Efficient synthesis of novel 1α-amino and 3β-amino analogues of 1α,25-dihydroxyvitamin D3

Article abstract of DOI:10.1021/jo026474t

Convenient synthetic routes to 1α-amino-25-hydroxyvitamin D₃ (3) and 3β-amino-3-deoxy-1α,25-dihydroxyvitamin D₃ (4), novel analogues of vitamin D₃ bearing an amino group at the C-1 or C-3 position, have been developed starting from (S)-(+)-carvone. Construction of the A-ring fragments was accomplished by selective enzymatic hydrolysis of a diester intermediate and introduction of the amino group under Mitsunobu conditions.

Full text of DOI:10.1021/jo026474t

Efficien t Syn th esis of Novel 1r-Am in o a n d
3â-Am in o An a logu es of
1r,25-Dih yd r oxyvita m in D3
Daniel Oves, Miguel Ferrero, Susana Ferna´ndez, and
Vicente Gotor*
Departamento de Quı´mica Orga´nica e Inorga´nica, Facultad
de Quı´mica, Universidad de Oviedo, 33071-Oviedo, Spain
vgs@sauron.quimica.uniovi.es
Received September 25, 2002
Abstr a ct: Convenient synthetic routes to 1R-amino-25-
hydroxyvitamin D3 (3) and 3â-amino-3-deoxy-1R,25-dihy-
droxyvitamin D3 (4), novel analogues of vitamin D3 bearing
an amino group at the C-1 or C-3 position, have been
developed starting from (S)-(+)-carvone. Construction of the
A-ring fragments was accomplished by selective enzymatic
hydrolysis of a diester intermediate and introduction of the
amino group under Mitsunobu conditions.
F IGURE 1. Vitamin D3, 1R,25-(OH)2-D3, 1R-amino-25-OH-
D3, 3â-amino-3-deoxy-1R,25-(OH)2-D3, and amino A-ring pre-
cursors.
while still maintaining significant biological activity.
Inversion of the natural orientation of the 1R-hydroxyl
by 1â results in an inhibitor of the nongenomic transcal-
tachia response.6 Replacement of a hydroxyl group to
fluorine results in paradoxical biological consequences.
Thus, 1R-fluoro-25-hydroxyvitamin D37 and 1R-F-25-OH-
Vitamin D3 (1, Figure 1) and its metabolites, among
them 1R,25-dihydroxyvitamin D3 [calcitriol, 2, 1R,25-
(OH)2-D3], the hormonally active form, exert control over
important physiological processes in the body related to
calcium and phosphorus metabolism, cell proliferation
and differentiation, and immune reactions.1 Various
derivatives of 1R,25-(OH)2-D3 have been proposed for the
treatment of rickets, osteoporosis, renal osteodystrophy,
certain cancers, psoriasis, AIDS, and Alzheimer’s
disease.1d,2 Most of the analogues have been developed
with the aim of improving the biological profile of the
natural hormone for potential therapeutic applications.
The biological functions of 1R,25-(OH)2-D3 are mediated
through its nuclear receptor (genomic actions), the nVDR,3
and by a membrane receptor that modulates rapid
nongenomic actions (transcaltachia).4 Therefore, inves-
tigation of the state of the binding domain is important
to elucidate the mechanism of the biological action.
The crucial role of the hydroxy groups at C-1 and C-25
for binding to the nVDR and DBP (vitamin D binding
protein) proteins has been established.5 However, struc-
tural changes at the 1-position of calcitriol can be made
8
16-ene-23-yne-D3 abolish all calcemic activity but elicit
cell differentiation. In contrast, Paaren et al.9 report that
1R,25-F2-D3 is biologically inert. Furthermore, Posner10
has shown that 1-hydroxyalkyl-25-hydroxyvitamin D3
analogues retain calcitriol’s antiproliferative activity in
murine keratinocytes even though these synthetic ho-
mologues are significantly less effective than calcitriol
in binding to the 1R,25-(OH)2-D3 receptor.
As part of our research program on the development
of A-ring modified vitamin D3 analogues,11 we describe
here the preparation of 1R-amino-25-hydroxyvitamin D3
(3) and 3â-amino-3-deoxy-1R,25-dihydroxyvitamin D3 (4),
novel analogues of vitamin D3 bearing an amino group
at the C-1 or C-3 position. It is of interest to know how
(5) (a) de Costa, B. R.; Holick, S. A.; Holick, M. F. J . Chem. Soc.,
Chem. Commun. 1989, 325-326. (b) Ikekawa, N. Med. Res. Rev. 1987,
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J . E.; Zhou, L.-X.; Nemere, I.; Zhao, J .; Muralidharan, R. K.; Okamura,
W. H. J . Biol. Chem. 1993, 268, 20022-20030. (b) Norman, A. W.;
Nemere, I.; Muralidharan, R. K.; Okamura, W. H. Biochem. Biophys.
Res. Commun. 1992, 189, 1450-1456.
(1) (a) Feldman, D., Glorieux, F. H., Pike, J . W., Eds. Vitamin D;
Academic Press: New York, 1997. (b) Ettinger, R. A.; DeLuca, H. F.
Adv. Drug Res. 1996, 28, 269-312. (c) Christakos, S.; Raval-Pandya,
M.; Wernyj, R. P.; Yang, W. Biochem. J . 1996, 316, 361-371. (d)
Bouillon, R.; Okamura, W. H.; Norman, A. W. Endocrinol. Rev. 1995,
16, 200-257.
(2) (a) Thacher, S. M.; Vasudevan, J .; Tsang, K.-Y.; Nagpal, S.;
Chandraratna, R. A. S. J . Med. Chem. 2001, 44, 281-297. (b) 1st
International Conference on Chemistry and Biology of Vitamin D
Analogues. Steroids-Special Issue 2001, 66, 127-472. (c) Vitamin D
Endocrine System: Structural, Biological, Genetic and Clinical Aspects;
Norman, A. W., Bouillon, R., Thomasset, M., Eds.; University of
California Riverside: Riverside, CA, 2000. (d) Tsugawa, N.; Nakagawa,
K.; Furobe, M.; Ono, Y.; Kubodera, N.; Ozono, K.; Okano, T. Biol.
Pharm. Bull. 2000, 23, 66-71.
(3) (a) DeLuca, H. F.; Krisinger, J .; Darwish, H. Kidney Int. (Suppl.)
1990, 29S, 2-8. (b) Minghetti, P. P.; Norman, A. W. FASEB J . 1988,
2, 3043-3053.
(4) (a) Norman, A. W.; Nemere, I.; Zhou, L. X.; Bishop, J . E.; Lowe,
K. E.; Maiyar, A. C.; Collins, E. D.; Taoka, T.; Sergeev, I.; Farach-
Carson, M. C. J . Steroid. Biochem. Mol. Biol. 1992, 41, 231-240. (b)
Deboland, A. R.; Nemere, I.; Norman, A. W. Biochem. Biophys. Res.
Commun. 1990, 166, 217-222.
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Y.; Tanaka, Y.; DeLuca, H. F. Chem. Pharm. Bull. 1984, 32, 3525-
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(8) Norman, A. W.; Zhou, J .; Henry, H. L.; Uskokovic, M. R.; Koeffler,
H. P. Cancer Res. 1990, 50, 6857-6864.
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Arch. Biochem. Biophys. 1981, 209, 579-583.
(10) (a) Posner, G. H.; Dai, H. BioMed. Chem. Lett. 1993, 3, 1829-
1834. (b) Posner, G. H.; Guyton, K. Z.; Kensler, T. W.; Barsony, J .;
Lieberman, M. E.; Reddy, G. S.; Clark, J . W.; Wankadiya, K. P.; Tserng,
K.-Y. BioMed. Chem. Lett. 1993, 3, 1835-1840. (c) Posner, G. H.; Dai,
H.; Afarinkia, K.; Murthy, N. N.; Guyton, K. Z.; Kensler, T. W. J . Org.
Chem. 1993, 58, 7209-7215. (d) Posner, G. H.; Nelson, T. D.; Guyton,
K. Z.; Kensler, T. W. J . Med. Chem. 1992, 35, 3280-3287.
(11) For recent papers: (a) Gotor-Ferna´ndez, V.; Ferrero, M.;
Ferna´ndez, S.; Gotor, V. J . Org. Chem. 2002, 67, 1266-1270. (b) D´ıaz,
M.; Ferrero, M.; Ferna´ndez, S.; Gotor, V. Tetrahedron: Asymmetry
2002, 13, 539-546. (c) D´ıaz, M.; Gotor-Ferna´ndez, V.; Ferrero, M.;
Ferna´ndez, S.; Gotor, V. J . Org. Chem. 2001, 66, 4227-4232. (d) D´ıaz,
M.; Ferrero, M.; Ferna´ndez, S.; Gotor, V. J . Org. Chem. 2000, 65, 5647-
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10.1021/jo026474t CCC: $25.00 © 2003 American Chemical Society
Published on Web 12/20/2002
1154
J . Org. Chem. 2003, 68, 1154-1157

SCHEME 1 a
SCHEME 3 a
a
i
Key: (a) Me2NNH2, 1,2-epoxypropane, PrOH, benzene, 50 f
70 °C, 7 h (41%).
SCHEME 2 a
a
Key: (a) TBDMSCl, imidazole, CH2Cl2, rt, 2 h (91%); (b)
MeONa, MeOH, rt, 2 h (quantitative); (c) p-nitrobenzoic acid, PPh3,
DEAD, THF, rt, 22 h (84%); (d) MeONa, MeOH, rt, 2 h (quantita-
tive); (e) phthalimide, PPh3, DEAD, THF, rt, 14 h, (68%); (f) (i)
MeNH2, EtOH, rt, 24 h, then 65 °C, 12 h, (ii) (Boc)2O, NaHCO3
(aq), CHCl3, rt, 24 h (83%).
ring/side chain fragment, has become one of the most
convenient methods for the synthesis of 1R,25-(OH)2-D3
analogues. For this, key A-ring precursors 5 and 6 (Figure
1) are required.
The strategy for the preparation of 5 began with the
stereoselective aziridination of (S)-(+)-carvone (Scheme
1), in a process similar to the stereoselective epoxidation14
of (S)-(+)-carvone used by Okamura for the synthesis of
the natural A-ring synthon.15 Subsequent modifications,
which include the SmI2-Pd0-mediated aziridine ring
opening, would provide enyne 5. Although the formation
of aziridines from the addition of nitrenes to olefins is a
general method,16 its utility here is limited by the
presence of an extra double bond and the nonstere-
ochemical control of the reaction. For this reason, aziri-
dination via Michael addition proves more useful. Among
all the methods tested, best results were obtained by
direct imination of (S)-(+)-carvone with aminimides.17
After several changes in the reaction conditions, the
aziridine 8 was obtained in 41% yield.
a
Key: (a) ref 15; (b) p-nitrobenzoic acid, PPh3, DEAD, THF,
rt, 2 h (87%); (c) Mg, MeOH, -30 °C, 6 h (56%); (d) ClCH2CO2H,
PPh3, DEAD, THF, rt, 1.5 h (86%); (e) CVL, 0.1 M KH2PO4 (pH
7)/1,4-dioxane (10:2), 30 °C, 5 h (92%); (f) phthalimide, PPh3,
DEAD, THF, rt, 5.5 h, (83%); (g) (i) MeNH2, EtOH, rt, 24 h, then
65 °C, 12 h, (ii) (Boc)2O, NaHCO3 (aq), CHCl3, rt, 24 h (51%); (h)
TBDMSCl, imidazole, CH2Cl2, rt, 2 h (92%).
the substitution of the 1R- or 3â-hydroxyl group by an
amino group can affect the affinities for the VDR and
DBP proteins, and consequently their biological proper-
ties. The amino function may change the hydrogen
bonding properties in the interaction between the recep-
tor and the analogue. Moreover, the different hydrophilic/
hydrophobic properties of these new derivatives may
provide interesting biological responses in the same way
that amino steroids have shown noteworthy pharmaco-
logical activity.12
An alternative approach to the above-mentioned pro-
cedure is a double inversion of the allylic hydroxyl group
under Mitsunobu18 conditions (Scheme 2). We used
alcohol 9 as starting material, an intermediate en route
to the 1R,25-(OH)2-D3 A-ring precursor from (S)-(+)-
carvone described by Okamura et al.15
Inversion of configuration at C-3 in 9 using p-nitroben-
zoic acid (PNBA) afforded p-nitrobenzoate ester 10 with
total inversion of the configuration and high yield. For
the selective deprotection of p-nitrobenzoate ester in the
presence of acetate ester, we decided to use magnesium
methoxide. The usefulness of this mild reagent for
selective cleavage of different esters is described in the
The amino derivatives 3 and 4 were synthesized
according to the enyne approach, originally developed by
Lythgoe.13 This method, based on the coupling between
an A-ring synthon enyne and an enol triflate of the CD-
(12) (a) Gasior, M.; Carter, R. B.; Witkin, J . M. Trends Pharmacol.
Sci. 1999, 20, 107-112. (b) Anderson, A.; Boyd, A. C.; Byford, A.;
Campbell, A. C.; Gemmell, D. K.; Hamilton, N. M.; Hill, D. R.; Hill-
Venning, C.; Lambert, J . J .; Maidment, M. S.; May, V.; Marshall, R.
J .; Peters, J . A.; Rees, D. C.; Stevenson, D.; Sundaram, H. J . Med.
Chem. 1997, 40, 1668-1681. (c) Marshall, F. H.; Stratton, S. C.;
Mullings, J .; Ford, E.; Worton, S. P.; Oakley, N. R.; Hagan, R. M.
Pharmacol. Biochem. Behav. 1997, 58, 1-8.
(14) Klein, E.; Ohloff, G. Tetrahedron 1963, 19, 1091-1099.
(15) Okamura, W. H.; Aurrecoechea, J . M.; Gibbs, R. A.; Norman,
A. W. J . Org. Chem. 1989, 54, 4072-4083.
(16) For general reviews: (a) Atkinson, R. S. Tetrahedron 1999, 55,
1519-1559. (b) Sweeney, J .; Osborn, H. M. I. Tetrahedron: Asymmetry
1997, 11, 1693-1715.
(13) Harrison, R. G.; Lythgoe, B.; Wright, P. W. J . Chem. Soc., Perkin
Trans. 1 1974, 2654-2657.
(17) Ikeda, I.; Machii, Y.; Okahara, M. Synthesis 1980, 650-651.
(18) Mitsunobu, O. Synthesis 1981, 1-28.
J . Org. Chem, Vol. 68, No. 3, 2003 1155

SCHEME 4 a
a
Key: (a) Pd(PPh3)2(OAc)2, CuI, Et2NH, DMF, rt, 1 h; (b) Bu4NF, THF, rt, 12 h (78% for 23 and 91% for 24, two steps); (c) H2, Lindlar
catalyst, quinoline, MeOH, rt, 20 min; (d) acetone, 80 °C, 4 h (64% for 27 and 72% for 28, two steps); (e) HCl(g), EtOH, rt, 30 min (72%).
literature.19 When substrate 10 was subjected to Mg/
MeOH conditions, only moderate selectivity in removing
PNB with respect to acetate was observed. We investi-
gated several reaction conditions (best results were
obtained at -30 °C using 5 equiv of Mg) but the highest
yield achieved was 56% after flash chromatography. In
addition to the monoalcohol 11, starting material 10 and
the corresponding diol from the deprotection of both
esters, were isolated.
An efficient alternative for the selective manipulation
of functional groups of similar reactivity is the use of
biocatalysts, especially lipases. Applications of enzymes
as catalysts in organic synthesis have been enhanced
greatly in the past decade.20 We previously described11a
how enzymatic hydrolysis of diester 10 takes place with
total selectivity, but noted that most of the enzymes we
tested led to cleavage of the acetate ester in preference
to the p-nitrobenzoate. The enzyme probably cannot
accommodate a group as large as p-nitrobenzoyl in the
active site. However, inversion of the allylic alcohol 9
under Mitsunobu conditions using chloroacetic acid, and
the subsequent hydrolysis of 12 catalyzed by Chromo-
bacterium viscosum lipase (CVL),21 gave exclusively
monoacetate 11. CVL selectively hydrolyzes the C-3
chloroacetate ester instead of the C-5 acetate. When
alcohol 11 was allowed to react with phthalimide in the
presence of DEAD and PPh3, phthalimide derivative 13
was obtained with complete inversion of the configura-
tion. The reaction of 13 with 8 M MeNH2 in EtOH results
in complete deprotection of both the hydroxy and the
amino groups to give the corresponding amino alcohol,
which is N-protected by adding di-tert-butyl dicarbonate
to the reaction mixture. The resulting product 14
is conveniently protected as a tert-butyldimethylsilyl
ether.
The synthesis of 3â-amino A-ring fragment 6 is out-
lined in Scheme 3. First, silylation of alcohol 9 led to 16,
which was saponified using MeONa in MeOH followed
by neutralization with ammonium chloride; when acid
was used to cleave the ester, concomitant desilylation
occurred. Inversion of alcohol 17 and subsequent saponi-
fication (as above) gave derivative 19. Finally, treatment
of the latter with phthalimide using the Mitsunobu
procedure, deprotection of the amino group with methy-
lamine, and protection as the N-Boc derivative afforded
A-ring precursor 21.
Coupling22 of A-ring synthons 15 and 21 with the CD-
triflate 22, prepared according to the published proce-
dure,23 using bis(triphenylphosphine)palladium(II) ac-
etate-copper(I) iodide catalyst and desilylation, then
produced dienynes 23 and 24, respectively (Scheme 4).
Catalytic hydrogenation of amino alcohols 23 and 24 in
deoxygenated MeOH, in the presence of Lindlar catalyst
and quinoline, generated previtamins 25 and 26. Ther-
molysis of the latter at 80 °C for 4 h followed by
deprotection of the amino group with HCl yielded 3 and
4, which were isolated as their hydrochloride salts.
In conclusion, we have synthesized two novel analogues
of 1R,25-(OH)2-D3, each bearing an amino group in the
A-ring fragment. Key features in the synthesis of corre-
sponding A-ring synthons 15 and 21 are the excellent
selectivity exhibited by Chromobacterium viscosum lipase
in the hydrolysis of diester 11 and the direct replacement
(19) Xu, Y.-C.; Bizuneh, A.; Walker, C. Tetrahedron Lett. 1996, 37,
455-458.
(20) (a) Ferna´ndez, S.; Gotor-Ferna´ndez, V.; Ferrero, M.; Gotor, V.
Curr. Org. Chem. 2002, 6, 453-469. (b) Koeller, K. M.; Wong, C.-H.
Nature 2001, 409, 232-240. (c) Klibanov, A. M. Nature 2001, 409, 241-
246. (d) Stereoselective Biocatalysis; Patel, R. N., Ed.; Marcel Dekker:
New York, 2000. (e) Ferrero, M.; Gotor, V. Chem. Rev. 2000, 4319-
4347. (f) Bornscheuer, U. T.; Kazlauskas, R, J . Hydrolases in Organic
Synthesis: Regio- and Stereoselective Biotransformations; Wiley-
VCH: Weinheim, 1999.
(22) (a) Mascaren˜as, J . L.; Sarandeses, L. A.; Castedo, L.; Mourin˜o,
A. Tetrahedron 1991, 47, 3485-3498. (b) Barrack, S. A.; Gibbs, R. A.;
Okamura, W. H. J . Org. Chem. 1988, 53, 1790-1796.
(23) (a) Maynard, D. F.; Trankle, W. G.; Norman, A. W.; Okamura,
W. H. J . Med. Chem. 1994, 37, 2387-2393. (b) Also see refs 11d and
22.
(21) CVL (freeze-dried, 4500 U/mg powder) from Genzyme.
1156 J . Org. Chem., Vol. 68, No. 3, 2003

of the hydroxyl group by a phthalimide group with strict
inversion of the configuration using Mitsunobu condi-
tions.
ship. We thank Robin Walker for the English language
revision of the manuscript.
Su p p or tin g In for m a tion Ava ila ble: Experimental pro-
cedures and complete 1H and 13C NMR spectral data in
addition to mp, IR, microanalysis, and MS data for the new
compounds. The level of purity is indicated by the inclusion
of copies of 1H and 13C NMR spectra. This material is available
free of charge via the Internet at http://pubs.acs.org.
Ack n ow led gm en t. We thank Genzyme for the
generous gift of the lipase CVL. This work has been
supported by grants from MCYT (Spain; Project PPQ-
2001-2683) and the Principado de Asturias (Spain;
Project GE-EXP01-03). S. F. thanks MCYT for a per-
sonal grant (Ramo´n y Cajal Program). D. O. thanks III
PRI (Principado de Asturias) for a predoctoral fellow-
J O026474T
J . Org. Chem, Vol. 68, No. 3, 2003 1157