was
the basis for the production of all requisite functionalized aldehydes,
including the pyridine, benzene, and thiophene oxime analogues of 1
(Scheme 2) 21
Zone 1
Zone 2
HO
N
Zone 3
Fig. 1. Original vHTS hit ZINC13407541 (1) and focus areas for analogue
development.
With an established protocol to install the requisite carbon func-
tionality onto the desired scaffolds, focus turned towards the completion
of the oxime derivatives described in Table 1 for the definition of the
pharmacophore and evaluation of structure-activity relationships pro-
bed by synthetic analogues. The original vHTS hit was divided into three
zones for functional group manipulation towards understanding the
impacts of various structural features of a given antagonist analogue on
in vitro efficacy (Fig. 1). Zone 1 analogues evaluated the significance of
the hydrogen bond donor oxime and related methyl oxime derivative.
Zone 2 analogues studied the impact of saturated ring size through the
common 5- and 6-membered cycloalkanes, in addition to substitution of
phenyl, pyridinyl, and thiophene cores. Whereas, Zone 3 analogues of 1
the synthetic route to the prepared antagonist analogues, definition of
the pharmacophore, probing of structure–activity relationships via
synthetic analogues, and the optimization of in vitro potency of prepared
molecules are reported.
2. Results
2.1. Synthesis
The synthetic construction of analogues as novel FGF-23 antagonists
discovered from vHTS affording 1 was anchored from a common scaffold
derived in several synthetic steps from readily available cycloalkanone
starting materials (Scheme 1). Retrosynthetic analysis of 1 using stan-
dard functional group interconversions of oxime formation10 and metal-
mediated transformations through the Suzuki-Miyaura cross-coupling11
via known chemistry was envisioned.12 The convergency of the route
allowed maximum flexibility of functionality towards pharmacophore
mapping and optimization towards lead identification. Analogues were
proposed to initially focus on variation of functionality to maintain
probed the necessity of extended π-conjugation through the styrenyl, or
direct connect aryl derivatives. The initial optimization analogue scope
of 1 encompassed diverse functionality including conjugated styrenyl
derivatives with aldehydes 4, 5, 11, 12, and 15. Aliphatic analogues (8f,
8g, and 8t) were critical for evaluating the importance of conjugation to
maintenance of more potent biological activity. A vinyl derivative
lacking any aryl ring (8u), as well as direct connect aryl moieties (8l-8s)
were prepared. Aryl moieties with broad substitution patterns (o, m, p,
or poly-) were explored while concomitantly ascertaining the signifi-
cance of resonance- and electron-donating, in addition to electron-
withdrawing functionality. Most oxime end products were afforded as
one major stereoisomer in above 75% average isolated, purified yield.
Structural confirmation of prepared analogues was facilitated via 1H-
and 13C NMR in concert with high-resolution mass spectrometry. The
unoptimized current synthetic route is reproducibly robust and can
support future assay studies without extensive reoptimization.22 With
the realization of a viable synthetic strategy to produce relevant ana-
logues of 1 for structure–activity studies, the focus of the research
shifted to evaluating the in vitro efficacy of the prepared analogues.
conjugation of the extended π-system through the carbonyl and cyclo-
alkene. Evaluation of ring size through the 5- and 6-membered common
rings, in addition to heteroarene constructs was also performed (Scheme
2).
arene and heteroarene constructs were evaluated. Extension of this
strategy towards aryl and Conversion of cyclopentanone to 2-bromocy-
clopentene carbaldehyde using a modified Vilsmeier13 protocol adapted
from Lipton14 afforded the desired synthon for metal-mediated coupling
(4) in 70% yield. This reaction was amenable towards the formation of
the 5-membered bromo-cyclopentene carbaldehyde
4 or the 6-
membered homologue 5.15 Moving forward, treatment of 4 or 5 with
potassium styrenyltrifluoroborate16 using Pd-catalysis via Suzuki-
Miyaura cross-coupling17 conditions optimized in our laboratory18
2.2. In vitro efficacy
To evaluate the potency of the newly synthesized compounds, in vitro
efficacy of the prepared antagonists, as measured by percent inhibition
O
H
O
H
O
using HEK-293 T cells expressing FGFRs/α-Klotho and FGF-23-induced
i
ii
Br
R
ERK reporter activation as the read out, were performed (Fig. 2). Five
distinct groups at 10 M concentration were identified: Group I = 100%
n
n
n
μ
2 n = 1
3 n = 2
4 n = 1
5 n = 2
6 n = 1
7 n = 2
inhibition, Group II = 70–90% inhibition, Group III = 50–70% inhibi-
tion, Group IV = 20–50% inhibition, and Group V < 20% inhibition.
Further structure / activity analysis revealed that the aldehyde precur-
sor to 123 (6a) demonstrated 6-fold lower biological activity (%Max
inhibition 46%) than 1 which underscores the significance of the oxime
moiety to the pharmacophore of 1 in Group IV. The potential for
hydrogen bonding of the oxime versus the methyl oxime 8e which,
displayed <20% inhibition, signifies the importance of this functional
group to the antagonist pharmacophore. Removal of aromatic func-
tionality (8h, 8i, or 8t), or manipulation of the conjugation in 1 with
analogues 8f and 8g proved deleterious to biological activity.
OH
N
H
OH
N
iii
H
Br
R
iii
10
n
8 n = 1
9 n = 2
Scheme 1. Synthesis of compounds 2-10. Reagents and conditions: (i) PBr3,
DMF, rt; (ii) Pd(OAc)2 (5 mol%), RuPhos (10 mol%), RBRn (1.2 equiv), Cs2CO3
(3 equiv), Tol:H2O (4:1), 110 ◦C, 16 h; (iii) NH2OH∙HCl, NaOAc, EtOH /
H2O, rt.
Assessment of substitution of weakly donating alkyl substitutents on
the aryl ring of 8a of core 4, as well as the resonance-donating methoxy-
substituent of 8b highlighted the significance of these structural
2

R.P. Downs et al.
Bioorganic & Medicinal Chemistry 29 (2021) 115877
OH
H
OH
N
N
O
O
i, ii
i, ii
S
S
H
H
H
X
R
X
Br
15
Br
16
R
11 X = C
12 X = N
13 X = C
14 X = N
Scheme 2. Synthesis of compounds 11–14. Reagents and conditions: (i) Pd(OAc)2 (5 mol%), RuPhos (10 mol%), RBRn (1.2 equiv), Cs2CO3 (3 equiv), Tol:H2O (4:1),
110 ◦C, 16 h; (ii) NH2OH∙HCl, NaOAc, EtOH / H2O, rt, 16 h.
Table 1
FGF-23 antagonists prepared based on the structure of the original hit.
amendments to overall potency. Interestingly, manipulation of the cores
from 4 to 5, 11, or 12, while retaining the 4-methylstyrenyl substituent
(9b, 13a, or 14b) as part of the Zone 2 analogues, afforded the most
potent analogues to 1, while demonstrating the relevance of this sub-
stitutent to biological activity. Electrocyclization analogue 8v, afforded
during chromatography of 1, and postulated to potentially be an in vivo
metabolite of 1, produced poor activity results as a constituent of Group
V did not validate the aforementioned hypothesis.24 Subsequent effort
targeted the preparation of analogues which were devoid of the trans-
alkenyl double bond which bridged the core to the aryl substituents.
Excision of the interstitial trans-double bond alleviates two rotatable
bonds,25 modulates lipophilicity slightly, and affords more rapid access
to future functionally group diverse examples vide infra. Compounds 8m
and 8o, direct-connect, aromatic derivatives of 8a and 8b, which
negated the vinyl group, demonstrated lower than half biological ac-
tivity compared to 1 and further validated the relevance of extension of
3

R.P. Downs et al.
Bioorganic & Medicinal Chemistry 29 (2021) 115877
Fig. 2. Comparison of analogues of 1 based on ERK reporter activities at the concentration of 10 µM. Values (mean ± SEM, n = 3–5) with different superscripts (a-e)
are significantly different at P < 0.05.
conjugation, or electron density, as potential influences on increased
activity. Thiophene analogues of 1 were extremely challenging to syn-
thesize and purify. Substantive efforts afforded 16a and 16b which
performed inferiorly to 1. Probing the structural nature of the oxime
with respect to biological activity as part of the Zone 3 analogues,
including the methyl oxime 8a, aldoxime 1 afforded slightly higher
potency. Based on the initial in vitro results presented, eight analogues
were selected from Groups I to IV for IC50 determinations (Table 2).
The IC50 values of prepared FGF-23 antagonist analogues evaluated
μM) in Group I. Cytotoxicity assays revealed that all the test compounds
have no obvious cytotoxicity from 10ꢀ 9 M to 10ꢀ 5 M, which is further
underscored by the fact that IC50 values were dramatically lower than
EC50 values. Only 8n showed markedly stimulated cellular LDH release
at a concentration of 10ꢀ 4 M with 2.30 × 102
μM EC50. The EC50 values
of other compounds with a ranked order are 8a (5.70 × 102
μM), 13a
(6.90 × 102
μ
M), 1 (1.41 × 103
μ
M), 8o (1.91 × 103
μM), and 14b (2.41
× 103
μM), respectively. Future studies will examine the adsorption,
distribution, metabolism, excretion, selectivity and toxicity of these lead
compounds.
ranged from 0.14
μ
M (13a) to 31
M), 8c (0.37
M), 8o (12.3 M) and 6a (31 μ
μ
M (6a) with a ranked order of 13a
M), 14b (0.39 M), 9b (0.52 M), 8n
M), respectively. 8n, 8
(0.14
(2.79
μ
M), 8a (0.20
M), 8 l (10
μ
μ
μ
μ
μ
μ
μ
3. Conclusion
l, and 8o decreased maximum inhibition activity (%Max inhibition 60
~ 70%) in Group II, III, and IV. On the aryl ring of 8a and 8c, a 4-po-
sition electron-donating substituent CH3 for 8a and the resonance-
donating substituent OCH3 for 8c largely increases the efficacy, lead-
ing to 10 ~ 25-fold higher potency for inhibiting FGF-23 activity when
In conclusion, we have described an efficiently convergent and
diversified approach to small-molecule antagonists of the bone-derived
signaling biomolecule FGF-23 from an initial vHTS hit. Structure-
activity relationships were probed from the preparation of expansive
synthetic analogues which have preliminary defined the requisite
pharmacophore of this antagonist class requiring a polar oxime with a
conjugated aryl group with electron-donating substituents being able to
achieve sub 1 µM inhibition in the FGF-23 signaling sequence from in
vitro, cellular IC50 assays. Subsequent lead optimization efforts with
respect to first pass metabolic stability, oral availability, toxicity, and
animal model studies are ongoing in these laboratories and will be re-
ported in due course.
compared to 1 (IC50 5.0 μM) in Group I. The presence of the double bond
in 8c compared to 8o resulted in an order of magnitude increase in
activity for the former, as compared to the latter. In addition, incorpo-
ration of a 6-membered cyclohexenyl ring (9b), aromatic ring (13a) or
heteroaromatic core (14b) on these analogues resulted in 10 ~ 36-fold
higher potency for inhibiting FGF-23 activity as opposed to 1 (IC50 5.0
Table 2
Determination of efficacy (IC50) and cytotoxicity (EC50) for select potent
analogues.
4. Experimental section
Compound
IC50 (µM)
EC50 (µM)
General Considerations: All reagents were purchased from U.S.
chemical suppliers, stored according to published protocols, and used as
received unless indicated otherwise. All experiments were performed in
oven- or flame-dried glassware. Reaction progress was monitored using
thin-layer chromatography on glass-backed silica gel plates and/or 1H
NMR analysis of crude reaction mixtures. RF values for compounds that
resulted in a concentrically observed spot on normal phase silica gel are
reported using the conditions listed. All melting points are reported as
observed and uncorrected. All reported yields listed are for pure
1
5.0
0.14
0.20
0.37
0.39
0.52
2.79
10.0
12.3
1.41 × 103
6.90 × 102
5.70 × 102
–
13a
8a
8c
14b
9b
8n
8l
2.41 × 103
–
2.30 × 102
–
8o
1.91 × 103
4

R.P. Downs et al.
Bioorganic & Medicinal Chemistry 29 (2021) 115877
compounds and corrected for residual solvent or stereoisomeric impu-
calculated for C15H17NO2: 243.1259; found: 243.1265.
1
rities, if applicable, from H NMR spectroscopy unless otherwise indi-
2-[2-(4-Fluoro-phenyl)-vinyl]-cyclopent-1-enecarbaldehyde
oxime (8c): Prepared according to the general procedure discussed
above with 6d (0.30 mmol, 1.00 equiv) and hydroxylamine hydro-
chloride. The crude mixture was concentrated under reduced pressure
and the resulting residue was partitioned between EtOAc:H2O in a
separatory funnel where the organic layer was separated. The aqueous
layer was back extracted with 2 × 10 mL portions of ethyl acetate. The
combined organic layers were washed with 10 mL of a saturated
aqueous NaCl solution, dried over anhydrous sodium sulfate, filtered,
and then concentrated under reduced pressure to afford the title com-
pound: RF = 0.49, 20% MTBE:hexanes; isolated yield 0.067 g, 99%; tan
cated. All 1H and 13C NMR data was acquired from a 500 MHz
multinuclear spectrometer with broad-band N2 cryoprobe. Chemical
shifts are reported using the δ scale and are referenced to the residual
solvent signal: CDCl3 (δ 7.26) and CD3OD (3.31) for 1H NMR and
chloroform (δ 77.16), CD3OD (39.00), and (CD3)2CO (29.84) for 13C
NMR. Splittings are reported as follows: (s) = singlet, (d) = doublet, (t)
= triplet, (dd) = doublet of doublets, (ddd) = doublet of doublet of
doublets, (dt) = doublet of triplets, (br) = broad, (m) = multiplet, and
pent = pentet. Infrared spectral data was acquired from the (form) lis-
ted. High resolution mass spectrometry (HRMS) data was obtained uti-
lizing electron impact ionization (EI) with a magnetic sector (EBE
trisector), double focusing-geometry mass analyzer. The compounds
1
solid; decomposed upon heating for mp analysis; H NMR (500 MHz,
CDCl3): δ 8.40 (s, 1), 7.45–7.40 (m, 2H), 7.14 (d, J = 15.7 Hz, 1H),
7.06–7.01 (m, 2H), 6.58 (d, J = 15.7 Hz, 1H), 2.77 (m, 4H), 1.98 (pent, J
= 7.5 Hz, 2H); 13C NMR (125 MHz, CDCl3): δ 163.9, 161.7, 146.1, 145.6,
133.5, 133.4 (J = 3.0 Hz), 128.3 (J = 8.5 Hz), 121.0 (J = 2.0 Hz), 115.9
(J = 21.8 Hz), 33.8, 32.9, 21.8; IR (ATR-CDCl3): υmax = 3255, 2964, 600,
1507, 1224, 855, 819 cmꢀ 1; HRMS (EI): m/z calculated for C14H14FNO:
231.1059; found: 231.1062.
◦
were stored in the ꢀ 20 C freezer and were tested via in vitro assay.
Recombinant human FGF-23 was purchased from R&D Systems (Min-
neapolis, MN, USA).
General Procedure for Oxime Formation: To an 8 mL reaction vial
equipped with a magnetic stir bar at ambient temperature was charged
the required aldehyde, sodium acetate (1.50 equiv), and hydroxylamine
hydrochloride (1.50 equiv) in ethanol:H2O (3:1) (10 vol) at ambient
temperature. The reaction was continued for 16 h upon which time an
aliquot was removed and analyzed by 1H NMR. Concentration of the
crude reaction mixtures under reduced pressure at ambient temperature
followed by purification on normal phase silica gel using automated
flash-column chromatography with MTBE:hexanes, EtOAc:hexanes, or
MeOH:DCM gradient mobile phases afforded the compounds described
in the listed yields.
2-[2-(4-Trifluoromethyl-phenyl)-vinyl]-cyclopent-1-ene-
carbaldehyde oxime (8d): Prepared according to the general proced-
ure discussed above with 6e (0.86 mmol, 1.00 equiv) and
hydroxylamine hydrochloride. The crude mixture was concentrated
under reduced pressure and the resulting residue was partitioned be-
tween EtOAc:H2O in a separatory funnel where the organic layer was
separated. The aqueous layer was back extracted with 2 × 10 mL por-
tions of ethyl acetate. The combined organic layers were washed with
10 mL of a saturated aqueous NaCl solution, dried over anhydrous so-
dium sulfate, filtered, and then concentrated under reduced pressure to
afford the title compound, RF = 0.47, 20% MTBE:hexanes; isolated yield
2-Styryl-cyclopent-1-enecarbaldehyde oxime (1): Prepared ac-
cording to the general procedure discussed above with 6a26 (0.54 mmol,
1.00 equiv) and hydroxylamine hydrochloride, RF = 0.58, 20% MTBE:
hexanes; purified using automated flash column chromatography using
an MTBE:hexanes gradient mobile phase employing a 5% isocratic hold;
isolated yield 0.195 g, 93%; orange solid; mp = 149.7–152.9 ◦C; 1H
NMR (500 MHz, CDCl3): δ 8.41 (s, 1H), 7.45 (d, J = 7.5 Hz, 2H),
7.36–7.32 (m, 2H), 7.28–7.24 (m, 1H), 7.23 (d, J = 16.0 Hz, 1H), 6.62
1
◦
0.132 g, 52%; gold solid; mp = 179.5–181.2 C; H NMR (500 MHz,
CDCl3): δ 8.41 (s, 1H), 7.60 (d, J = 8.4 Hz, 2H), 7.55 (d, J = 8.4 Hz, 2H),
7.31 (d, J = 16.0 Hz, 1H), 6.63 (d, J = 16.0 Hz, 1H), 2.80–2.72 (m, 4H),
2.00 (pent, J = 7.5 Hz, 2H); 13C NMR (125 MHz, CDCl3): δ 145.9, 144.9,
140.7, 135.3, 130.4, 129.8 (d, J = 31.8 Hz), 126.83, 126.8X (overlaps
with 126.83), 125.8 (d, J = 3.6 Hz), 123.5, 33.7, 30.0, 21.8; IR (ATR-
CDCl3): υmax = 3240, 2965, 2838, 1611, 1457, 1320, 1165, 1119, 1108,
1066, 867, 819 cmꢀ 1; HRMS (EI): m/z calculated for C15H14F3NO:
281.1027; found: 281.1037.
(d, J = 16.0 Hz, 1H), 2.78–2.69 (m, 4H), 1.98 (pent, J = 7.5 Hz, 2H); 13
C
NMR (125 MHz, CDCl3): δ 146.4, 145.8, 137.2, 133.5, 132.2, 128.9,
128.2, 126.8, 121.2, 33.8, 32.9, 21.9; IR (ATR-CDCl3): υmax = 3247,
3032, 2953, 2850, 1649, 1599, 1510, 1006, 948, 939, 753, 693 cmꢀ 1
;
HRMS (EI): m/z calculated for C14H15NO: 213.1154; found: 213.1155.
2-(2-p-Tolyl-vinyl)-cyclopent-1-enecarbaldehyde oxime (8a):
Prepared according to the general procedure discussed above with 6b
(0.30 mmol, 1.00 equiv) and hydroxylamine hydrochloride, RF = 0.51,
20% MTBE:hexanes; purified using automated flash column chroma-
tography using an MTBE:hexanes gradient mobile phase employing a
5% isocratic hold; isolated yield 0.051 g, 75%; off-white solid; mp =
172.9–177.4 ◦C; 1H NMR (500 MHz, CDCl3): δ 8.40 (s, 1H), 7.35 (d, J =
7.5 Hz, 2H), 7.19 (d, J = 16.0 Hz, 1H), 7.15 (d, J = 7.5 Hz, 2H), 6.60 (d,
J = 16.0 Hz, 1H), 2.78–2.68 (m, 4H), 2.35 (s, 3H), 1.97 (pent, J = 7.5 Hz,
2H); 13C NMR (125 MHz, CDCl3): δ 146.4, 145.6, 138.0, 134.4, 132.9,
132.0, 129.5, 126.6, 120.2, 33.7, 32.7, 21.7, 21.2; IR (ATR-CDCl3): υmax
2-Styryl-cyclopent-1-enecarbaldehyde O-methyl-oxime (8e):
Prepared according to the general procedure discussed above with 6a
(0.16 mmol, 1.00 equiv) and methoxyamine hydrochloride, RF = 0.39,
20% MTBE:hexanes; purified using automated flash column chroma-
tography using an MTBE:hexanes gradient mobile phase employing a
5% isocratic hold; isolated yield 0.030 g, 89%; orange solid; mp =
139.0–141.5 ◦C; 1H NMR (500 MHz, CDCl3): δ 8.37 (s, 1H), 7.46–7.42
(m, 2H), 7.36–7.31 (m, 2H), 7.27–7.23 (m, 1H), 7.21 (d, J = 16.0 Hz,
1H), 6.60 (d, J = 16.0 Hz, 1H), 3.94 (s, 3H), 2.74 (t, J = 7.5 Hz, 4H), 1.97
(pent, J = 7.5 Hz, 2H); 13C NMR (125 MHz, CDCl3): δ 145.1, 144.8,
137.4, 133.9, 131.8, 128.9, 128.1, 126.7, 121.4, 62.0, 33.8, 33.0, 21.9;
IR (ATR-CDCl3): υmax = 3031, 2935, 2846, 2816, 1601, 1588, 1495,
1448, 1055, 750, 691 cmꢀ 1; HRMS (EI): m/z calculated for C15H17NO:
227.1310; found: 227.1315.
= 3200, 2955, 2847, 1615, 1583, 1511, 1465, 1006, 940, 801 cmꢀ 1
;
HRMS (EI): m/z calculated for C15H17NO: 227.1310; found: 227.1302.
2-[2-(4-Methoxy-phenyl)-vinyl]-cyclopent-1-enecarbaldehyde
oxime (8b): Prepared according to the general procedure discussed
above with 6c (0.44 mmol, 1.00 equiv) and hydroxylamine hydrochlo-
ride, RF = 0.30, 20% EtOAc:hexanes; purified using automated flash
column chromatography using an MTBE:hexanes gradient mobile phase;
isolated yield 0.074 g, 99%; off-white solid; mp = 151.2–153.0 ◦C; 1H
NMR (500 MHz, CDCl3): δ 8.40 (s, 1H), 7.42–7.38 (m, 2H), 7.11 (d, J =
16.0 Hz, 1H), 6.91–6.86 (m, 2H), 6.58 (d, J = 16.0 Hz, 1H), 3.83 (s, 3H),
2.77–2.68 (m, 4H), 1.97 (pent, J = 7.5 Hz, 2H); 13C NMR (125 MHz,
CDCl3): δ 159.7, 146.5, 14538, 132.4, 131.7, 130.1, 128.1, 119.3, 114.4,
55.5, 33.8, 32.8, 21.8; IR (ATR-CDCl3): υmax = 3260, 3032, 3002, 2841,
1602, 1510, 1248, 1174, 904, 819, 726 cmꢀ 1; HRMS (EI): m/z
2-Phenethyl-cyclopent-1-enecarbaldehyde oxime (8f): Prepared
according to the general procedure discussed above with 6f (0.25 mmol,
1.00 equiv) and hydroxylamine hydrochloride, RF = 0.49, 20% MTBE:
hexanes; purified using automated flash column chromatography using
an MTBE:hexanes gradient mobile phase employing a 5% isocratic hold;
isolated yield 0.020 g, 37%; pale-brown oil; 1H NMR (500 MHz, CDCl3):
δ 7.99 (s, 1), 6.60–6.53 (m, 2H), 6.51–6.43 (m, 3H), 2.02 (t, J = 7.5 Hz,
1H), 1.88–1.79 (m, 4H), 1.76 (t, J = 7.5 Hz, 2H), 1.15 (pent, J = 7.5 Hz,
2H); 13C NMR (125 MHz, CDCl3): δ 149.9, 146.5, 141.5, 130.0, 128.5,
128.4, 126.2, 37.2, 34.7, 32.1, 30.9, 22.0; IR (ATR-CDCl3): υmax = 3204,
3062, 2948, 2921, 1640, 1602, 1496, 1453, 968, 927, 745, 703 cmꢀ 1
;
HRMS (EI): m/z calculated for C14H17NO: 215.1310; found: 215.1305.
5

R.P. Downs et al.
Bioorganic & Medicinal Chemistry 29 (2021) 115877
2-(3-Phenyl-propenyl)-cyclopent-1-enecarbaldehyde
oxime
δ 8.38 (s, 1H), 7.43 (br-s, 1H), 7.20 (d, J = 16.0 Hz, 1H), 6.97–6.92 (m,
2H), 6.72–6.67 (m, 1H), 6.50 (d, J = 16.0 Hz, 1H), 2.77–2.69 (m, 4H),
1.99 (pent, J = 7.5 Hz, 2H); 13C NMR (125 MHz, (CD3)2CO): δ 164.1 (dd,
J = 250.0, 13.0 Hz), 145.8, 143.1, 142.6, 138.0, 129.6 (t, J = 3.0 Hz),
125.4, 110.2 (dd, J = 19.5, 5.5 Hz), 103.1 (t, J = 26.5 Hz), 33.9, 33.7,
23.3; IR (ATR-CDCl3): υmax = 3181, 3078, 2921, 2851, 1612, 1590,
1437, 1122, 980, 951 cmꢀ 1; HRMS (EI): m/z calculated for C14H13F2NO:
249.0965; found: 249.0970.
(8g): Prepared according to the general procedure discussed above with
6g (0.40 mmol, 1.00 equiv) and hydroxylamine hydrochloride: RF
=
0.55, 20% MTBE:hexanes; purified using automated flash column
chromatography using an MTBE:hexanes gradient mobile phase
employing a 5% isocratic hold; isolated yield 0.060 g, 66%; brown
1
liquid; H NMR (500 MHz, CDCl3); major diastereomer: δ 8.25 (s, 1H),
7.33–7.27 (m, 2H), 7.24–7.13 (m, 3H), 6.56 (d, J = 15.5 Hz, 1H), 5.93
(dt, J = 15.5, 7.0 Hz, 1H), 3.50 (d, J = 7.0 Hz, 2H), 2.65 (br-t, J = 7.5 Hz,
2H), 2.59 (br-t, J = 7.5 Hz, 2H), 1.89 (pent, J = 7.5 Hz, 2H); 13C NMR
(125 MHz, CDCl3) major diastereomer: δ 146.2, 145.8, 139.9, 133.7,
131.4, 128.8, 128.7, 126.5, 124.2, 39.8, 34.0, 32.6, 21.7; IR (ATR-
CDCl3): υmax = 3526, 3026, 2845, 1602, 1495, 1452, 994, 957, 931, 748,
698 cmꢀ 1; HRMS (EI): m/z calculated for C15H17NO: 227.1310; found:
227.1306.
2-Phenyl-cyclopent-1-enecarbaldehyde oxime (8l): Prepared ac-
cording to the general procedure discussed above with 6k (0.86 mmol,
1.00 equiv) and hydroxylamine hydrochloride, RF = 0.34, 10% MTBE:
hexanes; purified using automated flash column chromatography using
an MTBE:hexanes gradient mobile phase employing a 5% isocratic hold;
isolated yield 0.118 g, 74%; yellow solid; mp = 105.1–107.1 ◦C; 1H NMR
(500 MHz, CDCl3): δ 8.10 (s, 1H), 7.39–7.35 (m, 2H), 7.32–7.27 (m, 3H),
2-(2-Cyclopentyl-vinyl)-cyclopent-1-enecarbaldehyde
oxime
2.90–2.84 (m, 2H), 2.79–2.74 (m, 2H), 2.02 (pent, J = 7.5 Hz, 2H); 13
C
(8h): Prepared according to the general procedure discussed above with
2-(2-cyclopentyl-vinyl)-cyclopent-1-enecarbaldehyde (0.34 mmol) and
hydroxylamine hydrochloride, RF = 0.66, 20% MTBE:hexanes; purified
using automated flash column chromatography using an MTBE:hexanes
gradient mobile phase employing a 5% isocratic hold; isolated yield
0.040 g, 57%; peach solid; mp = 123.4–128.0 ◦C; 1H NMR (500 MHz,
CDCl3) major oxime diastereomer: δ 8.26 (s, 1H), 6.49 (d, J = 15.5 Hz,
1H), 5.79 (dd, J = 15.5, 8.0 Hz, 1H), 2.67–2.57 (m, 4H), 2.56–2.49 (m,
1H), 1.90 (pent, J = 7.5 Hz, 2H), 1.86–1.78 (m, 2H), 1.71–1.63 (m, 2H),
1.62–1.55 (m, 2H), 1.37–1.28 (m, 2H); 13C NMR (125 MHz, CDCl3)
major oxime diastereomer: δ 146.8, 146.5, 140.6, 130.2, 121.3, 44.2,
34.0, 33.4, 32.6, 24.4, 21.8; IR (ATR-CDCl3): υmax = 3261, 2951, 2868,
1637, 1617, 996, 956, 935 cmꢀ 1; HRMS (EI): m/z calculated for
NMR (125 MHz, CDCl3): δ 148.6, 148.2, 136.7, 131.8, 128.4, 128.0,
127.8, 38.4, 33.0, 22.0; IR (ATR-CDCl3): υmax = 3261, 3055, 3953, 3849,
1601, 1620, 1493, 967, 760, 698 cmꢀ 1; HRMS (EI): m/z calculated for
C
12H13NO: 187.0997; found: 187.1000.
2-p-Tolyl-cyclopent-1-enecarbaldehyde oxime (8m): Prepared
according to the general procedure discussed above with 6l (0.46 mmol,
1.00 equiv) and hydroxylamine hydrochloride, RF = 0.39, 20% MTBE:
hexanes; purified using automated flash column chromatography using
an MTBE:hexanes gradient mobile phase employing a 2.5% isocra1tic
hold; isolated yield 0.065 g, 70%; yellow solid; mp = 157.0–159.5 ◦C; H
NMR (500 MHz, CDCl3): δ 8.20 (s, 1H), 7.34 (s, 4H), 2.96–2.91 (m, 2H),
2.87–2.82 (m, 2H), 2.45 (s, 3H), 2.09 (pent, J = 7.5 Hz, 2H); 13C NMR
(125 MHz, CDCl3): δ 149.2, 148.5, 137.9, 133.8, 130.7, 129.2, 128.1,
38.5, 33.1, 22.1, 21.4; IR (ATR-CDCl3): υmax = 3529, 2961, 2853, 1620,
1513, 1447, 969, 822 cmꢀ 1; HRMS (EI): m/z calculated for C13H15NO:
201.1154; found: 201.1153.
C
13H19NO: 205.1467; found: 205.1459.
2-(2-Cyclohexyl-vinyl)-cyclopent-1-enecarbaldehyde
oxime
(8i): Prepared according to the general procedure discussed above with
6h (0.49 mmol, 1.00 equiv) and hydroxylamine hydrochloride, RF
=
2-(4-tert-Butyl-phenyl)-cyclopent-1-enecarbaldehyde
(8n): Prepared according to the general procedure discussed above with
6m (0.58 mmol, 1.00 equiv) and hydroxylamine hydrochloride, RF
oxime
0.56, 20% EtOAc:hexanes; purified using automated flash column
chromatography using an MTBE:hexanes gradient mobile phase; iso-
lated yield 0.060 g, 56%; cream colored solid; mp = 136.2–137.9 ◦C; 1H
NMR (500 MHz, CDCl3) major diastereomer: δ 8.27 (s, 1H), 6.47 (d, J =
15.5 Hz, 1H), 5.74 (dd, J = 15.5, 7.5 Hz, 1H), 2.63 (t, J = 7.5 Hz, 2H),
2.59 (t, J = 7.5 Hz, 2H), 1.90 (pent, J = 7.5 Hz, 2H), 1.78–1.71 (m, 4H),
1.70–1.63 (m, 1H), 1.35–1.23 (m, 3H), 1.22–1.06 (m, 3H); 13C NMR
(125 MHz, CDCl3) major diastereomer: δ 146.7, 146.1, 141.1, 130.6,
=
0.50, 20% MTBE:hexanes; purified using automated flash column
chromatography using an MTBE:hexanes gradient mobile phase
employing a 5% isocratic hold; isolated yield 0.060 g, 47%; white solid;
mp = 136.0–137.5 ◦C; 1H NMR (500 MHz, CDCl3): δ 8.14 (s, 1H),
7.41–7.37 (m, 2H), 7.25–7.20 (m, 2H), 2.90–2.84 (m, 2H), 2.80–2.73
(m, 2H), 2.01 (pent, J = 7.5 Hz, 2H), 1.35 (s, 9H); 13C NMR (125 MHz,
CDCl3): δ 151.1, 148.8, 148.2, 133.8, 130.9, 127.9, 125.4, 39.4, 34.8,
33.1, 31.4, 22.1; IR (ATR-CDCl3): υmax = 3270, 3036, 2960, 2868, 1617,
1508, 1462, 1442, 969, 834 cmꢀ 1; HRMS (EI): m/z calculated for
120.6, 41.5, 33.9, 33.0, 32.6, 26.2, 26.1, 21.8; IR (ATR-CDCl3): υmax
=
3267, 2994, 2921, 2848, 1637, 1585, 1451, 1003, 955, 933 cmꢀ 1; HRMS
(EI): m/z calculated for C14H21NO: 219.1623; found: 219.1627.
2-[2-(3-Methoxy-phenyl)-vinyl]-cyclopent-1-enecarbaldehyde
oxime (8j): Prepared according to the general procedure discussed
above with 6i (0.35 mmol, 1.00 equiv) and hydroxylamine hydrochlo-
ride, RF = 0.41, 20% MTBE:hexanes; purified using automated flash
column chromatography using an MTBE:hexanes gradient mobile phase
employing a 5% isocratic hold; isolated yield 0.040 g, 51%; off-white
solid; mp = 156.4–158.8 ◦C; 1H NMR (500 MHz, CDCl3): δ 8.41 (s,
1H), 7.28–7.24 (m, 1H), 7.22 (d, J = 16.0 Hz, 1H), 7.07–7.03 (m, 1H),
6.99–6.97 (m, 1H), 6.82 (ddd, J = 8.2, 2.4, 0.8 Hz), 6.58 (d, J = 16.0 Hz,
C
16H21NO: 243.1623; found: 243.1620.
2-(4-Methoxy-phenyl)-cyclopent-1-enecarbaldehyde
oxime
(8o): Prepared according to the general procedure discussed above with
6n (0.76 mmol, 1.00 equiv) and hydroxylamine hydrochloride, RF
=
0.32, 20% MTBE:hexanes; purified using automated flash column
chromatography using an EtOAc:hexanes gradient mobile phase
employing a 2.5% isocratic hold; isolated yield 0.085 g, 51%; yellow
solid; mp = 103.0–106.0 ◦C; 1H NMR (500 MHz, CDCl3): δ 8.12 (s, 1H),
7.24–7.21 (m, 2H), 6.92–6.88 (m, 2H), 3.83 (s, 3H), 2.86–2.82 (m, 2H),
2.78–2.73 (m, 2H), 2.00 (pent, J = 7.5 Hz, 2H); 13C NMR (125 MHz,
CDCl3): δ 159.5, 148.5, 148.1, 130.1, 129.4, 129.2, 114.0, 55.4, 38.4,
30.1, 22.0; IR (ATR-CDCl3): υmax = 3270, 3044, 2838, 1607, 1510, 1462,
1441, 1249, 1178, 1033, 965, 832 cmꢀ 1; HRMS (EI): m/z calculated for
C13H15NO2: 217.1103; found: 217.1098.
1H), 3.85 (s, 3H), 2.78–2.68 (m, 4H), 1.98 (pent, J = 7.5 Hz, 2H); 13
C
NMR (125 MHz, CDCl3): δ 160.1, 146.6, 145.4, 138.7, 133.8, 132.0,
129.9, 121.5, 119.6, 114.0, 111.8, 55.4, 33.8, 32.9, 21.8; IR (ATR-
CDCl3): υmax = 3164, 3002, 2837, 1603, 1575, 1490, 1433, 1261, 1044,
950, 770, 684 cmꢀ 1; HRMS (EI): m/z calculated for C15H17NO2:
234.1259; found: 243.1258.
2-(4-Dimethylamino-phenyl)-cyclopent-1-enecarbaldehyde
oxime (8p): Prepared according to the general procedure discussed
above with 6o (0.35 mmol, 1.00 equiv) and hydroxylamine hydro-
chloride, RF = 0.43, 20% MTBE:hexanes; purified using automated flash
column chromatography using an MTBE:hexanes gradient mobile phase
employing a 2.5% isocratic hold; isolated yield 0.049 g, 60%; beige
solid; mp = 186.0–187.5 ◦C; 1H NMR (500 MHz, CDCl3): δ 8.20 (s, 1H),
7.22–7.18 (m, 2H), 6.72 (br-d, J = 8.5 Hz, 2H), 2.98 (s, 6H), 2.86–2.81
2-[2-(3,5-Difluoro-phenyl)-vinyl]-cyclopent-1-enecarbalde-
hyde oxime (8k): Prepared according to the general procedure dis-
cussed above with 6j (0.30 mmol, 1.00 equiv) and hydroxylamine
hydrochloride, RF = 0.55, 20% MTBE:hexanes; purified using auto-
mated flash column chromatography using an MTBE:hexanes gradient
mobile phase employing a 5% isocratic hold; isolated yield 0.066 g,
88%; pale-pink solid; mp = 171.4–176.1 ◦C; 1H NMR (500 MHz, CDCl3):
6

R.P. Downs et al.
Bioorganic & Medicinal Chemistry 29 (2021) 115877
(m, 2H), 2.77–2.72 (m, 2H), 1.98 (pent, J = 7.5 Hz, 2H); 13C NMR (125
MHz, CDCl3): δ 150.2, 148.8, 148.6, 129.22, 129.2X (overlaps with
129.22), 112.22, 40.6, 38.2, 33.1, 22.0; IR (ATR-CDCl3): υmax = 3195,
2953, 2853, 1610, 1521, 1359, 965, 905, 727 cmꢀ 1; HRMS (EI): m/z
calculated for C14H18N2O: 230.1419; found: 230.1425.
20%; brown oil; 1H NMR (500 MHz, CDCl3) major oxime diastereomer: δ
8.28 (s, 1H), 6.81 (dd, J = 17.0, 10.0 Hz, 1H), 5.29 (d, J = 17.5 Hz, 1H),
5.27 (d, J = 10.0 Hz, 1H), 2.67 (t, J = 7.5 Hz, 2H), 2.62 (t, J = 7.5 Hz,
2H), 1.92 (pent, J = 7.5 Hz, 2H); 13C NMR (125 MHz, CDCl3) major
oxime diastereomer: δ 146.4, 145.6, 133.2, 129.5, 117.5, 33.2, 32.8, 21.6;
IR (ATR-CDCl3): υmax = 3271, 3093, 2925, 2849, 1603, 1009, 992, 937,
909, 733 cmꢀ 1; HRMS (EI): m/z calculated for C8H11NO (M ꢀ H):
136.0757; found: 136.0765.
4-[2-(Hydroxyimino-methyl)-cyclopent-1-enyl]-N-(2-methoxy-
ethyl)-benzamide (8q): Prepared according to the general procedure
discussed above with 4-(2-formyl-cyclopent-1-enyl)-N-(2-methoxy-
ethyl)-benzamide (0.37 mmol) and hydroxylamine hydrochloride, RF =
0.32, 75% EtOAc:hexanes; purified using automated flash column
chromatography using an EtOAc:hexanes gradient mobile phase; iso-
lated yield 0.050 g, 48%; white film; 1H NMR (500 MHz, CDCl3): δ 8.33
(br-s, 1H), 8.07 (s, 1H), 7.80–7.70 (m, 2H), 7.35–7.30 (m, 2H), 6.65 (br-
t, J = 5.0 Hz, 1H), 3.70–3.65 (m, 2H), 3.60–3.56 (m, 2H), 3.41 (s, 3H),
3-Phenyl-6,7-dihydro-5H-[2]pyrindine (8v): Material afforded as
a byproduct to chromatographic purification of 8f above. RF = 0.80,
20% MTBE:hexanes; purified using automated flash column chroma-
tography using an MTBE:hexanes gradient mobile phase employing a
5% isocratic hold; film; 1H NMR (500 MHz, CD3OD): δ 8.42 (s, 1H),
7.88–7.84 (m, 2H), 7.71 (s, 1H), 7.49–7.44 (m, 2H), 7.42–7.40 (m, 1H),
3.05–2.98 (m, 4H), 2.17 (pent, J = 7.5 Hz, 2H); 13C NMR (125 MHz,
CDCl3): δ 157.5, 157.0, 145.5, 140.8, 140.7, 129.8, 129.7, 128.2, 118.9,
33.7, 30.8, 26.2; IR (ATR-CDCl3): υmax = 3201, 3029, 2847, 1606, 1556,
1475, 1448, 1073, 736, 694 cmꢀ 1; HRMS (EI): m/z calculated for
2.89–2.84 (m, 2H), 2.79–2.74 (m, 2H), 2.02 (pent, J = 7.5 Hz, 2H); 13
C
NMR (125 MHz, CDCl3): δ 167.2, 147.5, 147.1, 140.0, 133.7, 133.0,
128.3, 127.2, 71.4, 59.0, 38.8, 38.4, 32.3, 22.1; IR (ATR-CDCl3): υmax
=
3289, 3047, 2926, 2852, 1638, 1609, 1542, 1304, 1117, 966, 853, 732
cmꢀ 1; HRMS (EI): m/z calculated for C16H20N2O3: 288.1474; found:
288.1479.
C
14H13N: 195.1048; found: 195.1048.
2-Styryl-cyclohex-1-enecarbaldehyde oxime (9a): Prepared ac-
2-(4-Methylsulfanyl-phenyl)-cyclopent-1-enecarbaldehyde
oxime (8r): Prepared according to the general procedure discussed
above with 6p (0.73 mmol, 1.00 equiv) and hydroxylamine hydro-
chloride, RF = 0.34, 20% MTBE:hexanes; purified using automated flash
column chromatography using an MTBE:hexanes gradient mobile phase
employing a 10% isocratic hold; isolated yield 0.097 g, 57%; yellow
solid; mp = 141.0–142.5 ◦C; 1H NMR (500 MHz, CDCl3): δ 8.10 (s, 1H),
7.26–7.22 (m, 2H), 7.21–7.17 (m, 2H), 2.87–2.81 (m, 2H), 2.78–2.73
(m, 2H), 2.49 (s, 3H), 2.01 (pent, J = 7.5 Hz, 2H); 13C NMR (125 MHz,
CDCl3): δ 148.3, 148.2, 138.6, 133.4, 131.2, 128.6, 126.4, 38.3, 33.1,
22.1, 15.8; IR (ATR-CDCl3): υmax = 3256, 3002, 2951, 2924, 2850, 1623,
1605, 1591, 965, 818 cmꢀ 1; HRMS (EI): m/z calculated for C13H15NOS:
233.0874; found: 233.0875.
cording to the general procedure discussed above with 7a (0.54 mmol,
1.00 equiv) and hydroxylamine hydrochloride, RF = 0.50, 20% MTBE:
hexanes; purified using automated flash column chromatography using
an MTBE:hexanes gradient mobile phase employing a 2.5% isocratic
hold; isolated yield 0.061 g, 50%; white solid; mp = 142.0–143.0 ◦C; 1H
NMR (500 MHz, CDCl3): δ 8.61 (s, 1H), 7.47–7.43 (m, 2H), 7.39–7.32
(m, 3H), 7.28–7.23 (m, 1H), 6.70 (d, J = 15.9 Hz, 1H), 2.49–2.41 (m,
4H), 1.78–1.65 (m, 4H); 13C NMR (125 MHz, CDCl3): δ 149.1, 139.1,
167.5, 129.6, 129.3, 128.8, 127.9, 126.7, 125.0, 26.9, 25.5, 22.4, 22.1;
IR (ATR-CDCl3): υmax = 3289, 3056, 2931, 2861, 1599, 1582, 1495, 950,
748, 691 cmꢀ 1; HRMS (EI): m/z calculated for C15H17NO: 227.1310;
found: 227.1304.
2-(2-p-Tolyl-vinyl)-cyclohex-1-enecarbaldehyde oxime (9b):
Prepared according to the general procedure discussed above with 7b
(0.35 mmol, 1.00 equiv) and hydroxylamine hydrochloride, RF = 0.49,
20% MTBE:hexanes; purified using automated flash column chroma-
tography using an MTBE:hexanes gradient mobile phase employing a
7.5% isocratic hold; isolated yield 0.059 g, 69%; white solid; mp =
145.5–155.5 ◦C; 1H NMR (500 MHz, CDCl3): δ 8.60 (s, 1H), 7.34 (d, J =
8.0 Hz, 2H), 7.32 (d, J = 16.0 Hz, 1H), 7.15 (d, J = 8.0 Hz, 2H), 6.67 (d,
J = 16.0 Hz, 1H), 2.49–2.40 (br-m, 4H), 2.35 (s, 3H), 1.77–1.65 (m, 4H);
13C NMR (125 MHz, CDCl3): δ 149.3, 139.3, 138.0, 134.7, 129.6, 129.6,
128.8, 126.7, 124.0, 26.9, 25.5, 22.4, 22.1, 21.4; IR (ATR-CDCl3): υmax
2-Benzo[1,3]dioxol-5-yl-cyclopent-1-enecarbaldehyde oxime
(8s): Prepared according to the general procedure discussed above with
6q (0.41 mmol, 1.00 equiv) and hydroxylamine hydrochloride, RF
=
0.34, 20% MTBE:hexanes; purified using automated flash column
chromatography using an MTBE:hexanes gradient mobile phase
employing a 5% isocratic hold; isolated yield 0.062 g, 65%; tan solid;
mp = 139.0–141.5 ◦C; 1H NMR (500 MHz, CDCl3): δ 8.10 (s, 1H),
6.82–6.79 (m, 1H), 6.77–6.74 (m, 2H), 5.98 (s, 2H), 2.84–2.79 (m, 2H),
2.77–2.71 (m, 2H), 2.00 (pent, J = 7.5 Hz, 2H); 13C NMR (125 MHz,
CDCl3): δ 148.5, 148.1, 147.8, 147.5, 130.7, 122.03, 122.0X (overlaps
with 122.03), 108.5, 108.4, 101.3, 38.6, 33.1, 22.0; IR (ATR-CDCl3):
υmax = 3271, 2957, 2895, 2850, 1621, 1605, 1504, 1487, 1440, 1248,
1039, 936 cmꢀ 1; HRMS (EI): m/z calculated for C13H13NO3: 231.0895;
found: 231.0889.
= 3249, 3053, 3017, 2931, 2861, 1611, 1578, 1444, 950, 800 cmꢀ 1
;
HRMS (EI): m/z calculated for C16H19NO: 241.1467; found: 241.1465.
2-(2-p-Tolyl-vinyl)-benzaldehyde oxime (13a): Prepared accord-
ing to the general procedure discussed above with 11a (0.52 mmol, 1.00
equiv) and hydroxylamine hydrochloride, RF = 0.36, 20% MTBE:hex-
anes; purified using automated flash column chromatography using an
MTBE:hexanes gradient mobile phase employing a 10% isocratic hold;
isolated yield 0.050 g, 41%; pale-yellow solid; mp = 125.7–127.3 ◦C; 1H
NMR (500 MHz, CDCl3): δ 8.55 (s, 1H), 7.70 (dd, J = 7.7, 1.3 Hz, 1H0,
7.67 (d, J = 8.0 Hz, 1H), 7.57 (br-s, 1H), 7.49–7.37 (m, 4H), 7.34–7.26
(m, 1H), 7.18 (d, J = 7.7 Hz, 2H), 6.96 (d, J = 16.0 Hz, 1H), 2.38 (s, 3H);
13C NMR (125 MHz, CDCl3): δ 149.5, 138.2, 137.3, 134.5, 132.5, 130.1,
2-(3,3-Dimethyl-butyl)-cyclopent-1-enecarbaldehyde
oxime
(8t): Prepared according to the general procedure discussed above with
2-(3,3-dimethyl-butyl)-cyclopent-1-enecarbaldehyde (0.33 mmol) and
hydroxylamine hydrochloride, RF = 0.55, 20% MTBE:hexanes; purified
using automated flash column chromatography using an MTBE:hexanes
gradient mobile phase employing a 7.5% isocratic hold; isolated yield
0.032 g, 50%; amorphous; 1H NMR (500 MHz, CDCl3): δ 8.10 (s, 1H),
2.54 (br-t, J = 7.5 Hz, 2H), 2.45 (br-t, J = 7.5 Hz, 2H), 2.24–2.18 (m,
2H), 1.86 (pentet, J = 7.5 Hz, 2H), 1.31–1.24 (m, 2H), 0.92 (s, 9H); 13C
NMR (125 MHz, CDCl3): δ 152.2, 146.5, 128.6, 42.7, 37.2, 30.6, 29.3,
24.1, 21.9; IR (ATR-CDCl3): υmax = 3290, 2953, 2866, 1639, 1601, 904,
727, 650 cmꢀ 1; HRMS (EI): m/z calculated for C12H21NO: 195.1623;
found: 195.1620.
129.6, 129.5, 127.6, 126.9, 126.8, 124.6, 21.4; IR (ATR-CDCl3): υmax
=
3307, 3056, 3027, 2920, 1634, 1597, 1515, 1485, 1451, 1302, 961, 804,
753 cmꢀ 1; HRMS (EI): m/z calculated for C16H15NO: (M ꢀ H) 236.1070;
found: 236.1068.
2-[2-(4-Methoxy-phenyl)-vinyl]-benzaldehyde oxime (13b):
Prepared according to the general procedure discussed above with 11b
(0.81 mmol, 1.00 equiv) and hydroxylamine hydrochloride, RF = 0.36,
20% MTBE:hexanes; purified using automated flash column chroma-
tography using an MTBE:hexanes gradient mobile phase; isolated yield
2-Vinyl-cyclopent-1-enecarbaldehyde oxime (8u): Prepared ac-
cording to the general procedure discussed above with 2-vinyl-cyclo-
pent-1-enecarbaldehyde
(0.50
mmol)
and
hydroxylamine
hydrochloride, RF = 0.54, 20% MTBE:hexanes; purified using auto-
mated flash column chromatography using an MTBE:hexanes gradient
mobile phase employing a 7.5% isocratic hold; isolated yield 0.014 g,
1
0.090 g, 65%; pale-yellow solid; mp = 142.3–144.2 ◦C; H NMR (500
MHz, CDCl3): δ 8.52 (s, 1H), 7.67 (dd, (J = 7.8, 1.3 Hz, 1H), 7.59 (d, J =
7

R.P. Downs et al.
Bioorganic & Medicinal Chemistry 29 (2021) 115877
7.8 Hz, 1H), 7.47–7.43 (m, 2H), 7.39–7.35 (m, 1H), 7.34 (d, J = 16.3 Hz,
1H), 7.28–7.26 (m, 1H), 6.95–6.88 (m, 3H), 3.83 (s, 3H); 13C NMR (125
MHz, CDCl3): δ 159.7, 149.6, 137.4, 132.0, 130.0, 129.97, 129.3, 128.1,
127.5, 127.4, 126.7, 123.4, 114.2, 55.4; IR (ATR-CDCl3): υmax = 3193,
2990, 2966, 2912, 2838, 1603, 1511, 1246, 1176, 1030, 980, 959, 824,
811, 761, 546, 517 cmꢀ 1; HRMS (EI): m/z calculated for C16H15NO2:
253.1103; found: 253.1091.
an MTBE:hexanes gradient mobile phase employing a 25% isocratic
hold; isolated yield 0.061 g, 70%; white solid; mp = 103.2–104.7 ◦C; 1H
NMR (500 MHz, CDCl3): δ 8.71 (dd, J = 4.8, 1.8 Hz, 1H), 8.22 (dd, J =
8.0, 1.8 Hz, 1H), 8.16 (br-s, 1H), 7.55–7.51 (m, 2H), 7.50–7.42 (m, 3H),
7.32 (dd, J = 8.0, 4.8 Hz, 1H); 13C NMR (125 MHz, CDCl3): δ 158.5,
150.5, 148.5, 138.6, 134.6, 129.8, 129.0, 128.6, 126.1, 122.5; IR (ATR-
CDCl3): υmax = 3060, 2865, 1564, 1439, 1420, 976, 880, 747, 701 cmꢀ 1
;
4′-Methoxy-biphenyl-2-carbaldehyde oxime (13c): Prepared ac-
cording to the general procedure discussed above with 11c (0.65 mmol,
1.00 equiv) and hydroxylamine hydrochloride, RF = 0.39, 20% MTBE:
hexanes; purified using automated flash column chromatography using
an MTBE:hexanes gradient mobile phase employing a 20% isocratic
hold; isolated yield 0.074 g, 51%; amorphous; 1H NMR (500 MHz,
CDCl3): δ 8.12 (s, 1H), 7.89 (7.3, 1.8 Hz, 1H), 7.42 (dt, J = 7.5, 1.3 Hz,
1H), 7.38–7.31 (m, 2H), 7.26–7.21 (m, 3H), 7.00–6.96 (m, 2H), 3.87 (s,
3H); 13C NMR (125 MHz, CDCl3): δ 159.3, 150.2, 142.1, 132.0, 131.0,
HRMS (EI): m/z calculated for C12H10N2O: 198.0793; found: 198.0793.
2-p-Tolyl-pyridine-3-carbaldehyde oxime (14e): Prepared ac-
cording to the general procedure discussed above with 12e (0.22 mmol,
1.00 equiv) and hydroxylamine hydrochloride, RF = 0.21, 20% MTBE:
hexanes; purified using automated flash column chromatography using
an MTBE:hexanes gradient mobile phase employing a 15% isocratic
hold; isolated yield 0.030 g, 63%; white solid; mp = 203.6–206.2 ◦C; 1H
NMR (500 MHz, CDCl3): δ 8.70 (dd, J = 4.7, 1.7 Hz, 1H), 8.19 (dd, J =
8.0, 1.7 Hz, 1H), 8.17 (s, 1H), 7.45–7.41 (m, 2H), 7.35 (br-s, 1H),
7.30–7.27 (m, 3H), 2.43 (s, 3H); 13C NMR (125 MHz, CDCl3): δ 158.6,
150.6, 148.9, 138.9, 135.8, 134.6, 129.8, 129.3, 125.8, 122.2, 21.5; IR
(ATR-CDCl3): υmax = 3163, 3052, 2990, 2871, 2764, 1615, 1582, 1512,
1424, 977, 881, 827, 773 cmꢀ 1; HRMS (EI): m/z calculated for
130.5, 129.8, 129.75, 128.3, 127.4, 114.0, 55.1; IR (ATR-CDCl3): υmax
=
3299, 3068, 2835, 1610, 1515, 1482, 1442, 1298, 1245, 1178, 955, 834,
763 cmꢀ 1; HRMS (EI): m/z calculated for C14H13NO2: 227.0946; found:
227.0947.
2-Styryl-pyridine-3-carbaldehyde oxime (14a): Prepared accord-
ing to the general procedure discussed above with 12a (0.32 mmol, 1.00
equiv) and hydroxylamine hydrochloride, RF = 0.23, 20% MTBE:hex-
anes; purified using automated flash column chromatography using an
MTBE:hexanes gradient mobile phase employing a 30% isocratic hold;
isolated yield 0.030 g, 42%; white solid; mp = 168.1–171.1 ◦C; 1H NMR
(500 MHz, CDCl3): δ 8.62 (dd, J = 4.7, 1.8 Hz, 1H), 8.54 (s, 1H), 7.98
(dd, J = 8.0, 1.8 Hz, 1H), 7.81 (d, J = 15.6 Hz, 1H), 7.61–7.57 (m, 2H),
7.56 (br-s, 1H), 7.49 (d, J = 15.6 Hz, 1H), 7.40–7.35 (m, 2H), 7.33–7.28
(m, 1H), 7.18 (dd, J = 8.0, 4.7 Hz, 1H); 13C NMR (125 MHz, CDCl3): δ
153.2, 150.6, 147.7, 136.8, 135.9, 135.4, 128.9, 128.8, 127.6, 125.3,
123.3, 122.3; IR (ATR-CDCl3): υmax = 3058, 2879, 2772, 1634, 1578,
1494, 904, 727, 650 cmꢀ 1; HRMS (EI): m/z calculated for C14H12N2O:
(M ꢀ H) 223.0866; found: 223.0872.
C
13H12N2O: 212.0950; found: 212.0951.
2-(4-Methoxy-phenyl)-pyridine-3-carbaldehyde oxime (14f):
Prepared according to the general procedure discussed above with 12f
(0.32 mmol, 1.00 equiv) and hydroxylamine hydrochloride, RF = 0.08,
20% MTBE:hexanes; purified using automated flash column chroma-
tography using an MTBE:hexanes gradient mobile phase employing a
10% isocratic hold; isolated yield 0.061 g, 84%; pale-yellow solid; mp =
208.4–212.1 ◦C; 1H NMR (500 MHz, CDCl3): δ 8.71–8.68 (m, 1H),
8.21–8.16 (br-m, 2H), 7.52–7.47 (m, 2H), 7.30–7.26 (m, 1H), 7.05–6.98
(m, 2H), 3.88 (s, 3H); 13C NMR (125 MHz, CDCl3): δ 160.4, 158.2, 150.6,
149.0, 134.7, 131.3, 131.1, 125.7, 122.0, 114.1, 55.5; IR (ATR-CDCl3):
υmax = 3163, 3068, 2829, 2764, 1608, 1581, 1515, 1423, 1250, 1177,
903, 726 cmꢀ 1; HRMS (EI): m/z calculated for C13H12N2O2: 228.0899;
found: 228.0907.
2-(2-p-Tolyl-vinyl)-pyridine-3-carbaldehyde oxime (14b): Pre-
pared according to the general procedure discussed above with 12b
(0.60 mmol, 1.00 equiv) and hydroxylamine hydrochloride, RF = 0.16,
20% MTBE:hexanes; purified using automated flash column chroma-
tography using an MTBE:hexanes gradient mobile phase employing a
35% isocratic hold; isolated yield 0.101 g, 72%; white solid; mp =
143.9–146.5 ◦C; 1H NMR (500 MHz, CDCl3): δ 8.62 (dd, J = 4.7, 1.8 Hz,
1H), 8.56 (br-s, 1H), 7.99 (dd, J = 7.9, 1.8 Hz, 1H), 7.80 (d, J = 15.9 Hz,
1H), 7.53–7.48 (m, 3H), 7.45 (d, J = 15.9 Hz, 1H), 7.22–7.16 (m, 3H),
2.38 (s, 3H); 13C NMR (125 MHz, CDCl3): δ 153.1, 149.9, 147.3, 139.2,
136.7, 135.9, 133.8, 129.7, 127.6, 125.5, 122.1, 121.5, 21.5; IR (ATR-
CDCl3): υmax = 2986, 2883, 1636, 1581, 1510, 1477, 1407, 1066, 1058,
980, 812, 798 cmꢀ 1; HRMS (EI): m/z calculated for C15H14N2O: (M ꢀ H)
237.1022; found: 237.1029.
3-Styryl-thiophene-2-carbaldehyde oxime (16a): Prepared ac-
cording to the general procedure discussed above with 15a (0.27 mmol,
1.00 equiv) and hydroxylamine hydrochloride, RF = 0.51, 20% MTBE:
hexanes; purified using automated flash column chromatography using
an MTBE:hexanes gradient mobile phase employing a 25% isocratic
hold; isolated yield 0.038 g, 62%; light-brown solid; mp
=
132.9–135.1 ◦C; 1H NMR (500 MHz, CDCl3): δ 8.56 (s, 1H), 7.51 (d, J =
8.1 Hz, 2H), 7.40–7.35 (m, 2H), 7.34–7.28 (m, 2H), 7.26–7.23 (m, 1H),
7.14 (s, 1H), 7.02 (d, J = 16.2 Hz, 1H); 13C NMR (125 MHz, CDCl3): δ
144.1, 140.5, 137.0, 131.5, 130.4, 128.9, 128.3, 127.4, 126.7, 125.7,
120.0; HRMS (EI): m/z calculated for C13H11NOS: 229.0561; found:
229.0555.
3-(4-Methoxy-phenyl)-thiophene-2-carbaldehyde oxime (16b):
Prepared according to the general procedure discussed above with 15b
(0.24 mmol, 1.00 equiv) and hydroxylamine hydrochloride, RF = 0.20,
20% MTBE:hexanes; purified using automated flash column chroma-
tography using an MTBE:hexanes gradient mobile phase employing a
2-[2-(4-Methoxy-phenyl)-vinyl]-pyridine-3-carbaldehyde
oxime (14c): Prepared according to the general procedure discussed
above with 12c (0.21 mmol, 1.00 equiv) and hydroxylamine hydro-
chloride, RF = 0.11, 20% MTBE:hexanes; purified using automated flash
column chromatography using an MTBE:hexanes gradient mobile phase
employing a 15% isocratic hold; isolated yield 0.026 g, 47%; amor-
phous; 1H NMR (500 MHz, CDCl3): δ 8.59 (dd, J = 4.7, 1.7 Hz, 1H), 8.54
(s, 1H), 7.96 (dd, J = 7.9, 1.7 Hz, 1H), 7.77 (d, J = 15.7 Hz, 1H),
7.56–7.52 (m, 2H), 7.44 (br-s, 1H), 7.35 (d, J = 15.7 Hz, 1H), 7.15 (dd, J
= 7.9, 4.7 Hz, 1H), 6.93–6.88 (m, 2H), 3.84 (s, 3H); 13C NMR (125 MHz,
CDCl3): δ 160.3, 153.6, 150.5, 147.6, 135.6, 135.3, 129.5, 129.0, 125.0,
121.9, 121.0, 114.3, 55.5; IR (ATR-CDCl3): υmax = 3162, 3064, 2837,
1
15% isocratic hold; isolated yield 0.022 g, 38%; amorphous; H NMR
(500 MHz, CDCl3): δ 7.70 (br-s, 1H), 7.55 (dd, J = 5.8, 0.7 Hz, 1H),
7.35–7.30 (m, 2H), 7.10 (d, J = 5.0 Hz, 1H), 6.99–6.95 (m, 2H), 3.85 (s,
3H); 13C NMR (125 MHz, CDCl3): δ 159.5, 146.1, 141.3, 131.0, 130.4,
128.53, 128.45, 124.9, 114.2, 55.5; IR (ATR-CDCl3): υmax = 3215, 3100,
3002, 2932, 2841, 1608, 1575, 1528, 1249, 1178, 1031, 833 cmꢀ 1
;
HRMS (EI): m/z calculated for C12H11NO2S: 233.0510; found: 233.0511.
4.1. Minimum inhibitory concentration assays
2771, 1632, 1605, 1575, 1511, 1427, 1253, 1174, 1031, 971, 826 cmꢀ 1
;
HRMS (EI): m/z calculated for C15H14N2O2: 254.1055; found: 254.1052.
2-Phenyl-pyridine-3-carbaldehyde oxime (14d): Prepared ac-
cording to the general procedure discussed above with 12d (0.44 mmol,
1.00 equiv) and hydroxylamine hydrochloride, RF = 0.11, 20% MTBE:
hexanes; purified using automated flash column chromatography using
4.1.1. Cell culture and in vitro functional assays
HEK293T cells were cultured in DMEM containing 10% FBS and 1%
penicillin and streptomycin (P/S). To test the effects of the novel com-
pounds on FGF-23-mediated activation of FGFR1/α-KL complex,
HEK293T cells were transiently transfected with either empty
8

R.P. Downs et al.
Bioorganic & Medicinal Chemistry 29 (2021) 115877
expression vector or full-length human
α
-KL along with the ERK lucif-
previously reported. This material is available free of charge. Supple-
mentary data to this article can be found online at https://doi.
org/10.1016/j.bmc.2020.115877.
erase reporter system12 and Renilla luciferase-null as internal control
plasmid. Transfections were performed by electroporation using Cell
Line Nucleofector Kit® according to the manufacturer’s protocol
(Amaxa, Inc., Gaithersburg, MD). Thirty-six hours after transfection, the
transfected cells were treated with each of the newly synthesized com-
pound (10ꢀ 5 M) or selected compound with a range of 10ꢀ 9 ~ 10ꢀ 4 M in
the presence or absence of 1 nM FGF23 for IC50. After 5 h, the cells were
lysed and luciferase activities measured using a Synergy® H4 Hybrid
Multi-Mode Microplate Reader (Winooski, VT, USA) and Promega®
Dual-Luciferase Reporter Assay System (Madison, WI, USA). The IC50
values of the test compounds were obtained graphically from
concentration-effect curves using Prism 5.0 (GraphPad Software Inc).
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Author contributions
The manuscript was composed from experimental, theoretical, and
written contributions of all authors. All authors have given approval to
the final version of the manuscript.
Funding sources
Financial support for this work was provided by the TN Tech Office
of Research Economic Development and the Department of Chemistry
(J.D.C.), as well as by a grant from the National Institutes of Health, R01-
DK121132 (L.D.Q.). NSF MRI 1531870 is gratefully acknowledged for
the acquisition of TN Tech’s 500 MHz multinuclear NMR spectrometer
with broad-band N2 cryoprobe.
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Declaration of Competing Interest
cross-coupling reaction. The influence of the α, β-propargylic substitution. Org Lett.
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
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Acknowledgement
15 Attempts to adapt this sequence to the 7- or 8-membered ring derivatives were not
successful.
The authors would also like to thank Zachary Z. Gulledge (TN Tech)
for the preparation of 13a and 14b for cytotoxicity assays and Dr. Qiaoli
Liang (UA) for acquisition of HRMS data
16 Boronic acids and pinacoldiborinates were effectively substituted for the potassium
trifluoroborate in several examples. Please see supporting information for further
details.
17 (a) For recent reviews see: Molander GA, Canturk B. Organotrifluoroborates and
monocoordinated palladium complexes as catalystsꢀ a perfect combination for
suzukiꢀ miyaura coupling Angew Chem Int Ed. 2009;48:9240–9261.(b)
Molander GA, Ellis N. Organotrifluoroborates: protected boronic acids that expand
the versatility of the suzuki coupling reaction. Acc Chem Res. 2007;40:275–286.
18 Chin A-L, Carrick JD. Modular approaches to diversified soft lewis basic complexants
through suzuki-miyaura cross-coupling of bromoheteroarenes with
organotrifluoroborates. J Org Chem. 2016;81:1106–1115.
Appendix A. Supplementary material
Synthetic procedures for the construction of select aldehydes requi-
site to analogue formation, in addition to 1H and 13C NMR data for all
analogues not previously disseminated in the primary literature. Auto-
mated flash column chromatograms for select compounds not
9

R.P. Downs et al.
Bioorganic & Medicinal Chemistry 29 (2021) 115877
19 Substitution of the requisite pinacol borinates for the preparation of several
derivatives proceeded favorably under the conditions described. Please see
supporting information.
24 Additional efforts to reproduce this result synthetically were not achieved. Trost, B.
M.; Gutierrez, A. C. Ruthenium catalyzed cycloisomerization-6π-cyclization: a novel
route to pyridines. Org Lett 2007, 9, 1473ꢀ 1476.
20 Aungst Jr RA, Chan C, Funk RL. Total synthesis of the sesquiterpene (+/ꢀ )-illudin C
via and intramolecular nitrile oxide cycloaddition. Org Lett. 2001;3:2611–2613.
21 Additional synthetic and spectroscopic details are delineated in the supporting
information of this paper.
25 (a) Lipinski CA, Lombardo F, Dominy BW, Feeney PJ. Experimental and
computational approaches to estimate solubility and permeability in drug discovery
and development settings. Adv Drug Deliv Rev. 2001;46:3–26.(b) Lipinski CA. Lead
and drug-like compounds. The rule of 5 revolution. Drug Discovery Today,
Technologies. 2004;1:337–341.
22 A scale-up batch afforded over 1.2 g of 1 with an overall yield of 50% over three
steps from 5 in three days.
26 Please see supporting information for aldehyde structure numbers and relevant
spectroscopic and chromatographic data.
23 Compound 6a in the supporting information.
10