Synthesis and conformational analysis of 17α,21-cyclo-22-unsaturated analogues of calcitriol

Article abstract of DOI:10.1021/jo0625195

(Chemical Equation Presented) Six new calcitriol analogues, conformationally restricted at their side chain by the introduction of both a cyclopropane ring at C17-C20 and a double or triple bond at C22, were synthesized using the Wittig-Horner approach to

Full text of DOI:10.1021/jo0625195

VOLUME 72, NUMBER 15
JULY 20, 2007
© Copyright 2007 by the American Chemical Society
Synthesis and Conformational Analysis of
17r,21-Cyclo-22-Unsaturated Analogues of Calcitriol†
Ricardo Riveiros,‡ Antonio Rumbo,§ Luis A. Sarandeses,*,‡ and Antonio Mourin˜o*,§
Departamento de Qu´ımica Fundamental, UniVersidad de A Corun˜a, E-15071 A Corun˜a, Spain, and
Departamento de Qu´ımica Orga´nica y Unidad Asociada al C.S.I.C., UniVersidad de Santiago de
Compostela, E-15782 Santiago de Compostela, Spain
qfsarand@udc.es; qomourin@usc.es
ReceiVed December 8, 2006
Six new calcitriol analogues, conformationally restricted at their side chain by the introduction of both
a cyclopropane ring at C17-C20 and a double or triple bond at C22, were synthesized using the Wittig-
Horner approach to construct the triene system. The six CD-ring and side-chain bearing fragments were
prepared from ketone 14 by a divergent route to generate both series of epimers at C20, followed by
stereoselective cyclopropanation. The (E)-alkenyl side chain was synthesized by means of a Wittig reaction.
The alkynyl side chain was prepared by Corey-Fuchs homologation, followed by alkylation. The (Z)-
alkenyl side chain was prepared from the previous alkyne by partial hydrogenation. The 20-epi analogues
bind more strongly to VDR than the corresponding analogues with the C20 natural stereochemistry.
These results can be reasoned by conformational analysis and hydrophobic interactions with the VDR
ligand-binding domain.
Introduction
in the promotion of cell differentiation, in the inhibition of the
proliferation of various types of malignant cells, and in the
immune response.2 Its best-understood mechanism of action
involves its binding intracellularly to the vitamin D receptor
(VDR), a member of the nuclear receptor superfamily.3
Because the therapeutic utility of calcitriol in the treatment
of cancer and psoriasis is limited by its potent calcemic effects,
Calcitriol [1R,25-dihydroxyvitamin D3, 1R,25-(OH)2-D3, 1a,
Figure 1], the hormonally active form of vitamin D3, is produced
by enzymatic C1-hydroxylation of 25-hydroxyvitamin D3
[25-OH-D3, 1b], which, borne by the vitamin D binding protein
(DBP), is the major circulating form of vitamin D.1 Calcitriol
presents a broad spectrum of biological functions which includes
roles in the regulation of calcium and phosphorus metabolism,
(2) (a) Vitamin D; Feldman, D., Glorieux, F. H., Pike, J. W., Eds.;
Academic Press: San Diego, CA, 1997. (b) Brown, A. J.; Dusso, A.;
Slatopolsky, E. Am. J. Physiol.-Renal Physiol. 1999, 277, F157-F175.
(3) (a) Vitamin D: Molecular Biology, Physiology, and Clinical Ap-
plications; Holick, M. F., Ed.; Humana: Totowa, NJ, 1999. (b) Pru¨fer, K.;
Racz, A.; Lin, G. C.; Barsony, J. J. Biol. Chem. 2000, 275, 41114-41123.
(c) Jurutka, P. W.; Whitfield, G. K.; Hsieh, J. C.; Thompson, P. D.; Haussler,
C. A.; Haussler, M. R. ReV. Endocr. Metab. Disord. 2001, 2, 203-216.
† Dedicated to Professors Joan Bosch and Joaqu´ın Plumet on the occasion of
their 60th birthdays.
‡ Universidad de A Corun˜a.
§ Universidad de Santiago de Compostela.
(1) White, P.; Cooke, N. Trends Endocrinol. Metab. 2000, 11, 320-
327.
10.1021/jo0625195 CCC: $37.00 © 2007 American Chemical Society
Published on Web 03/03/2007
J. Org. Chem. 2007, 72, 5477-5485
5477

Riveiros et al.
able to form hydrogen bonds with a specific region of the VDR
(His305 and His397).
A few years ago, we initiated a program for the development
of calcitriol analogues with selective biological properties by
restricting the mobility and flexibility of the side chain.9 We
prepared calcitriol analogues showing a restricted C25-OH
position and fixed side-chain orientation by introducing: (i) a
double bond or cyclopropane ring at C17-C20, as in 2 and 3
(Figure 1),9a,b (ii) an additional ring at C18-C21 (4),9c or (iii)
multiple unsaturations at the side chain (5).9d These studies
afforded some analogues with significant biological activity,
such as the induction of the transcriptional activity of VDR in
human colon cancer cells9d and also give information about the
bioactive side chain conformation of the natural hormone in
the binding pocket. Following with this program, herein we
describe the synthesis, preliminary biological evaluation, and
conformational analysis of the more tightly restricted analogues,
6, 7, and 8, which feature both a cyclopropane ring at
C17-C20 and a double or triple bond at C22 (Scheme 1).
FIGURE 1. Calcitriol (1a), 25-OH-D3 (1b), and previously described
analogues with restricted C25-OH position or fixed side chain orienta-
tion (2-5).
Results and Discussion
a multitude of vitamin D analogues have been synthesized to
search for derivatives showing higher anti-proliferative activity
and much less calcemic activity than those found in the natural
hormone.4 Most of these vitamin D analogues are modified at
the side chain. With a few exceptions,5 modifications of other
regions of the molecule produce compounds that bind poorly
to VDR, even though they may bind well to the vitamin D
binding protein (DBP).6 Additionally, conformational studies
of analogues with modified side chains,7 together with crystal-
lographic results,8 suggest that activity depends, inter alia, on
the ability to adopt a conformation in which the C25-OH is
Chemical Synthesis.10 The synthesis of compounds 6a, 7a,
and 8a (C20 stereochemistry corresponding to 20R-natural
configuration) and their 20-epimers, 6b, 7b, and 8b (C20
stereochemistry corresponding to 20S-epi configuration), was
envisaged using the convergent Wittig-Horner coupling11
between ketones 9a/b-11a/b, which contain the CD-ring and
side chain fragment, and phosphine oxide 12,12 which provides
the 1R-hydroxylated A-ring (Scheme 1). For the preparation of
ketones 9a/b, 10a/b, and 11a/b we planned a divergent synthetic
strategy starting from known ketone 14.13
In previous work, the C17-C20 cyclopropyl moiety was
introduced in poor yield by direct Simmons-Smith cyclopro-
panation or photochemical methods. Better results were ob-
tained, although under harsh conditions, by dichloropropanation
followed by removal of the chlorine atoms.9a In this case the
construction of the C17-C20 cyclopropyl fragment was intro-
duced by hydroxyl-directed cyclopropanation of an allylic
alcohol containing the C17-C20 double bond under mild
conditions. Starting from ketone 14, stereoselective Horner-
Wadsworth-Emmons reaction with the anion of triethyl phospho-
noacetate afforded the (E)-R,â-unsaturated ester 15 in 97% yield
(Scheme 2) as the only stereoisomer isolated from the reaction
mixture. The synthesis of a-series compounds was followed by
reduction of ester 15 with DIBALH to the (E)-allylic alcohol
16 (97% yield), and further stereoselective hydroxyl-directed
cyclopropanation of 16, by treatment with CH2I2 and Et2Zn.14
The alcohol 13a was obtained in 77% yield as the only isomer
isolated from the reaction mixture. This high stereoselectivity
(4) (a) Bouillon, R.; Okamura, W. H.; Norman, A. W. Endocr. ReV. 1995,
16, 200-257. (b) Carlberg. C.; Mourin˜o, A. Expert Opin. Ther. Patents
2003, 13, 761-772.
(5) A few vitamin D analogues modified at C2, C11, and C12 have shown
VDR binding affinity comparable or higher than 1R,25-(OH)2-D3. For
analogues of this type modified at C2, see: (a) Sicinski, R. R.; Rotkiewicz,
P.; Kolinski, A.; Sicinska, W.; Prahl, J. M. J. Med. Chem. 2002, 45, 3366-
3380. (b) Saito, N.; Suhara, Y.; Kurihara, M.; Fijishima, T.; Honzawa, S.;
Takayanagi, H.; Kozono, T.; Matsumoto, M.; Ohmori, M.; Miyata, N.;
Takayama, H.; Kittaka, A. J. Org. Chem. 2004, 69, 7463-7471. (c)
Glebocka, A.; Sicinski, R.; Plum L. L.; Clagett-Dame, M.; DeLuca, H. F.
J. Med. Chem. 2006, 49, 2909-2920. For analogues modified at C11, see:
(d) Bouillon, R.; Allewaert, K.; van Leeuwen, J. P. T. M.; Tan, B.-K.; Xiang,
D. Z.; De Clercq, P.; Vandewalle, M.; Pols, H. A. P.; Bos, M. P.; van
Baelen, H.; Birkenha¨ger, J. C. J. Biol. Chem. 1992, 267, 3044-3051. For
analogues modified at C12, see: (e) Gonza´lez-Avio´n, X. C.; Mourin˜o, A.
Org. Lett. 2003, 5, 2291-2293. (f) Gonza´lez-Avio´n, X. C.; Mourin˜o, A.;
Rochel, N.; Moras, D. J. Med. Chem. 2006, 49, 1509-1516.
(6) Norman, A. W.; Ishizuka, S.; Okamura, W. H. J. Steroid Biochem.
Mol. Biol. 2001, 76, 49-59.
(7) Conformational analysis on vitamin D analogues: (a) Yamada, S.;
Yamamoto, K.; Masuno, H.; Ohta, M. J. Med. Chem. 1988, 41, 1467-
1475. (b) Okamura, W. H.; Palenzuela, J. A.; Plumet, J.; Midland, M. M.
J. Cell Biochem. 1992, 49, 10-18. (c) Midland, M. M.; Plumet, J.; Okamura,
W. H. Bioorg. Med. Chem. Lett. 1993, 3, 1799-1804. (d) Yamamoto, K.;
Ooizumi, H.; Umesono, K.; Verstuyf, A.; Bouillon, R.; DeLuca, H. F.;
Shinki, T.; Suda, T.; Yamada, S. Bioorg. Med. Chem. Lett. 1999, 9, 1041-
1046. (e) Yamada, S.; Yamamoto, K.; Masuno, H. Curr. Pharm. Design
2000, 6, 733-748. (f) Yamada, S.; Yamamoto, K.; Masuno, H. Steroids
2001, 66, 177-187. (g) Yamada, S.; Shimizu, M.; Yamamoto, K. Med.
Res. ReV. 2003, 23, 89-115. (h) Carlberg, C. J. Cell. Biochem. 2003, 88,
274-281.
(8) (a) Rochel, N.; Wurtz, J. M.; Mitschler, A.; Klaholz, B.; Moras, D.
Mol. Cell 2000, 5, 173-179. (b) Rochel, N.; Tocchini-Valentini, G.; Egea,
P. F.; Juntunen, K.; Garnier, J.-M.; Vihko, P.; Moras, D. Eur. J. Biochem.
2001, 268, 971-979. (c) Verboven, C.; Rabijns, A.; De Maeyer, M.; Van
Baelen, H.; Bouillon, R.; De Ranter, C. Nat. Struct. Biol. 2002, 9, 131-
136.
(9) (a) Mart´ınez-Pe´rez, J. A.; Sarandeses, L.; Granja, J.; Palenzuela, J.
A.; Mourin˜o, A. Tetrahedron Lett. 1998, 39, 4725-4728. (b) Ferna´ndez-
Gacio, A.; Vitale, C.; Mourin˜o, A. J. Org. Chem. 2000, 65, 6978-6983.
(c) Varela, C.; Nilsson, K.; Torneiro, M.; Mourin˜o, A. HelV. Chim. Acta
2002, 85, 3251-3261. (d) Pe´rez-Garc´ıa, X.; Rumbo, A.; Larriba, M. J.;
Ordo´n˜ez, P.; Mun˜oz, A.; Mourin˜o, A. Org. Lett. 2003, 5, 4033-4036.
(10) Steroidal numbering is used for all compounds.
(11) Lythgoe, B. Chem. Soc. ReV. 1981, 9, 449-475.
(12) Mourin˜o, A.; Torneiro, M.; Vitale, C.; Ferna´ndez, S.; Pe´rez-Sestelo,
J.; Anne´, S.; Gregorio, C. Tetrahedron Lett. 1997, 38, 4713-4716.
(13) Ferna´ndez, B.; Mart´ınez-Pe´rez, J. A.; Granja, J. R.; Castedo, L.;
Mourin˜o, A. J. Org. Chem. 1992, 57, 3173-3178.
(14) (a) Furukawa, J.; Kawabata, N.; Nishimura, J. Tetrahedron 1968,
24, 53-58. (b) Denmark, S. E.; Edwards, J. P. J. Org. Chem. 1991, 56,
6974-6981.
5478 J. Org. Chem., Vol. 72, No. 15, 2007

17R,21-Cyclo-22-Unsaturated Analogues of Calcitriol
SCHEME 1. Retrosynthetic Analysis
SCHEME 2. Synthesis of Allylic Alcohols 13a and 13ba
SCHEME 3. Synthesis of Compounds 21a, 24a, and 25aa
a (a) (EtO)2P(O)CH2CO2Et, NaOEt, EtOH, reflux. (b) DIBALH, toluene,
-78 °C. (c) CH2I2, Et2Zn, toluene, -78 °C to rt. (d) t-BuOOH, VO(acac)2,
toluene, -20 °C. (e) LiPPh2, THF, 0 °C, then MeI, rt.
can be explained on the basis of the steric hindrance of the
steroidal â-face.
For the synthesis of compounds with 20-epi configuration
(b series) we considered the same synthetic sequence using the
(Z)-isomer of the allylic alcohol 16. Thus, the isomerization of
the C17-C20 double bond was performed by stereoselective
epoxidation of 16 [t-BuOOH, VO(acac)2, 78%] and subsequent
treatment of the epoxide 17 with LiPPh2 followed by MeI.15
The (Z)-allylic alcohol 18 was converted to 13b by hydroxyl-
directed stereoselective cyclopropanation with CH2I2 and
Et2Zn in 93% yield. Remarkably, both the epoxidation and the
cyclopropanation occur, with complete stereoselectivity, as in
the case of the previous compound, 13a.
a (a) DMSO, (COCl)2, CH2Cl2, then Et3N, rt. (b) Ph3P+CH2CH2C(Me)2OH,
Br- (20), MeLi, THF, -20 °C. (c) MOMCl, i-Pr2NEt, CH2Cl2, 0 °C. (d)
CBr4, Ph3P, Zn, py, CH2Cl2. (e) n-BuLi, THF, -78 °C. (f) n-BuLi, THF,
-78 °C, then BF3•OEt2, 1,2-isobutylene oxide, -78 °C to rt. (g) H2, Lindlar,
hexanes, rt.
the Salmond procedure,16 reaction of 19a with the ylide
generated from phosphonium salt 2017 (Scheme 3) by treatment
with MeLi, yielded a mixture of alkenols 22(E):22(Z) in 7.5:1
The synthesis of the CD-ring and side chain bearing fragments
with C20-natural stereochemistry (21a, 24a, and 25a) from
cyclopropylcarbinol 13a is depicted in Scheme 3. Swern
oxidation of 13a gave aldehyde 19a in 91% yield. Following
(16) Salmond, W. G.; Barta, M. A.; Havens, J. L. J. Org. Chem. 1978,
43, 790-792.
(15) (a) Vedejs, E.; Fuchs, P. L. J. Am. Chem. Soc. 1971, 93, 4070-
4072. (b) Vedejs, E.; Fuchs, P. L. J. Am. Chem. Soc. 1973, 95, 822-825.
(17) Fall, Y.; Vitale, C.; Mourin˜o, A. Tetrahedron Lett. 2000, 41, 7337-
7340.
J. Org. Chem, Vol. 72, No. 15, 2007 5479

Riveiros et al.
SCHEME 4. Synthesis of 20-epi Compounds 21b, 24b, and
SCHEME 5. Synthesis of Vitamin D3 Analogues 6a, 7a, and
8aa
25ba
a (a) TBAF, THF, reflux. (b) PDC, PPTS cat., CH2Cl2, rt. (c) 12, n-BuLi,
THF, -78 °C. (d) TBAF, THF, rt, then AG 50W-X4, MeOH, rt.
a (a) DMSO, (COCl)2, CH2Cl2, then Et3N, rt. (b) Ph3P+CH2CH2C(Me)2OH,
Br- (20), MeLi, THF, -20 °C. (c) MOMCl, i-Pr2NEt, CH2Cl2, 0 °C. (d)
CBr4, Ph3P, Zn, py, CH2Cl2. (e) n-BuLi, THF, -78 °C. (f) n-BuLi, THF,
-78 °C, then BF3•OEt2, 1,2-isobutylene oxide, -78 °C to rt. (g) H2, Lindlar,
hexanes, rt.
isomers in 8:1 ratio (E:Z). This mixture was used to prepare
analogue 6b, which was separated from the corresponding
isomer by HPLC. The Corey-Fuchs homologation of 19b and
acetylide alkylation occurred in 82% yield (three steps), and
the 25-MOM protected 20-epi compounds 24b and 25b were
obtained in good yields (90 and 83%, respectively, from 23b).
The synthesis of calcitriol analogues 6a/b, 7a/b, and 8a/b
was accomplished from their precursors 21a/b, 24a/b, and
25a/b, respectively, following a common five-step synthetic
sequence consisting in (i) deprotection of C8 hydroxyl group
by treatment with TBAF, (ii) further oxidation of the resulting
C8 alcohol with PDC, and (iii) Wittig-Horner reaction with
the anion derived from the phosphine oxide 12. Finally, the
resulting protected calcitriol analogues were deprotected by (iv)
treatment with TBAF to remove the silyl protecting groups at
C1 and C3, and (v) treatment with AG 50W-X4 resin to further
deprotect the C25 hydroxyl group (Schemes 5 and 6). After
this synthetic sequence, vitamin D analogues 6a, 7a, and 8a
were synthesized in 10-13 steps and 20-32% overall yield
from 14 (Scheme 5), and the 20-epimers 6b, 7b, and 8b in
12-15 steps and 25% overall yield from 14 (Scheme 6).
Biological Evaluation. The biological evaluation of the
vitamin D3 analogues 6a/b, 7a/b, and 8a/b includes: (a) binding
affinity for the calf thymus VDR,19 (b) binding affinity for the
human vitamin D binding protein (hDBP),20 and (c) cell-
ratio. Pure 22(E)-stereoisomer was obtained after purification
by HPLC. The 22(E) stereochemistry can be explained on the
basis of an internal Schlosser “trans-selective Wittig” mecha-
nism.16 Finally, protection of the C25 hydroxyl group as an
MOM ether, afforded the desired compound 21a in 75% yield
(two steps).
The synthesis of both the alkynyl and the (Z)-alkenyl side
chains, necessary for the preparation of 7 and 8, started with
Corey-Fuchs homologation18 of 19a to form the alkyne 22a
in 80% yield. Subsequent alkylation of the acetylide, generated
from 22a with 1,2-isobutylene oxide in the presence of a Lewis
acid such as BF3‚OEt2, afforded the alkynol 23a in good yield
(70%, three steps from 19a). Finally, protection of the C25
hydroxyl group in 23a as MOM ether, produced compound 24a
in 80% yield. Partial hydrogenation of 23a with Lindlar catalyst
followed by protection of the hydroxyl group as MOM ether,
gave 25a in 80% yield (two steps).
The 20-epi precursors, 21b, 24b, and 25b, were prepared from
13b in a similar synthetic sequence to that of their C20 epimers,
as depicted in Scheme 4. In this case, the Wittig reaction under
Salmond conditions16 afforded alkene 21b as a mixture of
(18) (a) Corey, E. J.; Fuchs, P. L. Tetrahedron Lett. 1972, 3769-3772.
(b) Mascaren˜as, J. L.; Sarandeses, L. A.; Castedo, L.; Mourin˜o, A.
Tetrahedron 1991, 47, 3485-3498.
(19) (a) Procsal, D. A.; Okamura, W. H.; Norman, A. W. J. Biol. Chem.
1975, 250, 8382-8388. (b) Wecksler, W. R.; Norman, A. W. Methods
Enzymol. 1980, 67, 488-494.
5480 J. Org. Chem., Vol. 72, No. 15, 2007

17R,21-Cyclo-22-Unsaturated Analogues of Calcitriol
TABLE 1. Biological Activities of Compounds 6, 7, and 8a
cell
SCHEME 6. Synthesis of 20-epi Vitamin D3 Analogues 6b,
7b, and 8ba
binding
differentiation
compound
VDR (calf thymus)
DBP (human)
HL-60
1
100
4
17
116
75
100
14
0
2
2
100
1.5
10
3
50
0.6
50
6a
7a
8a
6b
7b
8b
0.8
176
0
19
a Activities of the vitamin D3 analogues are presented as relative values
with respect to 1R,25-(OH)2-D3 (1, 100%).
DBP. For VDR binding, the best value was exhibited by the
22(Z) compounds 8b (176%) and 8a (116%), followed by
the 20-epi-22(E) compound 6b (75%) and 7a (17%). None of
the others show significant binding to VDR. The side chain
olefinic compounds 6b and 8b with the 20S (20-epi) configu-
ration at C20, which bind well to VDR, also induce a significant
cell-differentiating activity (50%). The other compounds
were e10% active compared to that of 1R,25-(OH)2-D3
(100% activity).
Conformational Analysis. To gain insight into the confor-
mational-function relationships of the new vitamin D3 analogues,
we explored the conformational profile of their side chains. The
low-energy side chain conformations are represented in the form
of dot maps which reflect the sites most accessible by the tertiary
hydroxyl groups. Figure 2 shows the superimposition of
structures of 25-OH-D3 and 1R,25-(OH)2-D3 bound to DBP8c
and VDR-LBD,8a respectively, maintaining the corresponding
CD ring systems as closely as possible. The dot maps corre-
sponding to conformational minima were superimposed atop
of the CD hydrindane moiety.
None of the side chains reach the C25-OH group of 25-OH-
D3 bound to DBP explaining the negligible or low binding of
the new compounds to DBP. The side chains of 6a, 7a, and 7b
are also too conformationally restricted to reach the C25-OH
group of 1R,25-(OH)2-D3 bound to VDR-LBD. However 6b,
8a, and 8b can place their side chain hydroxyl groups suitably
for VDR binding. The dot maps of 8a (20R natural stereochem-
istry) indicate that the C25-OH group is located toward the right
a (a) TBAF, THF, reflux. (b) PDC, PPTS cat., CH2Cl2, rt. (c) 12, n-BuLi,
THF, -78 °C. (d) TBAF, THF, rt, then AG 50W-X4, MeOH, rt.
differentiating activity in vitro on HL-60 human leukaemia cell
lines.21 Results are given in Table 1. None of the new
compounds showed significant affinity for DBP in comparison
with the natural hormone. The most active were 8b (19%) and
6a (14%). The other compounds do not bind significantly to
FIGURE 2. Structures of DBP-bound 25-OH-D3 (gray) and VDR-LBD-bound 1R,25-(OH)2-D3 (green), with their CD systems superimposed.
The dot maps are superimposed atop the CD hydrindane moiety and identify an occupancy volume for the location of the side chain hydroxyl group
of the new vitamin D3 analogues 6, 7, and 8.
J. Org. Chem, Vol. 72, No. 15, 2007 5481

Riveiros et al.
(5% EtOAc/hexanes) to afford 15 [3.6 g, 97%, Rf ) 0.4 (5% EtOAc/
hexanes), colorless oil]. 1H NMR δ 5.47 (t, J ) 2.4 Hz, 1 H), 4.13
(m, 3 H), 2.81 (m, 2 H), 1.26 (t, J ) 7.1 Hz, 3 H), 1.05 (s, 3 H),
0.88 (s, 9 H), 0.02 (s, 6 H); 13C NMR δ 177.1 (C), 167.6 (C),
107.5 (CH), 69.1 (CH), 59.4 (CH2), 50.4 (CH3), 45.7 (C), 36.0
(CH2), 34.4 (CH2), 29.6 (CH2), 25.7 (3 × CH3), 23.4 (CH2), 21.1
(CH3), 18.0 (C), 17.5 (CH2), 14.4 (CH), -4.9 (CH3), -5.2 (CH3);
MS (EI) m/z 352 (M+, 6), 337 (M+ - CH3, 3), 307 (M+ - C2H5O,
5), 295 (100); HRMS (EI) calcd for C20H36O3Si 352.2434 (M+),
found 352.2432.
side with respect to the 1R,25-(OH)2-D3 side chain. For the C20
epimers 6b and 8b, the C25-OH groups are located toward the
left side of the side chain of the natural hormone. This
observations suggest that the greater activity of the 20-epi
compounds in the VDR binding and HL-60 cell differentiation
assays, may have been due to the paths of the corresponding
side chains in the VDR-LBD region in agreement with the
results obtained by Dino Moras and co-workers22 on 20-epi
superagonists MC1288 and KH1060. The 20-epi analogues 6b
and 8b interfere hydrophobically stronger with the amino acid
residues located at the right side of the VDR-LBD than the
analogues with the natural stereochemistry at C20.
(17E)-(8â)-8-[(tert-Butyldimethylsilyl)oxy]-des-A,B-pregn-17-
(20)-en-21-ol (16). A solution of DIBALH in heptane (4.1 mL,
3.7 mmol, 1 M) was added slowly to a solution of 15 (0.65 g,
1.85 mmol) in dry toluene (20 mL) at -78 °C. The reaction mixture
was allowed to reach rt for 14 h. The reaction was quenched by
addition of an aqueous solution of HCl (10%, 40 mL). The aqueous
phase was extracted with Et2O (2 × 25 mL). The combined organic
phase was washed with a saturated solution of NaHCO3 (50 mL)
and a saturated solution of NaCl (50 mL), dried, filtered, and
concentrated. The residue was purified by flash chromatography
(10% EtOAc/hexanes) to afford 16 [0.56 g, 97%,Rf ) 0.3 (20%
Conclusions
In conclusion, we synthesized six new calcitriol analogues
conformationally restricted at their side chain by the introduction
of both a cyclopropane ring at C17-C20 and a double or triple
bond at C22, using a divergent route to generate both epimers
at C20, starting from ketone 14. Further studies on the
conformational analysis and biological tests show that com-
pounds 6a/b, 7a/b, and 8a/b do not bind to vitamin D binding
protein (DBP), apparently because their conformationally
restricted C17 side chains are unable to reach the DBP-bound
25-OH-D3 binding region. Compounds 6a, 7a, and 8b also fail
to bind to the vitamin D receptor (VDR), which in the case of
the alkynes 7a and 7b may be due to the high rigidity of their
side chains and to the impossibility of rotation about C17-
C20. However, the remaining three compounds bind to VDR
with affinities that increase in the order 6b(75) < 8a(116) <
8b(176) (numbers in parentheses are percentages of the affinity
of calcitriol for VDR). The 20-epi compounds 6b and 8b bind
to VDR better than to their counterparts 6a and 8a. This result
is attributable to their C20 stereochemistry, allowing them to
lie in the VDR ligand-binding pocket in such a way as to be
able to form strong interactions with hydrophobic amino acids.
The fact that 8a binds well to VDR but does not inhibit the
growth of HL-60 cells suggests that it may be an antagonist or
non-agonist. The compounds 8a and 8b bind best to VDR.
20-Epi compounds induce higher VDR affinities and HL-60 cell
differentiation activities than the corresponding compounds with
the natural stereochemistry at C20. Finally, the fact that the
VDR-active compounds do not bind to DBP suggests that their
local administration for treatment of antiproliferative disease
would not be accompanied by side effects requiring their
transport in the bloodstream, such as hypercalcemia.
1
EtOAc/hexanes), colorless oil]. H NMR δ 5.16 (m, 1 H), 4.07
(m, 3 H), 2.29 (m, 2 H), 1.00 (s, 3 H), 0.88 (s, 9 H), 0.02 (s, 3 H),
0.01 (s, 3 H); 13C NMR δ 156.6 (C), 114.3 (CH), 69.2 (CH), 60.2
(CH2), 50.9 (CH), 43.5 (C), 36.5 (CH2), 34.6 (CH2), 25.8 (3 ×
CH3), 25.3 (CH2), 23.3 (CH2), 21.5 (CH3), 18.0 (CH2), 17.5 (C),
-4.9 (CH3),-5.2 (CH3); MS (FAB) m/z 333 (M+ + Na, 19), 310
(M+, 3), 309 (M+ - H, 14), 293 (100); HRMS (FAB) calcd for
C18H34O2NaSi 333.2226 (M+ + Na), found 333.2226.
(8â)-(20S)-8-[(tert-Butyldimethylsilyl)oxy]-des-A,B-17R,21-cy-
clo-23,24-dinorcholan-22-ol (13a). A solution of Et2Zn in toluene
(30.3 mL, 1 M) was slowly added to a solution of 16 (1.88 g,
6.06 mmol) and CH2I2 (2.44 mL, 30.3 mmol, filtered through
Al2O3), in dry toluene (50 mL) at -78 °C. The reaction was allowed
to reach rt for 5 h and then quenched by the addition of an aqueous
solution of HCl (5%, 50 mL). The aqueous phase was extracted
with Et2O (3 × 40 mL), and the combined organic phase was dried,
filtered, and concentrated. The residue was purified by flash
chromatography (4% EtOAc/hexanes) to give 13a [1.51 g, 77%,
1
Rf ) 0.4 (20% EtOAc/hexanes), white solid, mp 75-78 °C]. H
NMR δ 4.06 (m, 1 H), 3.61 (m, 1 H), 3.48 (m, 1 H), 2.04 (m, 1
H), 1.00 (s, 3 H), 0.89 (s, 9 H), 0.02 (s, 3 H), 0.01 (s, 3 H); 13C
NMR δ 69.0 (CH), 65.2 (CH2), 51.4 (CH), 40.4 (C), 37.1 (C), 34.7
(CH2), 33.7 (CH2), 28.3 (CH2), 25.8 (3 × CH3), 23.5 (CH2), 19.6
(CH), 19.4 (CH3), 18.0 (C), 17.1 (CH2), 16.5 (CH2), -4.8 (CH3),
-5.2 (CH3); MS (EI) m/z 309 (M+ - CH3, 1), 209 (100); HRMS
(EI) calcd for C19H36O2Si 324.2485 (M+), found 324.2483.
(8â)-(20R)-8-[(tert-Butyldimethylsilyl)oxy]-des-A,B-17R,20R-
epoxypregnan-21-ol (17). A solution of t-BuOOH in decane
(0.350 mL, 1.77 mmol, 5 M) was slowly added to a solution of 16
(0.5 g, 1.61 mmol) and a catalytic amount of VO(acac)2 in toluene
(7.5 mL) at -20 °C. The reaction was stirred at the same
temperature for 24 h and then quenched by the addition of a
saturated solution of NaHCO3 (10 mL). The aqueous phase was
extracted with Et2O (3 × 10 mL), and the organic phase was dried,
filtered, and concentrated. The residue was purified by flash
chromatography (10% EtOAc/hexanes, 1% of Et3N) to afford 17
Experimental Section
(17E)-(8â)-8-[(tert-Butyldimethylsilyl)oxy]-des-A,B-pregn-17-
(20)-en-21-oic acid ethyl ester (15). A solution of NaOEt in EtOH
(106 mmol, 65 mL) was added to a mixture of the ketone 14 (3 g,
10.63 mmol) and (EtO)2P(O)CH2CO2Et (53.17 mmol, 10.6 mL,
freshly distilled). The mixture was refluxed for 12 h and then
concentrated to small volume. H2O (60 mL) and HOAc were added
till pH ) 5. The resulting mixture was extracted with Et2O
(3 × 50 mL). The combined organic phase was dried, filtered, and
concentrated. The residue was purified by flash chromatography
1
[0.41 g, 78%, Rf ) 0.3 (30% EtOAc/hexanes), colorless oil]. H
NMR δ 4.10 (m, 1 H), 3.82 (dd, J ) 12.2 and 3.5 Hz, 1 H), 3.55
(dd, J ) 12.2 and 7.0 Hz, 1 H), 3.02 (dd, J ) 7.0 and 3.5 Hz,
1 H), 2.15 (m, 1 H), 1.01 (s, 3 H), 0.88 (s, 9 H), 0.02 (s, 3 H), 0.01
(s, 3 H); 13C NMR δ 74.6 (C), 69.0 (CH), 62.7 (CH2), 57.6 (CH),
49.2 (CH), 41.4 (C), 34.3 (CH2), 30.8 (CH2), 26.8 (CH2), 25.7 (3
× CH3), 22.6 (CH2), 18.5 (CH3), 18.0 (C), 16.5 (CH2), -4.8 (CH3),
-5.2 (CH3); MS (EI) m/z 326 (M+, 1), 311 (M+ - CH3, 1),
(20) (a) Bouillon, R.; Van Baelen, H.; De Moor, P. J. Steroid Biochem.
1980, 13, 1029-1034. (b) Zhou, X.; Zhu, G.-D.; Van Haver, D.; Vande-
walle, M.; De Clercq, P. J.; Verstuyf, A.; Bouillon, R. J. Med. Chem. 1999,
42, 3539-3556.
(21) Ostrem, V. K.; Tanaka, Y.; Prahl, J.; DeLuca, H. F.; Ikekawa, N.
Proc. Natl. Acad. Sci. U.S.A. 1987, 84, 2610-2614.
(22) Tocchini-Valentini, G.; Rochel, N.; Wurtz, J. M.; Mitschler, A.;
Moras, D. Proc. Natl. Acad. Sci. U.S.A. 2001, 98, 5491-5496.
5482 J. Org. Chem., Vol. 72, No. 15, 2007

17R,21-Cyclo-22-Unsaturated Analogues of Calcitriol
269 (M+ - C4H9, 30), 75 (100); HRMS (EI) calcd for C14H25O3Si
269.1573 (M+ - C4H9), found 269.1574.
(3 × CH3), 23.5 (CH2), 20.6 (CH), 19.6 (CH2), 18.9 (CH3), 18.0
(C), 17.1 (CH2), -4.8 (CH3), -5.1 (CH3); MS (FAB) m/z 393 (M+
+ H, 4), 392 (M+, 4), 391 (M+ - H, 8), 209 (100); HRMS (FAB)
calcd for C24H43O2Si 391.3032 (M+ - H), found 391.3028.
To a solution of the above alcohol (500 mg, 1.28 mmol) was
added MOMCl (0.32 mL, 3.8 mmol) and i-Pr2NEt (0.67 mL, 3.8
mmol) in CH2Cl2 (25 mL) at 0 °C. The reaction mixture was stirred
for 24 h. The reaction was quenched by the addition of ice and an
aqueous solution of HCl (10%). The resulting mixture was extracted
with CH2Cl2 and the resulting organic layer was washed with H2O,
dried, filtered, and concentrated. The residue was purified by flash
chromatography (5% EtOAc/hexanes) to give 21a [513 mg, 92%,
(17Z)-(8â)-8-[(tert-Butyldimethylsilyl)oxy]-des-A,B-pregn-17-
(20)-en-21-ol (18). A solution of n-BuLi in hexanes (1.2 mL,
3.0 mmol, 2.5 M) was slowly added to a solution of Ph2PH (0.49
mL, 2.83 mmol) in dry THF (2 mL) at 0 °C. The resulting red
mixture was protected from light and stirred for 4 h. A solution of
17 (0.350 g, 1.07 mmol) in dry THF (3 mL) was added, and the
resulting mixture was stirred for 1 h. MeI (0.31 mL, 5.1 mmol,
filtered through Al2O3) was added, and the mixture was stirred for
4 h at rt. The reaction was quenched by the addition of H2O. The
white suspension was filtered and the solids were washed with Et2O
(4 × 10 mL). The organic solution was dried, filtered, and
concentrated. The residue was purified by flash chromatography
(10% EtOAc/hexanes) to give 18 [0.273 g, 82%, Rf ) 0.7 (30%
EtOAc/hexanes), white solid, mp 53-55 °C]. 1H NMR δ 5.23 (dd,
J ) 7.3 and 7.1 Hz, 1 H), 4.29 (dd, J ) 12.2 and 7.3 Hz, 1 H),
4.14 (dd, J ) 12.2 and 7.1 Hz, 1 H), 4.07 (m, 1 H), 2.45 (m, 1 H),
2.20 (m, 2 H), 1.12 (s, 3 H), 0.89 (s, 9 H), 0.02 (s, 3 H), 0.01 (s,
3 H); 13C NMR δ 155.0 (C), 117.9 (CH), 69.6 (CH), 58.7 (CH2),
52.3 (CH), 44.6 (C), 38.1 (CH2), 34.2 (CH2), 30.6 (CH2), 25.8 (3
× CH3), 23.5 (CH2), 20.5 (CH3), 18.0 (C), 17.8 (CH2), -4.8 (CH3),
-5.1 (CH3); MS (EI) m/z 310 (M+, 1), 295 (M+ - CH3, 1), 75
(100); HRMS (EI) calcd for C18H34O2Si 310.2328 (M+), found
310.2333.
1
Rf ) 0.7 (15% EtOAc/hexanes), colorless oil]. H NMR δ 5.47
(dt, J ) 15.2 and 7.3 Hz, 1 H), 5.10 (dd, J ) 15.2 and 8.7 Hz, 1
H), 4.72 (s, 2 H), 4.05 (m, 1 H), 3.36 (s, 3 H), 2.21 (d, J ) 7.3 Hz,
2 H), 1.99 (m, 1 H), 1.19 (s, 6 H), 0.95 (s, 3 H), 0.88 (s, 9 H), 0.08
(br d, J ) 4.8 Hz, 1 H), 0.01 (s, 3 H), 0.00 (s, 3 H); 13C NMR δ
135.3 (CH), 124.1 (CH), 91.0 (CH2), 76.4 (C), 69.1 (CH), 55.0
(CH3), 51.5 (CH), 45.1 (CH2), 41.0 (C), 38.7 (C), 34.7 (CH2), 33.8
(CH2), 28.9 (CH2), 26.1 (2 × CH3), 25.8 (3 × CH3), 23.5 (CH2),
20.6 (CH), 19.4 (CH2), 18.8 (CH3), 18.0 (C), 17.1 (CH2), -4.8
(CH3), -5.2 (CH3); MS (FAB) m/z 435 (M+ - H, 8), 405 (M+
-
CH3O, 7), 209 (89), 109 (100); HRMS (FAB) calcd for C25H45O2-
Si 405.3189 (M+ - CH3O), found 405.3192.
(8â)-(20S)-8-[(tert-Butyldimethylsilyl)oxy]-des-A,B-17R,21-cy-
clo-24-norchol-22-yne (22a). A solution of aldehyde 19a (0.485
g, 1.58 mmol) in CH2Cl2 (16 mL) and pyridine (1.3 mL, 16.3 mmol)
were successively added to a mixture of Zn (0.633 g, 9.7 mmol),
CBr4 (3.2 g, 9.7 mmol), and Ph3P (2.54 g, 9.7 mmol) in CH2Cl2
(30 mL). The reaction mixture was stirred for 5 h. The reaction
was quenched by the addition of Et2O (50 mL). The suspension
was filtered through celite and the solids were washed with Et2O.
The organic layer was concentrated and the residue was purified
by flash chromatography (hexanes) to afford (8â)-(20R)-8-[(tert-
butyldimethylsilyl)oxy]-des-A,B-17R,21-cyclo-23,23-dibromo-24-
norchol-22-ene [714 mg, 94%, Rf ) 0.8 (5% EtOAc/hexanes), white
(8â)-(20S)-8-[(tert-Butyldimethylsilyl)oxy]-des-A,B-17R,21-cy-
clo-23,24-dinorcholan-22-al (19a). Dry DMSO (0.253 mL, 3.57
mmol) was slowly added to a solution of oxalyl chloride (0.160
mL, 1.79 mmol) in dry CH2Cl2 (20 mL) at -78 °C. The solution
was stirred for 15 min. A solution of 13a (0.455 g, 1.41 mmol) in
dry CH2Cl2 (9 mL) was added. The mixture was stirred at -78 °C
for 0.5 h, and Et3N (2 mL, 14.1 mmol) was added. The mixture
was allowed to reach rt for 7 h. The reaction was quenched by the
addition of H2O (40 mL) and CH2Cl2 (40 mL). The organic phase
was washed with brine (40 mL), dried, filtered, and concentrated.
The residue was purified by flash chromatography (5% EtOAc/
hexanes) to afford 19a [0.413 g, 91%, Rf ) 0.6 (20% EtOAc/
1
solid, mp 52-54 °C]. H NMR δ 5.94 (d, J ) 9.3 Hz, 1 H), 4.07
1
(m, 1 H), 2.04 (m, 1 H), 1.03 (s, 3 H), 0.89 (s, 9 H), 0.32 (br d, J
) 5.0 Hz, 1 H), 0.02 (s, 3 H), 0.01 (s, 3 H); 13C NMR δ 140.7
(CH), 84.7 (C), 68.9 (CH), 51.2 (CH), 40.9 (C), 40.4 (C), 34.5
(CH2), 33.8 (CH2), 29.4 (CH2), 25.8 (3 × CH3), 23.5 (CH2), 22.4
(CH), 21.0 (CH2), 19.6 (CH3), 18.0 (C), 17.0 (CH2), -4.8 (CH3),
-5.2 (CH3); MS (EI) m/z 476 (M+, 2), 463 (41), 421 (80), 209
(100); HRMS (EI) calcd for C20H34OSiBr2 476.0746 (M+), found
476.0750.
hexanes), white solid, mp 120-123 °C]. H NMR δ 9.08 (d, J )
6.3 Hz, 1 H), 4.08 (m, 1 H), 2.04 (m, 1 H), 1.02 (s, 3 H), 0.88 (s,
9 H), 0.02 (s, 3 H), 0.01 (s, 3 H); 13C NMR δ 202.0 (CH), 68.8
(CH), 50.5 (CH), 44.5 (C), 41.6 (C), 34.5 (CH2), 33.6 (CH2), 30.9
(CH), 28.8 (CH2), 25.8 (3 × CH3), 23.5 (CH2), 21.2 (CH2), 19.3
(CH3), 18.0 (C), 17.0 (CH2), -4.8 (CH3), -5.2 (CH3); MS (EI)
m/z 323 (M+ + H, 7), 322 (M+, 12), 307 (M+ - CH3, 34), 209
(100); HRMS (EI) calcd for C19H34O2Si 322.2328 (M+), found
322.2316.
A solution of n-BuLi in hexanes (0.45 mL, 0.96 mmol, 2.1 M)
was slowly added to a solution of the above dibromide (0.139 g,
0.29 mmol) in THF (10 mL), at -78 °C. After stirring for 0.5 h,
the reaction was quenched with MeOH. The mixture was concen-
trated and diluted with brine. The mixture was extracted with Et2O
(25 mL). The organic phase was dried, filtered, and concentrated.
The residue was purified by flash chromatography (hexanes) to give
22a [790 mg, 85%, Rf ) 0.5 (hexanes), white solid, mp 62-64
°C]. 1H NMR δ 4.06 (s, 1 H), 2.27 (m, 1 H), 1.83 (s, 1 H), 1.02 (s,
3 H), 0.89 (s, 9 H), 0.38 (br s, 1 H), 0.02 (s, 6 H); 13C NMR δ 86.3
(C), 69.1 (CH), 65.4 (CH), 52.2 (CH), 40.5 (C), 39.2 (C), 34.5
(CH2), 33.9 (CH2), 29.9 (CH2), 25.8 (3 × CH3), 23.4 (CH2), 21.0
(CH2), 19.3 (CH3), 18.0 (C), 17.0 (CH2), 6.5 (CH), -4.8 (CH3),
-5.2 (CH3); MS (EI) m/z 303 (M+ - CH3, 1), 261 (5), 209 (100);
HRMS (EI) calcd for C20H34OSi 318.2379 (M+), found
318.2367.
(8â)-(20S)-8-[(tert-Butyldimethylsilyl)oxy]-des-A,B-17R,21-cy-
clocholest-22-yn-25-ol (23a). A solution of n-BuLi in hexanes (1
mL, 2.26 mmol, 2.27 M) was slowly added to a solution of 22a
(0.654 g, 2.05 mmol) in THF (30 mL) at -78 °C. After 30 min,
BF3‚OEt2 (1.26 mL, 10.2 mmol) and a solution of isobutylene oxide
(0.92 mL, 10.3 mmol) in THF (12 mL) were successively added.
After stirring for 6 h at rt, the reaction was quenched with a few
drops of MeOH. The mixture was extracted with Et2O (100 mL).
(22E)-(8â)-(20R)-8-[(tert-Butyldimethylsilyl)oxy]-25-[(meth-
oxymethyl)oxy]-des-A,B-17R,21-cyclocholest-22-ene (21a). A so-
lution of MeLi in Et2O (0.81 mL, 1.3 mmol, 1.6 M) was added to
a solution of the phosphonium salt Ph3P+CH2CH2CMe2OH Br-
(20, 0.28 g, 0.65 mmol) in THF (5 mL) at -20 °C. The red mixture
was stirred for 1.5 h at -20 °C and 8 h at rt. After cooling to -30
°C, a solution of 19a (0.100 g, 0.33 mmol) in THF (4 mL) was
slowly added. After stirring for 12 h, the reaction was quenched
with H2O (10 mL). The mixture was filtered through celite. The
filtrate was extracted with Et2O, and the resulting organic layer
was washed with brine, dried, filtered, and concentrated. The residue
was purified by flash chromatography (10% EtOAc/hexanes) to
give a mixture of isomers (E:Z ) 7.5:1), which were separated by
HPLC (Phenomenex, Zorbax Silica, SP/6885B; 2% i-PrOH/
hexanes; 2 mL/min) to afford (22E)-(8â)-(20R)-8-[(tert-butyldi-
methylsilyl)oxy]-des-A,B-17R,21-cyclocholest-22-en-25-ol [0.105
g, 82%, Rf ) 0.4 (15% EtOAc/hexanes), colorless oil]. 1H NMR δ
5.50 (dt, J ) 15.2 and 7.5 Hz, 1 H), 5.17 (dd, J ) 15.2 and 8.8 Hz,
1 H), 4.05 (m, 1 H), 2.15 (d, J ) 7.5 Hz, 2 H), 1.98 (m, 1 H), 1.19
(s, 6 H), 0.96 (s, 3 H), 0.88 (s, 9 H), 0.11 (dd, J ) 5.0 Hz, 1 H),
0.01 (s, 3 H), 0.00 (s, 3 H); 13C NMR δ 137.0 (CH), 123.4 (CH),
70.3 (C), 69.1 (CH), 51.5 (CH), 46.9 (CH2), 41.0 (C), 38.9 (C),
34.6 (CH2), 33.8 (CH2), 29.0 (CH2), 29.0 (CH3), 28.9 (CH3), 25.7
J. Org. Chem, Vol. 72, No. 15, 2007 5483

Riveiros et al.
The organic phase was washed with NaHCO3 (50 mL) and brine
(50 mL), dried, filtered, and concentrated. The residue was purified
by flash chromatography (10% EtOAc/hexanes) to afford 23a [703
mg, 88%, Rf ) 0.4 (15% EtOAc/hexanes), colorless oil]. 1H NMR
δ 4.06 (s, 1 H), 2.33 (d, J ) 1.2 Hz, 2 H), 2.20 (m, 1 H), 1.27 (s,
6 H), 1.01 (s, 3 H), 0.89 (s, 9 H), 0.30 (br d, J ) 3.2 Hz, 1 H),
0.02 (s, 6 H); 13C NMR δ 85.2 (C), 73.6 (C), 69.8 (C), 69.1 (CH),
52.1 (CH), 40.5 (C), 39.2 (C), 34.7 (CH2), 34.5 (CH2), 33.9 (CH2),
30.3 (CH2), 28.5 (2 × CH3), 25.8 (3 × CH3), 23.4 (CH2), 21.1
(CH2), 19.3 (CH3), 18.0 (C), 17.0 (CH2), 6.8 (CH), -4.8 (CH3),
-5.2 (CH3); MS (EI) m/z 390 (M+, 1), 375 (M+ - CH3, 9), 209
(100); HRMS (EI) calcd for C24H42O2Si 390.2954 (M+), found
390.2950.
(8â)-(20S)-8-[(tert-Butyldimethylsilyl)oxy]-25-[(methoxymethyl)-
oxy]-des-A,B-17R,21-cyclocholest-22-yne (24a). MOMCl (0.25
mL, 3.3 mmol) and i-Pr2NEt (0.6 mL, 3.3 mmol) were added to a
solution of 23a (433 mg, 1.11 mmol) in CH2Cl2 (10 mL) at 0 °C.
After stirring for 24 h, the reaction was quenched with ice and an
aqueous solution of HCl (10%). The resulting mixture was extracted
with CH2Cl2 (15 mL). The organic phase was washed with H2O,
dried, filtered, and concentrated. The residue was purified by flash
chromatography (5% EtOAc/hexanes) to give 24a [330 mg, 92%,
Rf ) 0.7 (15% EtOAc/hexanes), colorless oil]. 1H NMR δ 4.72 (s,
2 H), 4.04 (m, 1 H), 3.35 (s, 3 H), 2.38 (d, J ) 1.3 Hz, 2 H), 2.22
(m, 1 H), 1.29 (s, 6 H), 0.99 (s, 3 H), 0.88 (s, 9 H), 0.26 (br d, J
) 3.5 Hz, 1 H), 0.00 (s, 6 H); 13C NMR δ 91.2 (CH2), 83.6 (C),
76.0 (C), 74.2 (C), 69.1 (CH), 55.1 (CH3), 52.1 (CH), 40.4 (C),
39.1 (C), 34.5 (CH2), 33.9 (CH2), 32.5 (CH2), 30.1 (CH2), 25.9 (2
× CH3), 25.8 (3 × CH3), 23.4 (CH2), 21.0 (CH2), 19.2 (CH3), 18.0
(C), 17.0 (CH2), 6.9 (CH), -4.8 (CH3), -5.2 (CH3); MS (EI) m/z
419 (M+ - CH3, 3), 403 (M+ - CH3O, 8), 209 (100); HRMS (EI)
calcd for C26H46NaO3Si 457.3114 (M+), found 457.3108.
(22Z)-(8â)-(20R)-8-[(tert-Butyldimethylsilyl)oxy]-25-[(meth-
oxymethyl)oxy]-des-A,B-17R,21-cyclocholest-22-ene (25a). A mix-
ture of quinoline (0.018 g, 0.14 mmol), Lindlar catalyst (0.050 g),
and 23a (0.070 g, 0.18 mmol) in dry hexane (70 mL) was
hydrogenated for 30 min (balloon pressure). The mixture was
filtered through a short pad of celite. Concentration gave a residue
which was purified by flash chromatography (5% EtOAc/hexanes)
to afford (22Z)-(8â)-(20R)-8-[(tert-butyldimethylsilyl)oxy]-des-A,B-
17R,21-cyclocholest-22-en-25-ol [61 mg, 87%, Rf ) 0.4 (15%
EtOAc/hexanes), colorless oil]. 1H NMR δ 5.42 (dt, J ) 10.9 and
7.5 Hz, 1 H), 5.14 (dd, J ) 10.8 and 9.9 Hz, 1 H), 4.06 (m, 1 H),
2.33 (d, J ) 7.7 Hz, 2 H), 2.03 (m, 1 H), 1.29 (s, 6 H), 0.98 (s, 3
H), 0.88 (s, 9 H), 0.10 (br d, J ) 4.6 Hz, 1 H), 0.02 (s, 6 H); 13C
NMR δ 135.7 (CH), 122.9 (CH), 71.2 (C), 69.1 (CH), 51.4 (CH),
41.4 (CH2), 41.0 (C), 39.4 (C), 34.7 (CH2), 34.0 (CH2), 29.2 (CH3),
29.0 (CH3), 28.9 (CH2), 25.8 (3 × CH3), 23.5 (CH2), 20.9 (CH2),
19.3 (CH3), 18.0 (C), 17.1 (CH2), 16.5 (CH), -4.8 (CH3), -5.2
(CH3); MS (FAB) m/z 393 (M+ + H, 24), 392 (M+, 27), 391 (M+
- H, 67), 377 (M+ - CH3, 11), 375 (75), 265 (100); HRMS (FAB)
calcd for C24H44O2Si 392.3116 (M+), found 392.3092.
Protection of the above alcohol, following the same experimental
procedure as for 24a, afforded 25a [92%, Rf ) 0.7 (15% EtOAc/
hexanes), colorless oil]. 1H NMR δ 5.39 (dt, J ) 10.9 and 7.5 Hz,
1 H), 5.06 (dd, J ) 10.9 and 9.8 Hz, 1 H), 4.74 (s, 2 H), 4.06 (m,
1 H), 3.37 (s, 3 H), 2.37 (d, J ) 7.4 Hz, 2 H), 2.01 (m, 1 H), 1.24
(s, 6 H), 0.97 (s, 3 H), 0.88 (s, 9 H), 0.07 (br d, J ) 4.8 Hz, 1 H),
0.01 (s, 3 H), 0.01 (s, 3 H); 13C NMR δ 133.9 (CH), 123.6 (CH),
91.1 (CH2), 76.7 (C), 69.1 (CH), 55.0 (CH3), 51.4 (CH), 41.0 (C),
39.5 (CH2), 39.2 (C), 34.7 (CH2), 34.0 (CH2), 28.8 (CH2), 26.3
(CH3), 26.1 (CH3), 25.8 (3 × CH3), 23.5 (CH2), 20.7 (CH2), 19.4
(CH3), 18.0 (C), 17.1 (CH2), 16.5 (CH), -4.8 (CH3), -5.2 (CH3);
MS (FAB) m/z 435 (M+ - H, 7), 405 (M+ - CH3O, 8), 109 (100);
HRMS (FAB) calcd for C25H45O2Si 405.3189 (M+ - CH3O), found
405.3190.
mmol) in THF (15 mL). The mixture was refluxed for 12 h and
then treated with saturated aqueous NaHCO3 (5 mL). The aqueous
phase was extracted with Et2O (30 mL), and the combined organic
phase was dried, filtered, and concentrated. The residue was purified
by flash chromatography (5% EtOAc/hexanes) to give 26a [280
mg, 95%, Rf ) 0.4 (25% EtOAc/hexanes), colorless oil]. 1H NMR
δ 5.45 (dt, J ) 15.2 and 7.2 Hz, 1 H), 5.07 (dd, J ) 15.3 and 8.7
Hz, 1 H), 4.69 (s, 2 H), 4.09 (m, 1 H), 3.33 (s, 3 H), 2.19 (d, J )
7.2 Hz, 2 H), 2.00 (m, 1 H), 1.16 (s, 6 H), 0.96 (s, 3 H), 0.08 (br
d, J ) 5.0 Hz, 1 H); 13C NMR δ 134.8 (CH), 124.3 (CH), 90.9
(CH2), 76.3 (C), 68.8 (CH), 54.9 (CH3), 51.0 (CH), 45.0 (CH2),
40.6 (C), 38.6 (C), 33.7 (CH2), 33.5 (CH2), 28.7 (CH2), 26.0 (2 ×
CH3), 22.9 (CH2), 20.5 (CH), 19.3 (CH2), 18.4 (CH3), 16.8 (CH2);
MS (FAB) m/z 345 (M+ + Na, 4), 291 (M+ - CH3O, 14), 109
(100); HRMS (FAB) calcd for C20H34O3Na 345.2406 (M+ + Na),
found 345.2399.
(22E)-(20R)-25-[(Methoxymethyl)oxy]-des-A,B-17R,21-cyclo-
cholest-22-en-8-one (9a). Pyridinium dichromate (450 mg, 1.20
mmol) and pyridinium p-toluenesulfonate (25 mg) were added to
a solution of 26a (227 mg, 0.71 mmol) in CH2Cl2 (10 mL). After
8 h, Et2O (40 mL) was added and the resulting mixture was filtered
through Celite. Concentration after washing the solids with Et2O
(3 × 40 mL) gave a residue which was purified by flash
chromatography (10% EtOAc/hexanes) to afford 9a [203 mg, 90%,
1
Rf ) 0.5 (25% EtOAc/hexanes), colorless oil]. H NMR δ 5.44
(dt, J ) 15.2 and 7.5 Hz, 1 H), 5.06 (dd, J ) 15.2 and 8.6 Hz, 1
H), 4.68 (s, 2 H), 3.32 (s, 3 H), 2.62 (dd, J ) 11.1 and 7.4 Hz, 1
H), 2.18 (d, J ) 7.2 Hz, 2 H), 1.15 (s, 6 H), 0.67 (s, 3 H), 0.20 (br
d, J ) 5.2 Hz, 1 H); 13C NMR δ 211.4 (C), 133.9 (CH), 125.1
(CH), 90.9 (CH2), 76.2 (C), 60.2 (CH), 54.9 (CH3), 48.5 (C), 45.0
(CH2), 40.9 (CH2), 37.8 (C), 32.8 (CH2), 28.7 (CH2), 26.0 (2 ×
CH3), 23.1 (CH2), 21.2 (CH), 19.8 (CH2), 19.0 (CH2), 16.9 (CH3);
MS (FAB) m/z 343 (M+ + Na, 6), 289 (M+ - CH3O, 31), 150
(100); HRMS (FAB) calcd for C20H32O3Na 343.2249 (M+ + Na),
found 343.2236.
(5Z,7E,22E)-(1S,3R,20R)-17R,21-cyclo-9,10-secocholesta-5,7,-
10(19),22-tetraene-1,3,25-triol (6a). A solution of n-BuLi in
hexanes (0.200 mL, 0.45 mmol, 2.26 M) was added dropwise to a
solution of 12 (283 mg, 0.49 mmol) at -78 °C. The resulting deep
red solution was stirred at -78 °C for 1 h followed by the slow
addition of a solution of 9a (82 mg, 0.26 mmol) in THF (3 mL).
The red solution was stirred in the dark at -78 °C for 3 h and then
warmed to -40 °C over 2 h. The reaction was quenched with H2O
(5 mL). The mixture was extracted with Et2O (30 mL) and the
organic phase was washed with brine, dried, filtered, and concen-
trated. The residue was purified by flash chromatography (2%
EtOAc/hexanes) to give (5Z,7E,22E)-(1S,3R,20R)-1,3-di-[(tert-
butyldimethylsilyl)oxy]-25-[(methoxymethyl)oxy]-17R,21-cyclo-9,-
10-secocholesta-5,7,10(19),22-tetraene [150 mg, 86%, (22E:22Z )
8:1), Rf ) 0.7 (5% EtOAc/hexanes), colorless oil]. 1H NMR δ 6.24
and 6.06 (2 d, AB system, J ) 11.1 Hz, 2 H), 5.46 (dt, J ) 15.2
and 7.5 Hz, 1 H), 5.19 (br s, 1 H), 5.12 (dd, J ) 15.2 and 8.6 Hz,
1 H), 4.88 (br s, 1 H), 4.72 (s, 2 H), 4.38 (m, 1 H), 4.19 (m, 1 H),
2.84 (m, 1 H), 2.23 (d, J ) 7.3 Hz, 2 H), 1.20 (s, 6 H), 0.88 (s, 18
H), 0.59 (s, 3 H), 0.16 (d, J ) 5.0 Hz, 1 H), 0.06 (s, 12 H); 13C
NMR δ 148.3 (C), 140.8 (C), 135.2 (C), 135.0 (CH), 124.3 (CH),
123.1 (CH), 117.8 (CH), 111.2 (CH2), 91.0 (CH2), 76.4 (C), 72.0
(CH), 67.5 (CH), 55.0 (CH3), 54.6 (CH), 46.0 (CH2), 45.1 (CH2),
44.8 (CH2), 44.5 (C) 38.0 (C), 34.3 (CH2), 29.0 (CH2), 28.8 (CH2),
26.1 (CH3), 25.8, 25.8 (6 × CH3), 23.0 (CH2), 22.8 (CH2), 22.6
(C), 21.1 (CH), 19.4 (CH2), 18.2 (C), 18.1 (C), 16.7 (CH3), -4.7
(CH3), -4.7 (CH3), -4.8 (CH3), -5.1 (CH3); MS (FAB) m/z 685
(M+ + H, 12), 684 (M+, 10), 653 (M+ - CH3O, 9), 133 (100);
HRMS (FAB) calcd for C40H69O3Si2 653.4785 (M+ - CH3O),
found 653.4787.
A solution of n-Bu4F in THF (2.5 mL, 2.5mmol, 1 M) was added
via syringe to a solution of the protected vitamin D analogue (85
mg, 0.12 mmol) in THF (3 mL). After stirring in the dark at rt for
12 h, a saturated solution of NH4Cl (10 mL) was added. The
(22E)-(8â)-(20R)-25-[(Methoxymethyl)oxy]-des-A,B-17R,21-
cyclocholest-22-en-8-ol (26a). A solution of n-Bu4NF in THF (9
mL, 9 mmol, 1 M) was added to a solution of 21a (400 mg, 0.92
5484 J. Org. Chem., Vol. 72, No. 15, 2007

17R,21-Cyclo-22-Unsaturated Analogues of Calcitriol
resulting mixture was extracted with Et2O (3 × 15 mL). The
resulting organic phase was dried, filtered, and concentrated.
The residue was dissolved in deoxygenated MeOH (3 mL) and
treated with cationic resin AG 50W-X4 (1 g, prewashed with
MeOH). The mixture was stirred at rt for 5 h in the dark. Filtration
and concentration gave a residue which was purified by flash
chromatography (60% EtOAc/hexanes) to afford vitamin D ana-
logue 6a [45 mg, 88%, Rf ) 0.4 (80% EtOAc/hexanes), white solid].
1H NMR (CD3OD) δ 6.34 and 6.14 (2 d, AB system, J ) 11.1 Hz,
2 H), 5.52 (dt, J ) 15.2 and 7.5 Hz, 1 H), 5.31 (br s, 1 H), 5.13
(dd, J ) 15.2 and 8.5 Hz, 1 H), 4.92 (m, 1 H), 4.37 (m, 1 H), 4.14
(m, 1 H), 1.16 (s, 6 H), 0.64 (s, 3 H), 0.19 (br d, J ) 5.0 Hz, 1 H);
13C NMR (CD3OD) δ 149.7 (C), 142.4 (C), 136.1 (CH), 135.9 (C),
125.9 (CH), 124.8 (CH), 119.0 (CH), 112.1 (CH2), 71.5 (CH), 71.5
(C), 67.4 (CH), 55.9 (CH), 48.1 (CH2), 46.1 (C), 45.7 (CH2), 43.7
(CH2), 39.0 (C), 35.5 (CH2), 30.1 (CH2), 30.0 (CH2), 29.0 (CH3),
28.9 (CH3), 24.1 (CH2), 24.0 (CH2), 22.2 (CH), 20.0 (CH2), 17.2
Acknowledgment. This work was supported by the Spanish
MEC (Projects SAF2001-3187 and SAF2004-1885). R.R. and
A.R. thank the Xunta de Galicia and MEC for the re-
spective “Isidro Parga Pondal” and “Ramo´n y Cajal” contracts.
We also thank CESGA for computing time, Solvay Pharma-
ceuticals BV (Weesp, The Netherlands) for the gift of starting
materials and Dr. Y. Fall for his previous contributions to this
project. The cover was designed by Rita Sigu¨eiro.
Supporting Information Available: General experimental
methods and experimental procedures for the preparation of
compounds 13b, 19b, 21b, 22b, 23b, 24b, 25b, 27a, 10a, 7a, 28a,
11a, 8a, 26b, 9b, 6b, 27b, 10b, 7b, 28b, 11b, and 8b, including
spectroscopic and analytical data. Copies of NMR spectra for
compounds prepared. This material is available free of charge via
the Internet at http://pubs.acs.org.
(CH3); MS (FAB) m/z 413 (M+ + H, 4), 412 (M+, 8), 394 (M+
-
H2O, 8), 286 (22), 137 (100); HRMS (FAB) calcd for C27H40O3
412.2977 (M+), found 412.2971.
JO0625195
J. Org. Chem, Vol. 72, No. 15, 2007 5485