Synthesis of VS-105: A novel and potent vitamin D receptor agonist with reduced hypercalcemic effects

Article abstract of DOI:10.1016/j.bmcl.2013.08.076

We have synthesized a novel vitamin D receptor agonist VS-105 ((1R,3R)-5-((E)-2-((3αS,7αS)-1-((R)-1-((S)-3-hydroxy-2, 3-dimethylbutoxy)ethyl)-7α-methyldihydro-1H-inden-4(2H,5H,6H,7H,7αH) -ylidene)ethylidene)-2-methylenecyclohexane-1,3-diol). Preparation o

Full text of DOI:10.1016/j.bmcl.2013.08.076

Bioorganic & Medicinal Chemistry Letters 23 (2013) 5949–5952
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis of VS-105: A novel and potent vitamin D receptor agonist
with reduced hypercalcemic effects q
⇑
Barbara Chen, Megumi Kawai, J. Ruth Wu-Wong
Vidasym, 2201 W. Campbell Park Dr., Suite 13, Chicago, IL 60612, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
We have synthesized a novel vitamin D receptor agonist VS-105 ((1R,3R)-5-((E)-2-((3
((S)-3-hydroxy-2,3-dimethylbutoxy)ethyl)-7a-methyldihydro-1H-inden-4(2H,5H,6H,7H,7aH)-ylidene)
a
S,7
a
S)-1-((R)-1-
Received 10 June 2013
Revised 13 August 2013
Accepted 15 August 2013
Available online 24 August 2013
ethylidene)-2-methylenecyclohexane-1,3-diol). Preparation of a-ring phenylphosphine oxide 11, fol-
lowed by Wittig–Horner coupling of 11 with the protected 25-hydroxy Grundmann’s ketone 22
generated the precursor 12. Deprotection of the TBDMS groups of 12 produced the target compound
VS-105. The biological profiles of VS-105 were evaluated using in vitro assays (VDR receptor binding,
VDR reporter gene and HL-60 differentiation) in comparison to calcitriol (the endogenous hormone) or
paricalcitol. Furthermore, the PTH suppressing potency and hypercalcemic side effects of VS-105 were
evaluated in the 5/6 nephrectomized uremic rats in comparison to paricalcitol. Combining various
changes at 20-epi, 22-oxa, 24-methyl, and 2-methylene yielded VS-105 that not only is highly potent
in inducing functional responses in vitro, but also effectively suppresses PTH in a dose range that does
not affect serum calcium in the 5/6 nephrectomized uremic rats.
Keywords:
Vitamin D analog
Vitamin D receptor
Hypercalcemia
Hyperparathyroidism
Ó 2013 Elsevier Ltd. All rights reserved.
The synthesis of vitamin D3 occurs in the skin, but vitamin D3 is
not active and needs to be converted to 25-hydroxyvitamin D3
(25(OH)D3) and then further hydroxylated (by CYP27B1) to form
the active hormone, calcitriol (1,25(OH)2D3). Calcitriol, the active
bolite of vitamin D, is a secosteroid hormone that, by activating
the vitamin D receptor (VDR), regulates multiple signaling path-
ways in various cells and tissues.1,2 Numerous epidemiological
and bench science studies demonstrate that activated VDR is in-
volved in regulating many genes and functions including PTH,
endothelial function, the cardiovascular, CNS, immune, and renal
systems.3–7
During the past three decades, a majority of the studies in the
VDR field have focused on elucidating its role in mineral homeosta-
sis such as regulation of parathyroid hormone (PTH), intestinal cal-
cium and phosphate absorption and bone metabolism.2
Consequently, it is now well recognized that vitamin D deficiency
results in defective intestinal absorption of calcium and phosphate
and skeletal disorders. Furthermore, calcitriol (the endogenous
VDR modulator, VDRM) and its analogs such as paricalcitol and
doxercalciferol have been developed to treat hyperparathyroidism
secondary to chronic kidney disease,8 osteoporosis9 and
psoriasis.10
Despite encouraging data on VDRM’s benefits for the cardiovas-
cular, immune, and renal systems, currently VDRM is mainly indi-
cated for managing secondary hyperparathyroidism (SHPT) in
CKD,11,12 and to a lesser degree used to treat osteoporosis and pso-
riasis.13,14 The reason for this is due to factors including the narrow
21
22
24
18
20
25
23
H
12
17
15
11
9
13
14
OH
16
8
H
7
6
19
5
2
4
3
10
Abbreviations: Ca, calcium; CKD, chronic kidney disease; NX, nephrectomized;
PTH, parathyroid hormone; Pi, phosphate; VDR, vitamin D receptor; VDRMs, VDR
modulators.
1
OH
HO
q
The results presented in this Letter have not been published previously in whole
or part, except in abstract format.
20-epi-calcitriol
⇑
Corresponding author. Tel.: +1 847 680 6072.
E-mail address: ruth.wuwong@vidasym.com (J.R. Wu-Wong).
Figure 1. The structure of 20-epi-calcitriol.
0960-894X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2013.08.076

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B. Chen et al. / Bioorg. Med. Chem. Lett. 23 (2013) 5949–5952
therapeutic window of current VDRMs in the one to fourfold range
O
as determined by comparing doses required for efficacy versus the
hypercalcemic toxicity. Calcium is important to many body func-
tions and calcium homeostasis is tightly regulated by various
mechanisms including PTH and calcitriol. Hypercalcemia (too
much serum calcium) interferes with numerous physiological
functions. In severe cases hypercalcemia can lead to death. Thus,
hypercalcemia is a serious concern for current VDRMs. Numerous
VDRMs have been made with the intention to curtail their hyper-
calcemic side effect so that they can be developed for indications
beyond their current usages.15 However, very little knowledge is
available regarding the SAR for VDRMs.
A review of the published papers on VDRMs reveals some inter-
esting observations: (1) 20-epi-calcitriol (Fig. 1) is significantly
more potent than calcitriol likely because the 20S configuration
improves the recruiting of specific cofactors to the VDR transcrip-
tional complex.16–19 (2) Transposing the methylene group from C-
10 to C-2 on the A-ring did not significantly alter the activity of the
H
OH
H
OH
HO
VS-105
Figure 2. The structure of VS-105 ((1R,3R)-5-((E)-2-((3
hydroxy-2,3-dimethylbutoxy)ethyl)-7 -methyldihydro-1H-inden-4(2H,5H,6H,7H,
H)-ylidene)ethylidene)-2-methylenecyclohexane-1,3-diol).
aS,7aS)-1-((R)-1-((S)-3-
a
7
a
O
O
O
RO
HO
HO
OH
OH
c
a
b
O
O
TBDMSO
TBDMSO
HO
O
OH
2
OH
3: R = H
D-(-)-quinic acid
4: R = Ac
OH
O
O
HO
AcO
f
e
d
O
TBDMSO
OR
TBDMSO
OH
TBDMSO
7: R = H
8: R = TBDMS
6
5
O
Ph
OH
P
O
Ph
i
h
O
g
22
OTBDMS
TBDMSO
OTBDMS
TBDMSO
TBDMSO
OTBDMS
11
10
9
O
O
H
H
OH
OTBDMS
j
H
H
OH
OTBDMS
HO
TBDMSO
12
VS-105
Figure 3. Synthetic scheme of VS-105. Reagents and conditions: (a) p-TosOH, toluene, TBDMS-Cl;(b) Dess–Martin periodinane, CH2Cl2 (93.2%); Ac2O, pyridine (85.1%); (c) Ph3PCH3Br,
THF, n-BuLi, 0 °C (30.7%); (d) NaBH4, EtOH, 0 °C (50.6%); (e) NaIO4, MeOH, 0 °C (93.7%); 2,6-lutidine, TBDMSOTf, À50 °C (46.6%); (f) LDA, THF, (CH3)3SiCH2CO2CH3, À78 °C (69.6%); (g)
DIBAL-H, toluene, À78 °C (85.9%); (h) n-BuLi, THF, TsCl, 0 °C; Ph2PH, n-Buli, 0 °C; 10% H2O2, 0 °C (78.5%); (i) n-BuLi, THF, À78 °C (37.6%); (j) n-Bu4NF, THF (59.7%).

B. Chen et al. / Bioorg. Med. Chem. Lett. 23 (2013) 5949–5952
5951
O
H
O
OR'
H
H
d
c
b
a
24
(+)-vitamin D2
H
H
H
OR
OSiEt3
OR
16: R = TES
17: R = H
15
13: R = R' = H
14: R = R' = TES
18: R = Ac
O
H
O
O
O
OR
f
OH
H
e
H
O
H
O
H
H
OH
21: R = H
22: R = TBDMS
OAc
20
19
g
Me3SiO
O
HO
O
O
O
24
23
Figure 4. Synthetic scheme of the protected 25-hydroxy Grundmann’s ketone 22. Reagents and conditions: (a) Ozone, CH2Cl2/MeOH, NaBH4, À78 °C (75%); 2,6-lutidine,
TESOTf, THF, À78 °C (80%); (b) (COCl)2, DMSO, CH2Cl2, Et3N, À60 °C (80%); (c) morpholine, toluene, CuCl, O2, CH3CN (38.7%); n-Bu4NF, THF (99%); Ac2O, DMAP, pyridine,
CH2Cl2, 0 °C (93.3%); (d) 24, TESOTf, CH2Cl2, À78 °C, Et3SiH (45.9%); (e) CH3MgBr, THF (98.3%); (f) Dess–Martin periodinane, CH2Cl2 (69.5%); 2,6-lutidine, TBDMSOTf, À50 °C
(63.4%); (g) TMSCl, TEA, CH2Cl2, (65.1%).
Table 1
The synthetic scheme of Vida-105 is outlined in Figure 3.
According to the method described in the literature,30 (À)-quinic
The potency of VS-105 was evaluated in three different in vitro assays in comparison
to calcitriol or paricalcitol
acid was gently refluxed in toluene for 12 h in the presence of
Ligand
IC50/EC50, (nM)
p-toluene sulfonic acid monohydrate and then followed by protec-
tion with tert-butyldimethylsilyl chloride (TBDMS-Cl) to give com-
pound 2. According to the method described in the literature31, 2
was oxidized with Dess–Martin oxidizing reagent to provide 3
(93.2%) and then followed by acylation of the hydroxyl group to
yield 4 (85.1%). Wittig reaction of 4 with methyltriphenylphos-
phine bromide generated 5 (30.7%), which was then followed by
sodium borohydride (NaBH4) reduction to generate compound 6
(50.6%). The resulting alcohol 6 reacted with sodium periodate-
saturated water in methanol at 0 °C to produce the ketone 7 in
93.7% yield. Protection of 7 with tert-butyldimethylsilyl chloride
(TBDMS-Cl) yielded compound 8 (46.6%). Peterson olefination of
VDR receptor binding
VDR reporter gene
HL-60 differentiation
VS-105
Calcitriol
VS-105
Calcitriol
VS-105
Calcitriol
Paricalcitol
38
9.3
<0.1
15
11.8
17.9
12.5
Note: The methods for evaluating the in vitro potency of VDRMs in VDR receptor
binding, VDR reporter gene and HL-60 differentiation assays have been published
previously.32–34
compound.20 (3) A combination of 20S configuration and transpos-
ing the methylene group from C-10 to C-2 on the A-ring signifi-
cantly increases the compound’s activity in inducing HL-60
differentiation and also in promoting intestinal calcium transport
and increase calcium mobilization from the bone.21–23 (4) One sin-
gle change in the calcitriol structure from the carbon atom at the C-
22 position to an oxygen atom reduces VDR binding activity and
also reduces the hypercalcemic potential likely due to different
cofactor recruitment.24–27 (5) Adding an epi-methyl group to the
C-24 position of calcitriol enhances the activity.28
compound
8 with methyl(trimethylsilyl)acetate provided the
methyl ester 9 (69.6%), which on reduction with diisobutylalumi-
num hydride (DIBAL-H) gave 10 (85.9%). The resulting alcohol 10
reacted with diphenylphosphine, and followed by oxidation with
hydrogen peroxide to afford the desired A-ring phenylphosphine
oxide 1137 (78.5%). Wittig–Horner coupling of 11 with the
protected 25-hydroxy Grundmann’s ketone 22 generated 1237
(37.6%), and followed by deprotection of TBDMS-protecting groups
produced the target compound VS-10537 (59.7%).
We raised the question: will combining the changes at 20-epi,
22-oxa, 24-methyl, and 2-methylene affect the potency and the
hypercalcemic potential of a VDRM? We therefore prepared a
The synthesis of protected 25-hydroxy Grundmann’s ketone 22
is described in Figure 4. Compound 13, which was prepared from
Vitamin D2 according to the procedures described by Sardina
et al.29, was protected by triethylsilyl groups in the presence of
2,6-lutidine to give compound 14 (80%). Swern oxidation of 14
with oxalyl chloride and dimethyl sulfoxide (DMSO) afforded 15
in 80% yield. Oxidative cleavage of the aldehyde moiety in 15 with
morpholine and cuprous chloride (CuCl) in the presence of oxygen
compound VS-105 ((1R,3R)-5-((E)-2-((3
hydroxy-2,3-dimethylbutoxy)ethyl)-7 -methyldihydro-1H-inden-
4(2H,5H,6H,7H,7 H)-ylidene)ethylidene)-2-methylenecyclohex-
aS,7aS)-1-((R)-1-((S)-3-
a
a
ane-1,3-diol) as shown in Figure 2 and determined its potency
and hypercalcemic effect using in vitro and in vivo approaches.

5952
B. Chen et al. / Bioorg. Med. Chem. Lett. 23 (2013) 5949–5952
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First
First PTH
suppressing dose
(lg/kg)
hypercalcemic dose
(
lg/kg)
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Paricalcitol
>0.6
>0.08
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0.02
Note: The methods for evaluating the in vivo potency of VDRMs in the 5/6 NX
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to generate the methyl ketone 16 (38.7%). De-protection of 16 with
tetra(n-butyl)ammonium fluoride gave 17, and then followed by
re-protection with acetyl group afforded ketone 18 (93.3%). Reduc-
tive etherification of 18 with trimethylsilyl ether 24 in the
presence of trimethylsilyl-O-triflate and triethylsilane generated
22-Oxa C/D-ring methyl ester 19 (45.9%). Grignard reaction of 19
with methylmagnesium bromide yielded the diol 20 in high yield
(98.3%). Dess–Martin periodinane oxidation of the diol 20 followed
by protection with tert-butyldimethylsilyl group by reacting with
trifluoromethanesulfonate (TBDMSOTf) produced the desired 22-
Oxa C/D-ring ketone 2237 (44% from 20). The trimethylsilyl ether
24 was made by protection of the commercial available methyl
3-hydroxy-(2S)-methyl-n-propanoate 23 with trimethylsilyl
chloride in 65.1% yield.
Since many studies have been published on calcitriol and pari-
calcitol, biological evaluations were done for VS-105 using either
calcitriol or paricalcitol as the ‘bench-mark’ compounds for com-
parison purposes. The in vitro data are summarized in Table 1.
While the binding affinity of VS-105 to VDR is about fourfold less
than that of calcitriol, VS-105 is more potent than calcitriol in
inducing HL-60 differentiation and the expression of VDR reporter
gene.
The effects of VS-105 and paricalcitol on serum calcium and
PTH are compared in the 5/6 nephrectomized uremic rats and
the results are summarized in Table 2. VS-105 is more potent than
paricalcitol in suppressing serum PTH, but significantly less hyper-
calcemic than paricalcitol, suggesting a greatly widened therapeu-
tic window (>50-fold vs 4-fold for paricalcitol).
In summary, by reviewing published papers on existing VDRMs
and combining various changes at 20-epi, 22-oxa, 24-methyl, and
2-methylene, we identified VS-105 that binds to VDR with high
affinity and is highly potent in inducing functional responses
in vitro. More importantly, VS-105 effectively suppresses PTH in
a dose range that does not affect serum calcium in the 5/6 NX ure-
mic rats.
34. Wu-Wong, J. R.; Kawai, M.; Chen, Y. W.; Nakane, M. Br. J. Pharmacol. 2011, 164,
551.
35. Wu-Wong, J. R.; Nakane, M.; Gagne, G. D.; Brooks, K. A.; Noonan, W. T. Int. J.
Endocrinol. 2010, 2010, 1.
36. Wu-Wong, J. R.; Nakane, M.; Chen, Y. W. Life Sci. 2013, 92, 161.
37. Satisfactory spectral characterization of all intermediates was obtained. Data for
11:1H NMR (400 MHz, CDCl3) d 7.76–7.68 (4H, m), 7.54–7.50 (2H, m), 7.48–
7.44 (4H, m), 5.35 (1H, dd, J = 14.2, 6.8 Hz), 4.92 (2H, d, J = 12.7 Hz), 4.34 (2H,
dd, J = 10.8, 4.9 Hz), 3.24–3.03 (2H, m), 2.33 (1H, dt, J = 12.7, 2.9 Hz), 2.08 (1H,
ddd, J = 12.7, 7.8, 4.4 Hz), 2.02 (2H, d, J = 4.4 Hz), 0.86 (18H, s), 0.016 (6H, s),
0.007 (3H, s), À0.004 (3H, s). 12: 1H NMR (400 MHz, CDCl3) d 6.23 (1H, d,
J = 11.2 Hz), 5.81 (1H, d, J = 11.2 Hz), 4.97 (1H, s), 4.92 (1H, s), 4.42 (2H, dd,
J = 8.8, 3.9 Hz), 3.51 (1H, dd, J = 8.8, 3.0 Hz), 3.25–3.19 (2H, m), 2.83 (1H, d,
J = 13.2 Hz), 2.51 (1H, dd, J = 13.2, 5.9 Hz), 2.46 (1H, dd, J = 12.7, 4.4 Hz), 2.33
(1H, dd, J = 12.7, 2.5 Hz), 2.22–2.13 (2H, m), 2.01 (1H, t, J = 9.8 Hz), 1.78–1.10
(10H, m), 1.20 (3H, s), 1.12 (3H, s), 1.06 (3H, d, J = 5.8 Hz), 0.95 (3H, d,
J = 6.8 Hz), 0.90 (9H, s), 0.86 (9H, s), 0.85 (9H, s), 0.55 (3H, s), 0.080 (3H, s),
0.069 (6H, s), 0.065 (3H, s), 0.049 (3H, s), 0.025 (3H, s). 22: 1H NMR (400 MHz,
CDCl3) d 3.49 (1H, dd, J = 8.8, 3.0 Hz), 3.26 (1H, t, J = 8.8 Hz), 3.25–2.18(1H, m),
2.46 (1H, dd, J = 11.2, 7.3 Hz), 2.31–2.18 (3H, m), 1.93–1.82 (1H, m), 2.02–1.94
(1H, m), 1.80–1.69 (3H, m), 1.68–1.62 (1H, m), 1.57–1.52 (3H, m), 1.20 (3H,
s),1.12 (3H, s), 1.07 (3H, d, J = 5.9 Hz), 0.95 (3H, d, J = 6.8 Hz), 0.85 (9H, s), 0.64
(3H, s), 0.069 (6H, s). VS-105: MS: m/z (%) 455 (19) [M+Na]+, 315 (34), 297
(100), 279 (49), 149 (56), 74 (91), 59 (43). HRMS m/z: 455.3059 (Calcd for
Acknowledgments
This study was sponsored by Vidasym, a privately held com-
pany. The authors work as independent contractors for Vidasym
and own Vidasym stock option (<10% of available option shares).
C
27H44O4Na: 455.3137). 1H NMR (400 MHz, CDCl3) d 6.36 (1H, d, J = 11.2 Hz),
5.86 (1H, d, J = 11.2 Hz), 5.10 (2H, d, J = 6.4 Hz), 4.52–4.42 (2H, m), 3.77 (1H, dd,
J = 9.8, 4.4 Hz), 3.70 (1H, br s), 3.32 (1H, dd, J = 9.3, 5.4 Hz), 3.27 (1H, dd, J = 9.8,
5.9 Hz), 2.84 (1H, dd, J = 13.7, 4.9 Hz), 2.81 (1H, dd, J = 10.8, 3.9 Hz), 2.57 (1H,
dd, J = 13.2, 3.9 Hz), 2.35–2.27 (2H, m), 2.14 (1H, d, J = 12.2 Hz), 2.03 (1H, t,
J = 8.3 Hz), 1.81–1.41 (10H, m), 1.24 (3H, s), 1.16 (3H, s), 1.13 (3H, d, J = 5.9 Hz),
1.00 (3H, d, J = 7.3 Hz), 0.57 (3H, s); 13C NMR (400 MHz, CDCl3) d 12.84,
13.87,18.34, 22.52, 23.46, 25.37, 25.92, 29.02, 29.29, 38.21, 40.14, 42.67, 45.64,
45.89, 55.84, 56.84, 70.75, 71.42, 71.87, 72.97, 78.87, 107.81, 115.39, 124.27,
130.63, 143.25, 152.09.
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