Synthesis and biological activity of the 1α,25-dihydroxyvitamin D3 diastereomer with unnatural configuration at the rings C/D side-chain moiety

Article abstract of DOI:10.1016/S0960-894X(00)00598-9

1α,25-Dihydroxyvitamin D₃ diastereomer, differing from the parent compound in configuration at four asymmetric carbon atoms in the rings C/D and side chain (C13, C14, C17 and C20), was synthesized and shown to have a significant affinity for the vitamin D receptor. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0960-894X(00)00598-9

Bioorganic & Medicinal Chemistry Letters 11 (2001) 63±66
Synthesis and Biological Activity of the 1ꢀ,25-Dihydroxyvitamin
D3 Diastereomer with Unnatural Con®guration at the
Rings C/D Side-Chain Moiety
Stanis•aw Marczak,a Agnieszka Przezdziecka,a Jerzy Wicha,a,*
Andreas Steinmeyerb and Ulrich Zugelb
aInstitute of Organic Chemistry, Polish Academy of Sciences, POB 58, 01-224 Warsaw 42, Poland
bSchering AG, Preclinical Drug Research, D-13342 Berlin, Germany
Received 6 September 2000; accepted 20 October 2000
AbstractÐ1a,25-Dihydroxyvitamin D3 diastereomer, di€ering from the parent compound in con®guration at four asymmetric
carbon atoms in the rings C/D and side chain (C13, C14, C17 and C20), was synthesized and shown to have a signi®cant anity for
the vitamin D receptor. # 2000 Elsevier Science Ltd. All rights reserved.
1a,25-Dihydroxyvitamin D3 (1, Scheme 1), the major
active metabolite of vitamin D3, exerts hormonal con-
trol over important physiological processes, including
calcium and phosphorus metabolism, cellular di€er-
entiation and immune reactions.1 A great deal of atten-
tion has been devoted to synthesis of analogues of this
natural compound that would discriminate certain types
of its activity.2 One of the interesting lines of the struc-
ture±activity studies is concerned with stereoisomers of
compound 1. Epimers of 1 di€ering in con®guration at
one of the stereogenic centres, Cl, C3, C14 or C20, have
been studied.3 These studies have shown, among other
important results, that the 1a,25-dihydroxyvitamin D3
epimer 2 di€ering in con®guration at C20 and, in con-
sequence, in the side-chain orientation, exhibits high
anity to the vitamin D receptor and enhanced cell-
di€erentiation activity.3d The activity of the 20-iso-epi-
mer posed a question of the importance of the natural
con®guration at all remaining stereogenic centres in the
northern, `terpenoid' portion of 1a,25-dihydroxy
vitamin D3 for its recognition by the receptor.
side-chain building block 14 of the target compound 3 is
illustrated in Scheme 2. Asymmetric Robinson annula-
tion5 of 2-methylcyclopentan-1,3-dione 5 with (phe-
nylsulfanyl)methyl vinyl ketone
4 using (R)(+)-
phenylalanine as the catalyst was carried out according
to the procedure of Hagiwara and Uda,6 involving a
gradual increase of the reaction temperature, to a€ord
dione 6 with 89% ee in 71% yield. Dione 6 was reduced7
into trans-hydrindane derivative 7 and the latter was
transformed in the usual way into ester 8. Alkylation8 of
8 by means of LDA (2 equiv) and bromide 9 (prepared
from a-acetyl-ꢀ-butyrlactone via 1-bromopent-4-one9 in
30% overall yield) gave compound 10 contaminated
with a byproduct which could not be separated by
chromatography. Under optimized conditions with the
use of 1.5 equivalent of LDA the alkylation products
were obtained with 76% yield in an estimated ratio of
95:5 (by 1H NMR). Reduction of the alkylation product
with DIBAL a€orded a mixture of alcohols which were
separated by chromatography. The major product, iso-
lated in 85% yield, was identi®ed as 12. To the side-
product structure, 13 was assigned on the grounds of its
spectral and analytical properties. Formation of 13
indicated that under conditions of alkylation of 8 along
with ester enolate, some a-sulfonyl anion was generated
which resulted in the side product 11. Further reduction
of alcohol 12 provided the required building block 14.
In order to evaluate the e€ect of con®gurational chan-
ges on activity of vitamin D analogues we conducted
synthesis and biological evaluation of compound 3
which combines `natural' ring A and C/D rings side-
chain portion with inverted con®guration at all asym-
metric carbon atoms.4 Our synthesis of the C/D rings
A common ring A precursor 15 was oxidized with Dess±
Martin reagent10 to give a mixture of aldehyde 16 and
its tautomer with pyrane ring11 17 in a ratio of ca. 2:1,
*Corresponding author. Tel.: +48-22-632-8117; fax: +48-22-632-
6681; e-mail: jwicha@icho.edu.pl
0960-894X/01/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(00)00598-9

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S. Marczak et al. / Bioorg. Med. Chem. Lett. 11 (2001) 63±66
by 1H NMR. The mixture was puri®ed by ®ltration
through a silica gel column, dried and used immediately
for the next reaction (Scheme 3).
®rst with butyllithium to generate a-sulfonyl anion and
then, at 78 ꢀC, with a mixture of aldehyde and its
tautomer 16±17 (0.5 equiv). After 1 h, an excess of
freshly distilled acetyl chloride was added and the mix-
ture was stirred at room temperature for 15 h. A mix-
ture of acetoxy sulfones 18a and 18b was obtained. The
mixture was submitted to reduction with 6% sodium
amalgam without puri®cation. The resulting product
was ®ltered through a silica gel column to give a mixture
of silyloxy and acetoxy trienes 19a and 19b in 45% yield
For coupling of the building blocks a modi®ed
Kocienski procedure12 for executing the Julia ole®na-
tion reaction13 in vitamin D synthesis was used. It
should be noted that the Julia±Kocienski method has
never been used for the preparation of 1a,25-dihydroxy-
vitamin D3 derivatives. Sulfone 14 (1 equiv) was treated
Scheme 1. Structure of 1a,25-dihydroxyvitamin D3 (1) and its analogues di€ering in con®guration of stereogenic centres in C/D rings side-chain
portion.
Scheme 2. Synthesis of the C/D rings side-chain building block: (a) (R)-(+)-phenylalanine, DMF/Et3N/D-CSA, 25!55 ꢀC, 71%, 89% ee;
(b) m-CPBA, CH2Cl2; (c) LiAlH4, THF, re¯ux; (d) Jones reagent, acetone, 77% overall from 6; (e) NaH, (EtO)2P(O)CH2CO2Et, DMF/HMPA,
20!25 ꢀC, 80%; (f) H2/Pd, EtOH, 97%; (g) LDA, THF/HMPA, then 9 78!25 ꢀC, 76%; (h) DIBAL-H, CH2Cl2, 20!25 ꢀC, 85% of 12 and
4% of 13; (i) MsCl, CH2Cl2, 20 ꢀC; (j) LiEt3BH, THF, 84% overall from 12.

S. Marczak et al. / Bioorg. Med. Chem. Lett. 11 (2001) 63±66
65
Scheme 3. Preparation of the ring A building block and the coupling reaction. (a) Dess±Martin reagent, CH2Cl2, 90%; (b) n-BuLi, THF, then 16
and 17 and after 1 h AcCl, 78!25 ꢀC; (c) Na±Hg, MeOH/Na2HPO4, 20 ꢀC, 45% overall from 12; (d) TBAF/4 A MS, THF, 80%.
Acknowledgements
from 15 (ratio 60:40, respectively, by NMR). These
experiments show that under the conditions of ole®na-
tion simultaneously with acetylation of the very steri-
cally hindered hydroxy group at C7, partial exchange of
the protective triethylsilyl group for the acyl group at
the C25 has also occurred. The mixture 19 was next
Financial support from the Polish State Committee for
Scienti®c Research is acknowledged (Grant No. 3 T09A
134 18).
.
treated with TBAF H2O and 4 A molecular sieves in
THF and the products were separated by ¯ash chroma-
tography to give triol 3 (27% yield from 16±17) and its
C25-acetate (8.4% yield). HPLC analysis of thus pre-
pared vitamin D analogue 3 (Nucleosil, EtOAc±
CH2C12, 1:1) indicated its contamination with small
amounts of double bond isomers.14 Finally, a sample of
3 was puri®ed by HPLC and its structure was con®rmed
by spectroscopic measurements (MS, UV, 1H NMR,
CD).
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