Vitamin D3: Synthesis of seco-C-9,11-bisnor-17-methyl-1α,25-dihydroxyvitamin D3 analogues

Article abstract of DOI:10.1016/S0960-894X(02)00222-6

The synthesis and biological properties of seco-C-9,11-bisnor-17-methyl-1α,25-dihydroxyvitamin D₃ novel D-ring analogues are described.

Full text of DOI:10.1016/S0960-894X(02)00222-6

Bioorganic & Medicinal ChemistryLetters 12 (2002) 1633–1636
Vitamin D3: Synthesis of seco-C-9,11-bisnor-17-Methyl-1ꢀ,
25-dihydroxyvitamin D3 Analogues
Yusheng Wu,a Pierre De Clercq,a Maurits Vandewalle,a,* Roger Bouillonb
and Annemieke Verstuyf b
aGhent University, Department of Organic Chemistry, Laboratory for Organic Synthesis, Krijgslaan 281 S4, B-9000 Gent, Belgium
bLaboratorium voor Experimentele Geneeskunde en Endocrinologie, K.U. Leuven, Onderwijs en Navorsing Gasthuisberg,
Herestraat 49, B-3030 Leuven, Belgium
Received 14 January2002; accepted 3 April 2002
Abstract—The synthesis and biological properties of seco-C-9,11-bisnor-17-methyl-1a,25-dihydroxyvitamin D3 novel D-ring ana-
logues are described. # 2002 Elsevier Science Ltd. All rights reserved.
The observation that 1a,25-dihydroxyvitamin D3 (1,
calcitriol) is active in the regulation of cell proliferation
and differentiation, next to the classical role in calcium-
bone homeostasis, has led in recent years to the devel-
opment of analogues capable of dissociating cell
differentiating effects from calcemic effects (Fig. 1).1ꢀ3
In the context of a long-standing study4 of analogues
modified in the central part (C-8–C-20) we presently
describe the synthesis of new 17-methyl ‘D-ring’ ana-
logues, lacking the six-membered C-ring, 3 (natural
A-ring) and 4 (19-nor compounds). The geminal di-
methyl group at C-13 (steroid numbering) mimics C-12
and C-18, in 1 and 2 which are known to influence side
chain orientations.3 As this also holds for the C-20
configuration we plan to produce both the R (natural)
and S epimers. It is indeed generallyassumed that the
relative position in space of the 1a- and 25-hydroxy
groups is important for the biological activityand that
the side chain occupies a veryrestricted topologyat the
binding site of the vitamin D receptor (VDR).3,5
Analogues 3 and 4 will be constructed via the Lythgoe
coupling6 of an appropriate 8-formyl-D-ring fragment 5
(from 1S,3R-camphoric acid 7) with respectively
phosphine oxides 6a8 and 6b.7a
In the preceding paper,9 we described the synthesis of
the related 21-nor-17-methyl D-ring analogues via the
unsaturated ester 8 which was found to be also a valu-
able precursor for the present target molecules (Scheme 1).
Several approaches for the introduction of the required
21-methyl group, for example conjugate addition to 8 or
substitution of tosylate 23b (Scheme 2), failed due to the
highlyhindered position of C-20.
Figure 1.
A viable rou0te was then found, involving a copper
mediated SN2 reaction10 on allylic bromide 10 obtained
from 8 (Scheme 1).
*Corresponding author. Tel.: +32-9-264-4460; fax: +32-9-264-4998;
e-mail: pierre.declercq@rug.ac.be
0960-894X/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(02)00222-6

1634
Y. Wu et al. / Bioorg. Med. Chem. Lett. 12 (2002) 1633–1636
The reaction was completelydiastereoselective and led
to 11 with unnatural 20(S) configuration. This is in
accordance with the Felkin rule11 and with Corey’s
basis of Felkin’s model — expected 20(R). Structure 19
was established byNOE, COSY, 1H and 13C NMR
experiments. Lactone 19 is the thermodynamically most
stable epimer as in 20 there is severe sterical hindrance due
to the 1,3-diaxial interaction between C-18 and C-21. That,
indeed acid catalyzed epimerization had occurred during
the lactonisation was shown byreduction of 18 and 19
which respectivelyled to the two epimeric diols 21 and 22.
0
model12 of d–p* complexation in SN2 reactions.
Chemical proof followed from routine transformation
of 11 into the rigid lactone 19 (Scheme 2). Lactonisation
of intermediate 18 led to 19(S) instead of the — on the
Scheme 1. (a) See ref 8; (b) DIBALH, CH2Cl2, ꢀ78!50 ꢁC, 2.5 h; (c) CBr4, Ph3P, CH2Cl2, ꢀ60!35 ꢁC, 2 h; (d) CuBrMe2S, MeLi, ZnCl2, THF,
ꢁ
ꢁ
ꢁ
ꢁ
.
ꢀ78!ꢀ50 C, 4.5 h, then 9, ꢀ78!rt, 5.5 h; (e) 9-BBN, THF, 50 C, 3.5 h, then 30% H2O2, 50 C, 1 h; (f) Py SO3, DMSO–CH2Cl2, ꢀ20!15 C,
1.5 h, (g) (MeO)2P(O)CHN2, t-BuOK, THF, ꢀ78 ꢁC, 40 min, 11, ꢀ78!rt; (h) LDA, HMPA, THF, ꢀ20 ꢁC, then R2CO, ꢀ30!5 ꢁC, 2–3 h; (i) TBAF,
THF, rt; (j) (COCl)2, DMSO, CH2Cl2, ꢀ78 ꢁC, then Et3N, ꢀ78!ꢀ10 ꢁC, 2–3 h; (k) 5%, Rh/Al2O3, 1 atm H2, EtOAc, rt 8 h.
Scheme 2. (a) TBAF, THF, rt, 4 h; (b) (COCl2), DMSO, ꢀ78 ꢁC, then Et3N, ꢀ78!ꢀ10 ꢁC, 3 h; (c) (i) MeMgBr, THF, 20 ꢁC, 2 h, (ii) PDC, CH2Cl2,
rt, 12 h; (d) O3, NaOH, MeOH–CH2Cl2, ꢀ78 ꢁC, 3 h; (e) m-CPBA, CHCl3, rt 3 days; (f) LiOH, THF–MeOH, rt, overnight; (g) TsOH, CH2Cl2, rt,
12 h, (h): DIBALH, CH2Cl2, ꢀ78!ꢀ40 ꢁC, 3 h; (i) O3, hexane–CH2Cl2–MeOH, py, ꢀ78 ꢁC, 2 h, then, NaBH4, ꢀ78!20 ꢁC, 4 h; (j) DBU, CH2Cl2,
ꢁ
.
rt, 12 h, 45–49% conversion; (k) (i) MeOCH2PPh3 Cl, LDA, THF–HMPA (5:2), ꢀ20!0 C, 1 h, then 25, ꢀ40!rt, 2.5 h; (l) Hg(OAc)2, THF, rt, 1 h,
then 7% KI, (m) (MeO)2P(O)CHN2 t-BuOK, THF, ꢀ78 ꢁC, 1 h, 27, ꢀ75 ꢁC, !rt, 16 h; (n) LDA, HMPA, THF, ꢀ20 ꢁC, then R2CO, ꢀ30!5 ꢁC,
2!3 h; (o) TBAF, THF, rt; (p) (COCl)2, DMSO, CH2Cl2, ꢀ78 ꢁC, then Et3N, ꢀ78!ꢀ10 ꢁC, 2–3 h; (q) 5%, Rh/Al2O3, 1 atm H2, EtOAc, rt 8 h.

Y. Wu et al. / Bioorg. Med. Chem. Lett. 12 (2002) 1633–1636
1635
Transformation of 11 into the C-8 formyl precursors 15
and 16 is straightforward; hydroboration and oxidation
gave 12, which upon Seyferth’s13 reaction led to alkyne
13. Reaction of lithiated 13 with a series of ketones gave
14a,b,c which were then transformed into 14a,b,c (two
steps) and 16a,b,c (three steps).
tection afforded the title compounds 3 and 4 (Scheme 3)
with six different side chains each with respectivelythe
20-(R) and -(S) configuration (see Table 1).
The affinityto the pig intestinal mucosa vitamin D
receptor (VDR) was evaluated as described pre-
viously.14 The relative affinityof the analogues was cal-
culated from their concentration needed to displace
50% of [3H] 1a,25(OH)2D3 from its receptor compared
with the activityof 1 (assigned a value of 100%). The in
vivo calcemic effects were tested in vitamin D-replete
normal NMRI mice bydailyintraperitoneal injections
of 1a,25(OH)2D3, its analogues or the solvent during 7
consecutive days, using serum calcium concentration as
parameter.
For the synthesis of analogues with the natural 20(R)
configuration (Scheme 2) we planned to equilibrate
aldehyde 24 to epimer 25. Therefore 11 was transformed
in two steps to 24. Base catalyzed equilibration gave a
1:1 ratio of 24 and 25 which could be separated bypre-
parative HPLC. Homologation (1C) of 25 led, via 26, to
27, the C-20 epimer of 12. Subsequent synthesis of pre-
cursors 29a,b,c and 30a,b,c was carried out in essentially
the same yields as described for 14a,b,c or 15a,b,c (see
Scheme 1) from 2.
The biological evaluation was determined in vitro on
different cell lines (HL 60, MCF-7, keratinocytes). All
results are the mean of at least three experiments and
are expressed as percentage activity(at 50% dose
response) in comparison with 1a,25(OH)2D3 (=100%
activity). The affinity of the D-ring analogues for VDR
varied between 30 and 80% compared to 1 (Table 1).
6
FinallyLythgoe coupling of the 8-formyl precursors
with phosphine oxide 6a or 6b and subsequent depro-
The antiproliferative (MCF-7, keratinocytes) activities
are high, especiallyfor the hexafluoro analogues; as a
general observation it appears that, within a pair of 20-
epimers, the S-epimer is the more potent. Several ana-
logues displayhigh ratios of differentiation between
antiproliferative and calcemic effects. The anti-
proliferative activities of WY 1112 and WY 1113 are
comparable with the in vitro activityof known ‘top’
analogues such as 20-epi-22-oxa-24,26–27-trihomo-
1a,25(OH)2D3 (KH 1060)15 or 20-epi-22-ethoxy-23-yne-
24,26,27-trihomo-1a,25(OH)2D3 (CB 1093).16
Scheme 3. (a) BuLi, THF, ꢀ78 ꢁC!ꢀ20 ꢁC, 3 h; (b) TBAF, THF, rt,
12 h.
Table 1. Biological activities
Side chain
Code
C-20
A-ring
VDR
HL-60
MCF-7
Keratinocytes
Calcium serum
1
R
S
R
S
3
3
3
4
4
100
85
6
40
3
100
800
50
600
10
100
2000
60
400
8
100
1000
100
600
80
100
8
0.25
0.5
0.12
WY 821
WY 1036
WY 1116
WY 1037
R
WY 826
WY 1018
WY 1117
WY 1019
S
R
S
3
3
4
4
85
50
60
10
1250
150
500
80
15,000
300
7500
150
7000
400
7000
300
100
2
20
0.5
R
WY 1112
WY 1038
WY 1113
WY 1039
S
R
S
3
3
4
4
60
30
40
9
400
150
400
100
30,000
2500
20,000
600
20,000
2400
16,000
1500
>100
10
100
50
R
WY 9361
WY10061
WY 1106
WY 1046
S
R
S
3
3
4
4
75
60
40
7
800
80
350
85
1250
600
1300
70
3250
500
2000
200
3
3
4
0.12
R
WY 9371
WY 10051
WY 1107
WY 1047
S
R
S
3
3
4
4
80
80
60
50
600
75
400
50
750
150
700
85
800
80
300
85
25
2
2
0.25
R
WY 939
WY 10071
WY 1108
WY 1048
S
R
S
3
3
4
4
75
60
50
50
1250
250
400
300
8000
4500
6000
1500
15,000
3600
15,000
3000
25
6
25
3
R

1636
Y. Wu et al. / Bioorg. Med. Chem. Lett. 12 (2002) 1633–1636
Further details of the biological activities and considera-
tions obtained from comparison with other D-ring
analogues will be published elsewhere.
weyn, C.; Van Haver, D.; Zhu, G.-D.; Chen, Y.-J.; Zhou, X.;
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Acknowledgements
We thank the ‘FWO’, the ‘Ministerie voor Wetenschaps-
beleid’ and THERAMEX S.A. for financial support.
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