Studies on the introduction of a photoreactive aryldiazirine group into the vitamin D skeleton

Article abstract of DOI:10.1002/1099-0690(200208)2002:15<2529::AID-EJOC2529>3.0.CO;2-2

The synthesis of a vitamin D analog with a diazirinyl benzylidene fragment replacing the side chain shows that diazirinylarylation of the upper vitamin D unit does not prevent the use of the convergent Lythgoe-Hoffman La Roche route to photoreactive analogs of potential value for photoaffinity labeling. The key step towards the diazirinylarylated upper fragment is the simultaneous oxidation of the hydroxyl and diaziridinyl groups of intermediate 10. Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.

Full text of DOI:10.1002/1099-0690(200208)2002:15<2529::AID-EJOC2529>3.0.CO;2-2

FULL PAPER
Studies on the Introduction of a Photoreactive Aryldiazirine Group into the
Vitamin D Skeleton[‡]
[a]
[a]
´
˜
Ana Fernandez-Gacio and Antonio Mourino
Dedicated to the memory of Prof. Angel Alberola
Keywords: Vitamins / Receptors / Proteins / Photoaffinity labeling
The synthesis of a vitamin D analog with a diazirinyl benzyli-
dene fragment replacing the side chain shows that diazirinyl-
arylation of the upper vitamin D unit does not prevent the
use of the convergent Lythgoe−Hoffman La Roche route to
photoreactive analogs of potential value for photoaffinity la-
beling. The key step towards the diazirinylarylated upper
fragment is the simultaneous oxidation of the hydroxyl and
diaziridinyl groups of intermediate 10.
( Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany,
2002)
Introduction
of VDR and DBP have been studied by means of site-spe-
cific mutations,[6] affinity-photoaffinity labeling,[7] fluores-
cence measurements,[8] X-ray diffractometry,[9] and
modeling.[9b,9c,10]
Therapeutic interest in calcitriol (1a, 1α,25-dihydroxy-
vitamin D3; Figure 1), which is the hormonally active form
of vitamin D3, and in some of its analogs, arises from their
ability to control abnormal cellular processes by modula-
ting cell differentiation, inhibiting cell proliferation and
regulating apoptosis.[2] Several of these compounds, includ-
ing calcitriol itself, are already marketed or are undergoing
clinical trials for the treatment of skin disease and can-
cer.[2f,2g] Research is currently focused on the development
of calcitriol analogs that have high antiproliferative activity
against a broad spectrum of cancer cells while lacking signi-
ficant calcemic effects.[2] The rational design of such ana-
logs depends on a detailed knowledge of the mode of action
of the parent hormone in its multiple physiological roles,
including anti-cancer and immunoregulatory effects.[3] Cur-
rently it is known that these activities involve specific bind-
ing of calcitriol to vitamin D receptor (VDR),[4] hetero-
dimerization of VDR with retinoid X receptor (RXR) and
binding of VDR-calcitriol-RXR complex to a vitamin D
response element (VDRE) in DNA, which is followed by
transcription of the associated gene.[2] An understanding of
the three-dimensional structures of VDR, vitamin D bind-
ing protein (DBP)[5] and the corresponding protein-ligand
complexes is of crucial importance for gaining new insights
into the mode of action of calcitriol. The tertiary structures
Figure 1. Structures of calcitriol (1a) and an aromatic side chain
analog (1b)
Photoaffinity labeling technique (PAL) has been used to
explore the ligand binding sites of a wide range of biomole-
cules, including steroids, peptide hormones and retinal. In
this technique, a photosensitive functional group is acti-
vated photochemically to generate highly reactive interme-
diates such as nitrenes or carbenes, which form stable cova-
lent bonds with proteins.[11] PAL studies of proteins related
to vitamin D have used the triene system[12] of calcitriol
itself and a 4-azido-2-nitro-phenyl moiety[7] attached to cal-
citriol through its 3-hydroxy group, but have not employed
the aryltrifluoromethyldiazirinyl system, which has been re-
ported to be superior in many cases to classical azido
probes.[11,13,14] This, and the fact that replacement of a frag-
ment of calcitriol by an aromatic ring can give rise to
[‡]
[a]
[1]
See Ref.
´
´
Departamento de Quımica Organica y Unidad Asociada al
CSIC, Universidad de Santiago de Compostela,
15706 Santiago de Compostela, Spain
E-mail: qomourin@usc.es
Supporting information for this article is available on the
WWW under http://www.eurjoc.org or from the author.
Eur. J. Org. Chem. 2002, 2529Ϫ2534  WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002 1434Ϫ193X/02/0815Ϫ2529 $ 20.00ϩ.50/0
2529

´
A. Fernandez-Gacio, A. Mourin˜o
FULL PAPER
vitamin D analogs that bind significantly to VDR and/or
have differentiation-promoting or antiproliferative effects,
but with reduced calcemic activity,[15] has led us to consider
the use of aryldiazirinyl units to prepare calcitriol-like PAL
reagents. We describe here the synthesis of the first such
vitamin D arylaziridine analog 2, in which the side chain of
the aromatic ring of analog 1b (Scheme 1) has been replaced
by a trifluoromethyldiazirinyl fragment. Compound 2 was
chosen as our target because 1b stimulates cell differenti-
ation to the same degree as calcitriol itself, but with less
calcemic effects.[16]
Scheme 2. a: Diethyl (3-bromobenzyl)phosphonate, KH, THF, ∆
(69%); b: nBuLi, THF, CF3COOMe (86%); c: hν, THF (75%); d:
H2NOH·HCl, py, EtOH, ∆ (90%); e: p-TsCl, Et3N, DMAP,
CH2Cl2 (91%)
Scheme 1. Retrosynthesis of the diazirinylarylated vitamin D ana-
log 2
mate (PDC) resulted in the oxidation of both the hydroxyl
and diaziridine groups, giving the desired diazirine 3 in
87% yield.[21]
Results and Discussion
Our plan for the synthesis of vitamin D analog 2 was to
use the convergent LythgoeϪHoffman La Roche approach
to the vitamin D triene system.[2a,2c] Key elements of the
synthesis include the formation of the diazirine-bearing
fragment 3 and its coupling with the lithium anion of phos-
phane oxide 4 (Scheme 1). The first of these stages began
with the preparation of O-tosyloxime 9 from ketone 5[17]
(Scheme 2).
Ketone 5 was converted, as previously described,[16] to an
approximately 4:1 mixture of bromide 6 and its Z diastereo-
isomer. Lithiation of these bromides (nBuLi, THF), fol-
lowed by treatment with methyl trifluoroacetate, led to an
86% yield of trifluoroketones 7 in the same isomer ratio.
Irradiation of a solution of this mixture in THF (450 W,
Hanovia medium pressure-Hg lamp, Pyrex, 90 min)
inverted the isomer ratio, giving an approximately 4:1 ratio
of 8 and 7, the stereochemistry of which was established by
1H NMR NOE experiments and by comparison of their
1H NMR spectra with those of similar compounds.[18] O-
tosyloxime 9 was formed by treatment of 8 with hy-
droxylamine, followed by conventional tosylation of the re-
sulting oxime (82% from 8).[19]
Scheme 3. a: NH3, Et2O, Ϫ78 °C (99%); b: HF aq., CH3CN (99%);
c: PDC, CH2Cl2 (87%); d: 4, THF, nBuLi, Ϫ78 °C; then 3, Ϫ78 °C
to room temp. (97%); e: TBAF, THF (99%)
Scheme 3 shows the formation of the diazirine-bearing
upper fragment 3 and its coupling to vitamin D ring A in
the form of phosphane oxide 4. Reaction of O-tosyloxime
Finally, it was gratifying to observe that the diazirine ring
9 with liquid ammonia, followed by removal of the silyl survived the WittigϪHorner reaction used to introduce the
protecting group, produced the diaziridine 10 in excellent vitamin D triene system[13d,19] during the coupling of ke-
yield.[20] Treatment of alcohol 10 with pyridinium dichro- tone 3 to the anion of phosphane oxide 4.[22] Removal of
2530
Eur. J. Org. Chem. 2002, 2529Ϫ2534

Introduction of an Aryldiazirine Group into the Vitamin D Skeleton
FULL PAPER
1.27 (s, 3 H, Me-18 Z), 2.39 (m, 1 H, H-16 Z),2.48 (m, 1 H, H-16
E), 2.68 (m, 1 H, H-16 Z), 2.81 (m, 1 H, H-16 E), 4.06 (m, 1 H,
H-8 Z), 4.14 (m, 1 H, H-8 Z), 6.06 (s, 1 H, H-20 E), 6.19 (s, 1 H,
H-20 Z), 7.47 (t, J ϭ 7.7 Hz, 1 H, H-Ar),7.49 (m, 3 H, H-Ar), 7.64
(d, J ϭ 7.7 Hz, 1 H, H-Ar), 7.85 (d, J ϭ 7.8 Hz, 1 H, H-Ar),7.87
(s, 1 H, H-Ar), 8.02 (s, 1 H, H-Ar) ppm. 13C NMR (CDCl3,
62.83 MHz): δ ϭ Ϫ5.2 (CH3 Z), Ϫ5.2 (CH3 E), Ϫ4.9 (CH3 Z),
Ϫ4.9 (CH3 E), 17.5 (CH2 Z), 17.6 (CH2 E), 18.0 (C Z), 18.0 (C E),
20.6 (CH3 Z), 21.6 (CH3 E), 23.0 (CH2 Z), 24.1 (CH2 E), 25.8 (3
CH3 E/Z), 28.4 (CH2 E), 31.2 (CH2 Z), 34.2 (CH2 Z), 34.6 (CH2
the tert-butyldimethylsilyl (TBS) groups from the resulting
protected vitamin D compound with tetra-n-butylammo-
nium fluoride (TBAF),[23] gave the desired calcitriol analog
2 (96% yield from 3).
In summary, the first synthesis of a diazirine-bearing
photoactivable calcitriol analog has been achieved and
should be easily generalizable to related analogs. The syn-
thesis is concise (nine steps, 30% yield from ketone 5), and
starts from commercially available vitamin D2. Diazirinylar-
ylation of the upper vitamin D fragment does not prevent E), 36.8 (CH2 E), 37.4 (CH2 Z), 44.7 (C Z), 45.4 (C E), 50.5 (CH
E), 52.5 (CH Z), 69.2 (CH E), 69.7 (CH Z), 115.0 (CH E), 116.8
(CF3 E/Z, JC,F ϭ 291.6 Hz), 117.1 (CH Z), 126.9 (CH E), 127.6
(CH Z), 128.1 (CH Z), 128.8 (CH E), 129.2 (C Z), 129.5 (CH E),
129.9 (C E), 130.9 (CH Z), 135.0 (CH E), 136.4 (CH Z), 139.9 (C
E), 140.1 (C Z), 156.6 (C Z), 158.9 (C E), 180.6 (CϭO E/Z, q,
JC,F ϭ 34.8 Hz).
the use of the mild, convergent Lythgoe WittigϪHorner ap-
proach.
Experimental Section
General Methods. All reactions involving oxygen- or moisture-sen-
sitive compounds were carried out under a dry argon atmosphere.
Reaction temperatures refer to external bath temperatures. All dry
solvents were distilled under argon immediately prior to use. Tetra-
hydrofuran (THF) was distilled from Na/benzophenone; dichloro-
methane (CH2Cl2) was distilled from P2O5; absolute ethanol was
distilled from Mg/I2; pyridine was distilled from KOH and CaH2.
4-(Dimethylamine)pyridine (DMAP) was purchased from Aldrich
and used without further purification. Liquid reagents or solutions
of reagents were added by syringe or cannula. Photochemical reac-
tions were performed in a Pyrex glass reactor using a Hanovia lamp
(450 W) of medium mercury pressure. Organic extracts were dried
over anhydrous Na2SO4, filtered and concentrated using a rotary
evaporator at aspirator pressure (20Ϫ30 Torr). Reactions were
monitored by thin-layer chromatography (TLC) using aluminum-
backed Merck 60 silica gel plates (0.2 mm thickness); the chromato-
grams were visualized first with ultraviolet light (254 nm) and then
by immersion in a solution of phosphomolybdic acid in MeOH
(5%), followed by heating. Flash column chromatography was per-
formed with Merck 60 (230Ϫ400 mesh) silica gel. All NMR spectra
were measured with solutions in CDCl3 unless otherwise stated.
Chemical shifts are reported on the δ scale (ppm) downfield from
tetramethylsilane (δ ϭ 0.0 ppm) using the residual solvent signal at
δ ϭ 7.26 ppm (1H) or δ ϭ 77.0 ppm (13C) as internal standard;
coupling constants are reported in Hz. Distorsionless Enhance-
ment by Polarization Transfer (DEPT) was used to assign carbon
types. Mass spectra were obtained using electron-impact ionization
at 70 eV. Melting points were measured in open capillary tubes and
are uncorrected.
8β-tert-Butyldimethylsilyloxy-17(Z)-{1-[3-(2,2,2-trifluoroacetyl)-
phenyl]methylidene}de-A,B-androstane (8). A solution of 7 (200 mg,
0.442 mmol, 4:1 E:Z) in dry THF (30 mL) was irradiated for
90 min and then concentrated. The residue, which consisted of a
4:1 Z:E mixture, was purified by flash chromatography (1% EtOAc/
hexanes) to give 198 mg of 8 (99%). MS (FAB): m/z (%) ϭ 453 (20)
[MHϩ], 451 (40) [Mϩ Ϫ H], 395 (40) [Mϩ Ϫ C(CH3)3], 383 (100)
[Mϩ Ϫ CF3], 345 (37), 319 (95) [Mϩ Ϫ OTBS], 251 (87) [Mϩ
Ϫ
OTBS Ϫ CF3]. HRMS (calcd. for C25H36F3O2Si): 453.2437;
found 453.2439.
8β-tert-Butyldimethylsilyloxy-17(Z)-{1-[3-(2,2,2-trifluoro-1-
hydroxyiminoethyl)phenyl]methylidene}de-A,B-androstane
(pre-
cursor of 9): H2NOH·HCl (74 mg, 1.06 mmol) was added to a solu-
tion of 8 (319 mg, 0.71 mmol, Z:E:4:1) in dry pyridine (8 mL) and
dry EtOH (4 mL) and the resulting mixture was refluxed. After 4 h,
H2O was added and the aqueous layer was extracted with Et2O.
The combined organic fractions were washed with brine, dried, fil-
tered and concentrated in vacuo. The residue was purified by flash
chromatography (20% CH2Cl2/hexanes) to give 297 mg of the pre-
cursor of 9 [90%, Rf (Z) ϭ 0.35 (10% EtOAc/hexanes), 4:1 Z:E].
This oxime was purified by successive flash chromatography, taking
the head tubes at each stage. 1H NMR (CDCl3, 250 MHz): δ ϭ
Ϫ0.06 (s, 3 H, MeSi), Ϫ0.05 (s, 3 H, MeSi), 0.82 (s, 9 H, tBuSi),
1.17 (s, 3 H, Me-18), 2.58 (m, 1 H), 3.99 (m, 1 H, H-8), 6.12 (s, 1
H, H-20), 7.26 (m, 4 H, H-Ar), 8.92 (broad s, 1 H, H-Ar) ppm.
13C NMR (CDCl3, 62.83 MHz): δ ϭ Ϫ5.1 (CH3), Ϫ4.8 (CH3), 17.5
(CH2), 18.0 (C), 20.5 (CH3), 23.0 (CH2), 25.8 (3 CH3), 31.1 (CH2),
34.2 (CH2), 37.1 (CH2), 44.6 (C), 52.5 (CH), 69.7 (CH), 117.7
(CH), 120.6 (CF3, q, JC,F ϭ 274.9 Hz), 125.0 (C), 125.9 (CH), 127.6
8β-tert-Butyldimethylsilyloxy-17(E/Z)-{1-[3-(2,2,2-trifluoroacetyl)-
phenyl]methylidene}de-A,B-androstane (7): A solution of nBuLi
(2.35  in hexanes, 0.67 mL, 1.58 mmol) was added dropwise with
a syringe to a solution of bromide 6 (625 mg, 1.44 mmol; 1:4 E:Z
mixture) in dry THF (10 mL) at Ϫ78 °C. The resulting pale yellow
solution was stirred at Ϫ78 °C for 45 min. Freshly distilled
MeOC(O)CF3 (434 µL, 4.32 mmol) was then added slowly. The
solution was stirred at Ϫ78 °C for 1.5 h and then warmed to room
temp. over 40 min. The reaction was quenched with NH4Cl/H2O
(1:4). The mixture was extracted with EtOAc and the combined
organic phases were washed with brine, dried, filtered, and concen-
trated in vacuo. The residue was purified by flash chromatography
(100% hexanes) to give 558 mg of 7 [86%, Rf ϭ 0.63 (10% EtOAc/
(CH), 129.6 (CH), 131.4 (CH), 139.5 (C), 147.9 (C, q, JC,F
ϭ
32.3 Hz, C-CF3), 155.7 (C) ppm. MS: m/z (%) ϭ 467 (3) [Mϩ], 410
(13) [Mϩ Ϫ C(CH3)3], 335 (26) [Mϩ Ϫ OTBS], 75 (100). MS (FAB):
m/z (%) ϭ 468 (100) [MHϩ], 452 (85) [Mϩ Ϫ OH], 410 (20) [Mϩ
Ϫ
C(CH3)3], 336 (75) [Mϩ
Ϫ OTBS]. HRMS (calcd. for
C25H37F3NO2Si: 468.2546; found 468.2542.
8β-tert-Butyldimethylsilyloxy-17(Z)-{1-[3-(2,2,2-trifluoro-1-
tosyloxyiminoethyl) phenyl]methylidene}-de-A,B-androstane (9). Dry
Et3N (111 µL, 0.79 mmol) and DMAP (1.3 mg, 0.01 mmol) were
added to a solution of the previous oxime (247 mg, 0.53 mmol) in
dry CH2Cl2 (12 mL). The resulting solution was stirred at room
temp. for 45 min and then p-TsCl (152 mg, 0.79 mmol) was added.
hexanes), yellow oil]. The mixture of Z and E isomers was used After 16 h of stirring in the dark the reaction was quenched with
directly for the next reaction. 1H NMR (CDCl3, 250 MHz): δ ϭ
citric acid (0.2 ) and the aqueous phase was extracted with Et2O.
0.01 (s, 3 H, MeSi), 0.03 (s, 3 H, MeSi), 0.05 (s, 6 H, MeSi), 0.89
The combined organic fractions were washed with H2O, dried, fil-
(s, 9 H, tBuSi Z), 0.91 (s, 9 H, tBuSi E), 1.13 (s, 3 H, Me-18 E), tered and concentrated in vacuo. The residue was purified by flash
Eur. J. Org. Chem. 2002, 2529Ϫ2534 2531

´
A. Fernandez-Gacio, A. Mourin˜o
FULL PAPER
chromatography (10% CH2Cl2/hexanes) to give 300 mg of pure 9
250 MHz): δ ϭ 1.19 (s, 3 H, Me-18), 2.18 (d, J ϭ 8.69 Hz, 1 H,
NH), 2.30 (m, 1 H), 2.61 (m, 1 H), 2.72 (d, J ϭ 8.69 Hz, 1 H, NH),
[91%, Rf ϭ 0.45 (8% EtOAc/hexanes), colorless oil]. 1H NMR
(CDCl3, 250 MHz) [O-Ts (major)]: δ ϭ 0.00 (s, 3 H, MeSi), 0.01 (s, 4.04 (m, 1 H, H-8), 6.12 (s, 1 H, H-20), 7.23 (m, 4 H, H-Ar) ppm.
3 H, MeSi), 0.88 (s, 9 H, tBuSi), 1.20 (s, 3 H, Me-18), 2.34 (m, 1
H), 2.43 (s, 3 H, Ar-Me), 2.61 (m, 1 H), 4.04 (m, 1 H, H-8), 6.11
(s, 1 H, H-20), 7.28 (m, 6 H, H-Ar), 7.87 (d, J ϭ 8.3 Hz, 2 H, H-
13C NMR (CDCl3, 62.83 MHz): δ ϭ 17.2 (CH2), 20.2 (CH3), 22.5
(CH2), 30.9 (CH2), 33.5 (CH2), 37.2 (CH2), 44.2 (C), 52.1 (CH),
58.0 (C, q, C-CF3, J ϭ 35.8 Hz), 69.4 (CH), 118.2 (CH), 123.5 (C,
Ar) ppm. 13C NMR (CDCl3, 62.83 MHz) [O-Ts (major)]: δ ϭ Ϫ5.2 q, CF3, J ϭ 278.4 Hz), 125.5 (CH), 127.7 (CH), 127.8 (CH), 129.0
(CH3), Ϫ4.8 (CH3), 17.5 (CH2), 18.0 (C), 20.6 (CH3), 21.7 (CH3), (CH), 130.8 (C), 130.9 (CH), 131.0 (CH), 139.3 (C), 139.4 (C),
23.0 (CH2), 25.8 (3 CH3), 31.0 (CH2), 34.2 (CH2), 37.3 (CH2), 44.6
154.7 (C), 154.8 (C) ppm. MS: m/z (%) ϭ 353 (100) [MHϩ], 352
(C), 52.5 (CH), 69.6 (CH), 116.6 (CF3, JC,F ϭ 385.0 Hz), 117.3 (19) [Mϩ], 335 (72.5) [MHϩ Ϫ H2O], 147 (81). MS (FAB): m/z
(CH), 126.2 (CH), 126.8 (C), 127.7 (CH), 129.1 (CH), 129.6 (CH), (%) ϭ 353 (100) [MHϩ], 335 (31) [Mϩ Ϫ H2O], 237 (65). HRMS
129.8 (CH), 131.6 (C), 132.7 (CH), 139.7 (C), 145.8 (C), 154.4 (C,
q, JC,F ϭ 33.4 Hz), 156.4 (C) ppm. MS: m/z (%) ϭ 490 (10) [Mϩ
Ϫ TBS], 450 (32), 318 (59) [Mϩ Ϫ Ts, Ϫ OTBS], 133 (100). HRMS
(calcd. for C25H37F3NO2Si): 468.2546; found 468.2542.
(calcd. for C19H24F3N2O): 353.1841; found 353.1842.
17(Z)-{1-[3-[(Trifluoromethyl)-3H-1,2-diaziren-3-yl]phenyl]-
methylidene}de-A,B-androstan-8-one (3): PDC (279 mg, 0.74 mmol)
was added to a solution of 10 (130 mg, 0.37 mmol) in CH2Cl2
(13 mL). After stirring for 9 h the resulting suspension was filtered
through celite and concentrated. The resulting residue was purified
by flash chromatography (10% Et2O/hexanes) to afford 112 mg of
pure 3 [87% (2 steps), Rf ϭ 0.72 (40% Et2O/hexanes), colorless oil].
1H NMR (CDCl3, 250 MHz): δ ϭ 0.88 (s, 3 H, Me-18), 2.48 (m, 3
H), 6.23 (s, 1 H, H-20), 6.92 (m, 2 H, H-Ar), 7.18 (m, 2 H, H-Ar)
ppm. 13C NMR (CDCl3, 62.83 MHz): δ ϭ 19.3 (CH2), 19.3 (CH3),
23.4 (CH2), 28.3 (C, JC,F ϭ 40.2 Hz, C-CF3), 30.7 (CH2), 35.3
(CH2), 40.7 (CH2), 124.1 (CH), 50.6 (C), 61.3 (CH), 119.8 (CH),
122.1 (C, JC,F ϭ 274.7 Hz, CF3), 127.2 (CH), 128.2 (CH), 128.5
(C), 130.3 (CH), 139.0 (C), 152.7 (C), 210.9 (CϭO) ppm. MS
(FAB): m/z (%) ϭ 371 (8) [Mϩ ϩ Na], 349 (100) [MHϩ], 320 (15)
[Mϩ Ϫ N2H2]. HRMS (calcd. for C19H20F3N2O): 349.1528;
found 349.1527.
1H NMR (CDCl3, 250 MHz) [O-Ts (minor)]: δ ϭ 0.00 (s, 3 H,
MeSi), 0.01 (s, 3 H, MeSi), 0.89 (s, 9 H, tBuSi), 1.21 (s, 3 H, Me-
18), 2.43 (s, 3 H, Ar-Me), 2.63 (m, 1 H), 4.04 (m, 1 H), 6.13 (s, 1
H, H-20), 7.30 (d, J ϭ 8.2 Hz, 2 H, H-Ar), 7.35 (m, 4 H, H-Ar),
7.85 (d, J ϭ 8.3 Hz, 2 H, H-Ar) ppm. 13C NMR (CDCl3,
62.83 MHz) [O-Ts (minor)]: δ ϭ Ϫ5.2 (CH3), Ϫ4.9 (CH3), 17.5
(CH2), 18.0 (C), 20.7 (CH3), 21.7 (CH3), 23.0 (CH2), 25.8 (3 CH3),
31.0 (CH2), 34.2 (CH2), 37.2 (CH2), 44.6 (C), 52.5 (CH), 69.7
(CH),117.3 (CH),119.6 (CF3, q, JC,F ϭ 277.7 Hz), 123.8 (C), 125.6
(CH),127.9 (CH),129.1 (CH),129.2 (CH), 129.8 (CH),131.4 (C),
132.3 (CH),139.8 (C), 146.0 (C),154.3 (C, q, JC,F ϭ 33.4 Hz),
156.1 (C).
8β-tert-Butyldimethylsilyloxy-17(Z)-{1-[3-[(trifluoromethyl)-1,2-
diaziran-3-yl]phenyl]methylidene}de-A,B-androstane (precursor of
10): Liquid NH3 (2 mL) was added dropwise with a syringe to a
solution of tosylate 9 (400 mg, 0.643 mmol) in dry Et2O (30 mL)
atϪ78 °C. The resulting solution was stirred at Ϫ78 °C for 2 h
and then warmed to room temp. over 10 h before the reaction was
quenched with H2O (30 mL). The mixture was extracted with Et2O
and the combined organic fractions were dried, filtered, and con-
centrated in vacuo. The residue was purified by flash chromato-
graphy (3% EtOAc/hexanes) to give 300 mg of pure diaziridine
[99%, Rf ϭ 0.36 (8% EtOAc/hexanes), colorless oil]. 1H NMR
(CDCl3, 250 MHz): δ ϭ Ϫ0.01 (s, 3 H, MeSi), 0.00 (s, 3 H, MeSi),
0.87 (s, 9 H, tBuSi), 1.23 (s, 3 H, Me-18), 2.20 (broad s, 1 H, NH),
2.31 (m, 1 H), 2.62 (m, 1 H), 2.73 (broad s, 1 H, NH), 4.03 (s, 1
H),6.15 (s, 1 H, H-20), 7.23 (m, 2 H, H-Ar), 7.39 (m, 2 H, H-Ar)
ppm. 13C NMR (CDCl3, 62.83 MHz): δ ϭ Ϫ5.1 (CH3), Ϫ4.8
(CH3), 17.5 (CH2), 18.0 (C), 20.5 (CH3), 20.7 (CH3), 23.0 (CH2),
25.8 (3 CH3), 31.1 (CH2), 34.2 (CH2), 37.2 (CH2), 37.3 (CH2), 44.5
(C), 52.6 (CH), 58.0 (C, q, C-CF3, J ϭ 35.7 Hz), 69.7 (CH), 117.8
(CH), 123.6 (C, q, CF3, J ϭ 278.6 Hz), 125.4 (CH), 127.7 (CH),
129.1 (CH), 130.7 (C), 131.0 (C), 131.1 (CH), 139.6 (C), 155.5 (C),
155.6 (C) ppm. MS (FAB): m/z (%) ϭ 467 (100) [MHϩ], 452 (47)
[Mϩ Ϫ N], 409 (17) [Mϩ Ϫ C(CH3)3], 335 (60) [Mϩ Ϫ OTBS],
318 (15), 239 (21). HRMS (calcd. for C25H38F3N2OSi): 467.2706;
found 467.2701.
(17Z)-1α-tert-Butyldimethylsilyloxy-20-[3-[(trifluoromethyl)-3H-
1,2-diaziren-3-yl]phenyl]-17,20-didehydro-21,22,23,24,25,26,27-
heptanorvitamin D3 tert-Butyldimethylsilyl Ether (precursor of 2): A
solution of nBuLi (2.25 , 0.22 mL, 0.50 mmol) was added drop-
wise by syringe to a solution of the phosphane oxide 4 (325 mg,
0.558 mmol) in THF (9 mL) at Ϫ78 °C. The resulting deep red
solution was stirred at Ϫ78 °C for 1.5 h and a solution of ketone
3 (93 mg, 0.267 mmol) in THF (5 mL) was then added slowly. The
red solution was stirred in the dark at Ϫ78 °C for 4.5 h and then
warmed to Ϫ40 °C over 2 h. The reaction was quenched with H2O.
The mixture was extracted with Et2O and the combined organic
fractions were washed with brine, dried, filtered, and concentrated
in vacuo. The residue was purified by flash chromatography
(2Ϫ80% Et2O/hexanes) to give 184 mg of pure protected analog
[97%, Rf ϭ 0.81 (1% Et2O/hexanes), colorless oil]. 1H NMR
(CD2Cl2, 250 MHz): δ ϭ 0.09 (s, 6 H, Me2Si), 0.12 (s, 6 H, Me2Si),
0.91 (s, 9 H, tBuSi), 0.92 (s, 3 H, Me-18), 0.93 (s, 9 H, tBuSi), 4.22
(m, 1 H), 4.43 (m, 1 H), 4.91 (broad s, 1 H), 5.25 (broad s, 1 H),
6.27, 6.14 (AB, J ϭ 11.3 Hz, 2 H), 6.31 (s, 1 H, H-20), 6.99 (d, J ϭ
7.00 Hz, 1 H, H-Ar), 7.08 (s, 1 H, H-Ar), 7.28 (m, 2 H, H-Ar) ppm.
13C NMR (CD2Cl2, 62.83 MHz): δ ϭ Ϫ4.7 (CH3), Ϫ4.5 (CH3),
Ϫ4.4 (CH3), Ϫ4.3 (CH3), 18.6 (C), 18.7 (C), 19.0 (CH3), 22.9
(CH2), 23.7 (CH2), 26.2 (6 CH3), 29.0 (C, q, JC,F ϭ 40.3 Hz, C-
CF3), 29.2 (CH2), 32.1 (CH2), 37.4 (CH2), 45.5 (CH2), 46.6 (CH2),
47.8 (C), 56.9 (CH), 68.1 (CH), 72.6 (CH), 111.7 (CH2), 119.4
(CH),119.8 (CH), 122.9 (C, q, JC,F ϭ 274.7 Hz, CF3), 123.5 (CH),
124.3 (CH), 127.9 (CH), 128.6 (C), 128.8 (CH), 131.1 (CH), 136.4
(C), 140.4 (C), 140.4 (C), 149.1 (C), 155.8 (C).
17(Z)-{1-[3-[(Trifluoromethyl)-1,2-diaziran-3-yl]phenyl]-
methylidene}de-A,B-androstan-8β-ol (10): An aqueous solution of
HF (48%, 50 drops) was added dropwise to a solution of the previ-
ous diaziridine (200 mg, 0.429 mmol) in acetonitrile (10 mL). The
resulting heterogeneous mixture was stirred at room temp. for 2 h,
and then treated with saturated aqueous NaHCO3 and the aqueous
portion was extracted with Et2O. The combined organic fractions
were dried, filtered, and concentrated in vacuo. Flash chromato-
graphy (10Ϫ40% Et2O/hexanes) afforded 150 mg of 10 [99%, Rf ϭ
0.28 (40% Et2O/hexanes), colorless oil]. 1H NMR (CDCl3,
(17Z)-1α-20-[3-[(Trifluoromethyl)-3H-1,2-diaziren-3-yl]phenyl]-
17,20-didehydro-21,22,23,24,25,26,27-heptanorvitamin D3 (2): A so-
lution of TBAF (1.11  in THF, 3.7 mL, 4.13 mmol) was added by
syringe to a solution of the protected analog (140 mg, 0.196 mmol)
in THF (2 mL). After stirring at room temp. for 6 h in the dark, a
2532
Eur. J. Org. Chem. 2002, 2529Ϫ2534

Introduction of an Aryldiazirine Group into the Vitamin D Skeleton
FULL PAPER
Kerner, M. H. Hong, J. W. Pike, Mol. Endocrinol. 1996, 10,
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tracted with Et2O. The combined organic extracts were dried, fil-
tered, and concentrated in vacuo to give a residue that was purified
by flash chromatography (50Ϫ100% Et2O/hexanes) to afford 94 mg
of pure vitamin D analog 2 [99%, Rf ϭ 0.35 (50% EtOAc/hexanes),
pale yellow solid]. 1H NMR (CD2Cl2, 250 MHz): δ ϭ 0.80 (s, 3 H,
Me-18), 4.08 (m, 1 H), 4.30 (m, 1 H), 4.89 (1 H, broad s), 5.22
(broad s, 1 H), 6.20 (s, 1 H, H-20), 6.23, 6.01 (AB, J ϭ 11.1 Hz, 2
H), 6.88 (d, J ϭ 7.7 Hz, 1 H, H-Ar), 6.96 (s, 1 H, H-Ar), 7.20 (m,
2 H, H-Ar) ppm. 13C NMR (CD2Cl2, 62.83 MHz): δ ϭ 18.7 (CH3),
22.8 (CH2), 23.6 (CH2), 28.8 (C, q, JC,F ϭ 40.3 Hz, C-CF3), 29.2
(CH2), 31.8 (CH2), 37.1 (CH2), 43.3 (CH2), 45.6 (CH2), 47.7 (C),
56.7 (CH), 67.1 (CH), 71.0 (CH), 111.9 (CH2), 118.5 (CH), 119.7
(CH), 122.7 (C, q, JC,F ϭ 274.7 Hz, CF3), 124.2 (CH), 124.6 (CH),
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We thank the Spanish Ministry of Education and Culture for finan-
cial support (Grant PM97-0166), and for a doctoral F. P. U. fellow-
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and J. Zorgdrager (Solvay Pharmaceuticals BV, Weesp, The
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VDR is a ligand-dependent transcriptional regulator that be-
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C. H. Jin, S. A.
2533

´
A. Fernandez-Gacio, A. Mourin˜o
FULL PAPER
[13k]
[17]
[18]
Chem. Soc. 1995, 117, 3084Ϫ3095.
R. A. Tschirret-Guth,
Ketone 5 was prepared from commercially available vitamin
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´
´
´
K. F. Medzihradszky, P. R. Ortiz de Montellano, J. Am. Chem.
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A new method based on the use of radioiodinated 3-phenyltri-
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[14]
´
´
´
[19]
[20]
For similar examples, see: J. M. Delfino, S. L. Schreiber, F. M.
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MnO2/Et2O: E. Schmitz, R. Ohme, Org. Synth. 1965, 45,
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`
B. Figadere, A. W. Norman, H. L. Henry, H. P. Ko-
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[21]
[22]
[23]
[15c]
G. Grue-
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˜
´
´
´
1994 and refs. therein.
[16]
´
A. Fernandez-Gacio, C. Vitale, A. Mourin˜o, J. Org. Chem.
Received March 26, 2002
[O02168]
2000, 65, 6978Ϫ6983.
2534
Eur. J. Org. Chem. 2002, 2529Ϫ2534