A concise and efficient route to 2alpha-(omega-hydroxyalkoxy)-1alpha,25-dihydroxyvi tam in D3: remarkably high affinity to vitamin D receptor.

Article abstract of DOI:10.1021/ol006222j

[reaction: see text]A convenient and potentially valuable synthetic approach to the novel 2alpha-functionalized 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)2D3] derivatives (1a-c), which are the C2-epimer of ED-71 and its analogues, has been developed. Th

Full text of DOI:10.1021/ol006222j

ORGANIC
LETTERS
2000
Vol. 2, No. 17
2619-2622
A Concise and Efficient Route to
2r-(ω-Hydroxyalkoxy)-1r,25-
dihydroxyvitamin D : Remarkably High
3
Affinity to Vitamin D Receptor1
Atsushi Kittaka,† Yoshitomo Suhara,† Hitoshi Takayanagi,† Toshie Fujishima,†
,†
Masaaki Kurihara,‡ and Hiroaki Takayama*
Faculty of Pharmaceutical Sciences, Teikyo UniVersity,
Sagamiko, Kanagawa 199-0195, Japan, and National Institute of Health Sciences,
Kamiyoga, Setagaya-ku, Tokyo 158-8501, Japan
hi-takay@pharm.teikyo-u.ac.jp
Received June 16, 2000
ABSTRACT
A convenient and potentially valuable synthetic approach to the novel 2r-functionalized 1r,25-dihydroxyvitamin D [1r,25(OH)2D ] derivatives
3
3
(1a−c), which are the C2-epimer of ED-71 and its analogues, has been developed. The C2r-modified ring A precursors (1,7-enynes 16, n )
0, 1, and 2) were constructed stereoselectively starting from D-glucose in high yield. In the synthesized 2r-(ω-hydroxyalkoxy)-1r,25(OH)2D
3
derivatives, 1a and 1b showed a greater binding affinity to vitamin D receptor (VDR), up to 1.8 times that of the native hormone.
The seco-steroid hormone 1R,25-dihydroxyvitamin D3
[1R,25(OH)2D3] is the most potent metabolite of vitamin D3
and regulates primarily calcium homeostasis, as well as cell
proliferation and differentiation and immunology.2 Some of
these biological responses to this class of compounds may
have high potential in the treatment of rickets, renal
osteodystrophy, osteoporosis, psoriasis, certain cancers,
AIDS, and Alzheimer’s disease.2,3 One of the major problems
in the clinical use of 1R,25(OH)2D3 is the effective doses,
which likely induce fatal hypercalcemia.2 The search for a
noncalcemic therapeutic agent, and for convenient synthetic
methods of finely modified compounds, has been greatly
stimulated by medical needs.
2â-(3-Hydroxypropoxy)-1R,25(OH)2D3 (ED-71) was de-
veloped by Chugai Pharmaceutical Co. as a promising
candidate for the treatment of osteoporosis.2,4 Recently, we
reported synthesis of the A-ring modified analogues, 2-meth-
yl-1R,25(OH)2D3, and found that the 2R-isomer 2 showed
higher potency than the native hormone in terms of binding
affinity to vitamin D receptor (VDR), elevation of serum
Ca concentration, and induction of HL 60 cell differentia-
† Teikyo University.
‡ National Institute of Health Sciences.
(1) This paper is dedicated (by A.K.) to Prof. Dr. A. Eschenmoser on
the occasion of his 75th birthday.
(2) (a) Vitamin D; Feldman, D., Glorieux, F. H., Pike, J. W., Eds.;
Academic Press: New York, 1997. (b) Ettinger, R. A.; DeLuca, H. F. AdV.
Drug Res. 1996, 28, 269-312.
(3) Bouillon, R.; Okamura, W. H.; Norman, A. W. Endocr. ReV. 1995,
16, 200-257.
10.1021/ol006222j CCC: $19.00 © 2000 American Chemical Society
Published on Web 08/04/2000

tion.5 Further modification of the 2R-methyl group, in
particular, introduction of the 2R-(3-hydroxypropyl) group
into the A-ring of 1R,25(OH)2D3 (3), increased by 500 times
the potency of calcium-mobilizing activity.6 Most of the
biological actions of 1R,25(OH)2D3 are considered to be
mediated by the vitamin D receptor (VDR), which belongs
to the nuclear receptor superfamily acting as a ligand-
dependent transcription factor with coactivators.7 Accord-
ingly, we planned to synthesize new analogues (1) containing
the hydroxyalkoxyl group at the C2 position, like ED-71 but
with the R-orientation, to understand the detail structure-
activity relationships, particularly on the ring A (Figure 1).
4, which is readily available from methyl R-D-glucoside,8
was chosen as the chiral template. The regiospecific ring
opening9 by a suitable alkanediol4a at the C3 position affords
the altrose configuration, in which C2, C3, and C4 asym-
metric centers satisfy the corresponding desired 3â, 2R, and
1R stereochemistries of 1, respectively. As illustrated in
Scheme 1, for example, n ) 1, 4 was heated with 1,3-
propanediol under basic conditions to yield methyl 3-O-(3-
hydroxypropyl)altropyranoside 5 (n ) 1). After selective
Scheme 1a
Figure 1. Structures of 1R,25-dihydroxyvitamin D3 [1R,25-
(OH)2D3] and its 2R-substituted analogues 1-3.
The original approach to ED-71 from lithocholic acid
allows only 2â-substitution of 1R,25(OH)2D3.4a On the basis
of convergent synthesis, A-ring synthons were elegantly
constructed using a C2 chiral epoxide4b or the adaptation of
a polyol chiron.4c,d We wish to report here a new concise
and efficient synthetic route to 2R-(ω-hydroxyalkoxy)-
1R,25(OH)2D3 derivatives (1a-c) from D-glucose and their
considerable binding affinity to VDR.
To create 1R,2R,3â stereochemistry on the ring A of the
target vitamin D analogues (1), the known crystalline epoxide
(4) (a) Miyamoto, K.; Murayama, E.; Ochi, K.; Watanabe, H.; Kubodera,
N. Chem. Pharm. Bull. 1993, 41, 1111-1113. (b) Hatakeyama, S.; Ikeda,
T.; Maeyama, J.; Esumi, T.; Iwabuchi, Y.; Irie, H.; Kawase, A.; Kubodera,
N. Bioorg. Med. Chem. Lett. 1997, 7, 2871-2874. (c) Moriarty, R. M.;
Brumer, H. Tetrahedron Lett. 1995, 36, 9265-9268. (d) Takahashi, T.;
Nakazawa, M. Synlett 1993, 37-39. (e) Takahashi, T.; Nakazawa, M.;
Sakamoto, Y.; Houk, K. N. Tetrahedron Lett. 1993, 34, 4075-4078. For
biological activities of a series of 2â-substituted analogues, see: (f) Tsugawa,
N.; Nakagawa, K.; Kurobe, M.; Ono, Y.; Kubodera, N.; Ozono, K.; Okano,
T. Biol. Pharm. Bull. 2000, 23, 66-71. Syntheses of 19-nor and 2-(4-
hydroxybutyl) analogues of ED-71 were reported, see: (g) Sicinski, R. F.;
Perlman, K. L.; DeLuca, H. F. J. Med. Chem. 1994, 37, 3730-3738. (h)
Posner, G. H.; Johnson, N. J. Org. Chem. 1994, 59, 7855-7861.
(5) (a) Konno, K.; Maki, S.; Fujishima, T.; Liu, Z.-P.; Miura, D.; Chokki,
M.; Takayama, H. Bioorg. Med. Chem. Lett. 1998, 8, 151-156. (b)
Nakagawa, K.; Kurobe, M.; Ozono, K.; Konno, K.; Fujishima, T.;
Takayama, H.; Okano, T. Biochem. Pharmcol. 2000, 59, 691-702.
(6) Suhara, Y.; Nihei, K.; Tanigawa, H.; Fujishima, T.; Konno, K.;
Nakagawa, K.; Okano, T.; Takayama, H. Bioorg. Med. Chem. Lett. 2000,
10, 1129-1132.
a Conditions and yields: (a) HOCH2(CH2)nCH2OH, KOtBu, 110
°C, 14 h, n ) 0 (88%), n ) 1 (94%), and n ) 2 (93%); (b)
TBDMSCl, imidazole, DMF, n ) 0 (93%), n ) 1 (92%), and n )
2 (99%); (c) NBS, BaCO3, CCl4, reflux, 35 min, n ) 0 (71%), n )
1 (74%), and n ) 2 (76%); (d) catalytic NaOMe, MeOH, n ) 0
(95%), n ) 1 (96%), and n ) 2 (99%); (e) TBDMSCl, imidazole,
DMF, n ) 0 (93%), n ) 1 (94%), and n ) 2 (85%); (f) catalytic
Bu4NF, THF, n ) 0 (43%), n ) 1 (71%), and n ) 2 (68%); (g)
Zn, NaBH3CN, 1-propanol-H2O (10:1), 95 °C, 45 min, and then,
NaBH4, n ) 0 (71%), n ) 1 (72%), and n ) 2 (75%); (h) TmCl,
DMAP, CH2Cl2, n ) 0 (82%), n ) 1 (84%), and n ) 2 (92%); (i)
LiHMDS, THF, -78 °C to rt, n ) 0 (92%), n ) 1 (99%), and n )
2 (90%); (j) TMSCCH, BuLi, BF3OEt2, THF, -78 °C, n ) 0 (91%),
n ) 1 (92%), and n ) 2 (94%); (k) K2CO3, MeOH, n ) 0 (93%),
n ) 1 (96%), and n ) 2 (63%); (l) TBDMSOTf, 2,6-lutidine,
CH2Cl2, 0 °C, n ) 0 (92%), n ) 1 (90%), and n ) 2 (80%).
(7) (a) Umesono, K.; Murakami, K. K.; Thompson, C. C.; Evans, R. M.
Cell 1991, 65, 1255-1266. (b) DeLuca, H. F.; Zierold, C. Nutr. ReV. 1998,
56, 54-75. (c) Takeyama, K.; Masuhiro, Y.; Fuse, H.; Endoh, H.;
Murayama, A.; Kitanaka, S.; Suzawa, M.; Yanagisawa, J.; Kato, S. Mol.
Cell. Biol. 1999, 19, 1049-1055. (d) Yanagisawa, J.; Yanagi, Y.; Masuhiro,
Y.; Suzawa, M.; Watanabe, M.; Kashiwagi, K.; Toriyabe T.; Kawabata,
M.; Miyazono, K.; Kato, S. Science 1999, 283, 1317-1321.
2620
Org. Lett., Vol. 2, No. 17, 2000

protection of the primary alcohol, treatment of benzylidene
acetal 6 with NBS10 gave bromide 7 in 74% yield. Exchange
of the protecting group on the C4 hydroxyl group was
accomplished through mild solvolysis of the benzoate,
persilylation, and selective deprotection of the C2 hydroxyl
group to obtain bis-O-silylated 10 in good yield.11 Reaction
of bromide 10 with activated zinc powder generated an
aldehyde, which was directly reduced to alcohol 11.9,12
Sulfonylation of the primary alcohol and LiHMDS treatment
afforded epoxide 13, into which was subsequently introduced
the acetylene unit with ring opening. Removal of the terminal
TMS group under basic conditions and the protection of the
secondary alcohol with TBDMS provided 1,7-enyne 16 (n
) 1) in high yield (Scheme 1), which is suitable for the
following Trost-Dumas palladium-catalyzed coupling reac-
tion.13 The other A-ring precursors (16) were also prepared
by a similar procedure using ethylene glycol (n ) 0) and
1,4-butanediol (n ) 2) instead of 1,3-propanediol.
Table 1. Relative Binding Affinity of the Series of 1 for
Bovine Thymus 1R,25-Dihydroxyvitamin D3 Receptor (VDR)
compounds
VDRa
1R,25(OH)2D3
1a (n ) 0)
1b (n ) 1)
1c (n ) 2)
100
120
180
40
a The potency of 1R,25(OH)2D3 is normalized to 100.
and Arg-274. The potent VDR affinity of 1a and 1b could
be explained by molecular mechanics calculations based on
the crystal structure established by Moras et al.15a In a
preliminary calculation,16 the C2R terminal hydroxyl group
of 1b is likely to reach toward not only Asp-144 but also
Tyr-236 to create additional hydrogen bond networks. On
the other hand, the C2R terminal hydroxyl group of 1a
probably forms a hydrogen bond with Arg-274. Formation
of the new hydrogen bonds could be one of the reasons for
the high affinity. Furthermore, based on the calculation, the
2R-substituted A-ring, except for the 2R-methyl case, fits
into the cavity in the R-conformation to minimize steric
repulsion. In this conformation, the 2R-substituent adopts
the equatorial position and the 1R-hydroxyl group retains
hydrogen bonding with Ser-237 (Figure 2). Very recently,
Palladium-mediated alkylative cyclization with vinyl bro-
mide of the CD fragment 1713 from Grundmann’s ketone
and subsequent deprotection furnished the target 2R-
substituted 1R,25-dihydroxyvitamin D3 derivatives 1 in
considerable yields (Scheme 2).
Scheme 2a
a Conditions and yields: (a) catalytic (Ph3P)4Pd, Et3N-toluene
(1:1), reflux, n ) 0 (75%), n ) 1 (52%), and n ) 2 (69%); (b)
Bu4NF, THF, n ) 0 (78%), n ) 1 (61%), and n ) 2 (70%).
Figure 2. Computer calculation of 1b in the VDR ligand binding
domain.
we reported that 2R-(3-hydroxypropyl)-1R,25(OH)2D3 (3)
The receptor binding potency of 1a-c was evaluated using
bovine thymus VDR,14 and the results are summarized in
Table 1. Interestingly, the highest binding affinity of this
series occurred with 1b (n ) 1), which is 1.8 times higher
than that of 1R,25(OH)2D3.
Recently, studies on the three-dimensional structural
elucidation of the 1R,25(OH)2D3 docking VDR ligand
binding domain have been carried out.15 It is noteworthy that
there is a rather hydrophobic cavity around the C2 position
surrounded by Phe-150, Tyr-143, Tyr-147, and Tyr-236.
Interestingly, Asp-144 is found at the end of this long cavity.
The 1R-hydroxyl group forms hydrogen bonds with Ser-237
showed a 3-fold increase in binding activity to VDR.6 The
(8) Wiggins, L. S. Methods Carbohydr. Chem. 1963, 2, 188-191.
(9) Beau, J.-M.; Aburaki, S.; Pougny, J.-R.; Sinay, P. J. Am. Chem. Soc.
1983, 105, 621-622.
(10) (a) Hanessian, S. Methods Carbohydr. Chem. 1972, 6, 183-189.
(b) Hanessian, S.; Plessas, N. R. J. Org. Chem. 1969, 34, 1035-1044.
(11) In the case of n ) 1, recovered 9 (23%) and a mixture of diols
(15%), which could be quantitatively recycled to the tris-O-TBDMS
derivative 9, were obtained. Then, the recovered 9 and the recycled 9 were
combined and desilylated again. Overall yield of 10 for these three steps
was 72%. For n ) 0 and 2, this recycled step was also applied and overall
yields were noted in Scheme 1.
(12) (a) Bernotas, R. C.; Pezzone, M. A.; Ganem, B. Carbohydr. Res.
1987, 167, 305-311. (b) Bernet, B.; Vasella, A. HelV. Chim. Acta 1979,
62, 1990-2016.
Org. Lett., Vol. 2, No. 17, 2000
2621

distance between the C2-atom and the terminal hydroxyl
group of 3 is almost the same as that for compound 1a. It is
conceivable that different binding activities of these ana-
logues could be due to matching of the hydrophobicity just
around the C2 position.
Acknowledgment. The authors thank Misses J. Shimode
and M. Kitsukawa (Teikyo University) for spectroscopic
measurements. This work has been supported in part by a
Grant-in-Aid from the Ministry of Education, Science, Sports
and Culture of Japan.
In conclusion, we have developed an efficient synthetic
route to the new biologically active 2R-(ω-hydroxyalkoxy)-
1R,25(OH)2D3 (1a-c) through the new A-ring synthon,
enyne 16, from R-D-glucose. It was found that VDR binding
affinity of 1b is 1.8 times higher than that of the native
hormone. This increased affinity was elucidated by molecular
mechanics calculations based on the crystal structure of VDR
bound to its natural ligand. We believe this synthetic strategy
could be applicable to a wide range of novel 2R-substituted
1R,25(OH)2D3 derivatives by simply using various nucleo-
philes toward epoxide 4. Further synthetic and biological
studies in this area are currently in progress in our laboratory.
Supporting Information Available: Experimental detail
and characterization data for compounds 1a-c and 5-10
(represented by n ) 1) and charts of VDR binding assays
for 1a-c. This material is available free of charge via the
Internet at http://pubs.acs.org.
OL006222J
(15) (a) Rochel, N.; Wultz, J. M.; Mitschler, A.; Klaholz, B.; Moras, D.
Mol. Cell 2000, 5, 173-179. (b) Yamamoto, K.; Masuno, H.; Choi, M.;
Nakashima, K.; Taga, T.; Ooizumi, H.; Umesono, K.; Sicinska, W.;
VanHooke, J.; DeLuca, H. F.; Yamada, S. PNAS 2000, 97, 1467-1472.
(c) Norman, A. W.; Adams, D.; Collins, E. D.; Okamura, W. H.; Fletterick,
R. J. J. Cell. Biochem. 1999, 74, 323-333.
(16) Calculated by MacroModel ver. 6.5 (Schrodinger, Inc.) on a SGI
O2 Workstation. The C17 steroidal side chain was omitted for the
calculation.
(13) Trost, B. M.; Dumas, J.; Villa, M. J. Am. Chem. Soc. 1992, 114,
9836-9845.
(14) Imae, Y.; Manaka, A.; Yoshida, N.; Ishimi, Y.; Shinki, T.; Abe,
E.; Suda, T.; Konno, K.; Takayama, H.; Yamada, S. Biochim. Biophys.
Acta 1994, 1213, 302-308.
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