Synthesis of 4-azasteroids by an intramolecular Ugi reaction

Article abstract of DOI:10.1016/j.steroids.2008.06.002

In this paper we report the use of an intramolecular Ugi reaction to synthesize new 4-azacholestanes diversely substituted both at N-4 and C-5. Both the scope and the stereochemical outcome of this approach were studied by varying the nature of the compon

Full text of DOI:10.1016/j.steroids.2008.06.002

steroids 7 3 ( 2 0 0 8 ) 1270–1276
available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/steroids
Synthesis of 4-azasteroids by an intramolecular Ugi reaction
Fernando Alonso, Sofía L. Acebedo, Andrea C. Bruttomesso, Javier A. Ramírez∗
Departamento de Química Orgánica and UMYMFOR (CONICET-Facultad de Ciencias Exactas y Naturales),
Universidad de Buenos Aires, Pabellón 2, Piso 3, Ciudad Universitaria, C1428EGA Buenos Aires,
Argentina
a r t i c l e i n f o
a b s t r a c t
Article history:
In this paper we report the use of an intramolecular Ugi reaction to synthesize new 4-
azacholestanes diversely substituted both at N-4 and C-5.
Received 18 April 2008
Accepted 12 June 2008
Published on line 21 June 2008
Both the scope and the stereochemical outcome of this approach were studied by varying
the nature of the components necessary for this multicomponent reaction.
In sight of our results we concluded that this methodology can be applied to obtain 4-
azasteroids targeted to find new biologically active compounds.
Keywords:
© 2008 Elsevier Inc. All rights reserved.
Azasterols
4-Azacholestanes
Multicomponent reaction
Ugi reaction
1.
Introduction
achieve them. This strategy should be based on a simple and
fast generation of new compounds having a high structural
The replacement of one or more carbon atoms of a steroid
molecule by a heteroatom affects its chemical properties and
often results in useful alterations to its biological activity.
Azasteroids specially feature numerous biological activities
[1]. Among the large and heterogeneous group of azas-
teroids, 4-azasteroids have attracted much interest, as many
4-azalactams exhibit strong inhibition of human steroid 5␣-
reductase, making them potential drugs for the treatment
of benign prostatic hyperplasia [2]. Finasteride (1) and tur-
osteride (2) are two commercial drugs belonging to this class
(Fig. 1).
diversity. Multicomponent reactions are best suited to achieve
this goal.
Multicomponent reactions (MCRs) are generally defined as
reactions where more than two starting materials react to
form a product, incorporating essentially all of the atoms of
the educts. The structure of the reaction product can be easily
diversified by a systematic variation of the starting materials
[4].
One of the most versatile MCRs is the Ugi four-component
reaction (U-4CR), which is based on the exceptional reactivity
of the isocyanide functional group [5].
In addition, some 4-azasteroids, such as the cholestane
derivative 3 (Fig. 1), have been shown to have interest-
ing antifungal and antibacterial properties that are strongly
dependent on the structural features of the studied com-
pounds [3].
Taking the broad spectrum of biological properties of 4-
azasteroids into account, our group started a research program
devoted to the development of new synthetic strategies to
U-4CR constitutes a homogeneous group of reactions in
which an amino component, an acid, a carbonyl compound
and an isocyanide react together to give an ␣-aminoacylamide
[4,5].
Intramolecular versions of the U-4CR, where two of the
four functional groups involved belong to the same molecule,
are particularly interesting for their ability to generate vari-
ous heterocycles [6,7]. In this paper we report a new synthetic
∗
Corresponding author. Tel.: +54 1145763346; fax: +54 1145763385.
E-mail address: jar@qo.fcen.uba.ar (J.A. Ramírez).
0039-128X/$ – see front matter © 2008 Elsevier Inc. All rights reserved.
doi:10.1016/j.steroids.2008.06.002

steroids 7 3 ( 2 0 0 8 ) 1270–1276
1271
(C19); 18.6 (C21); 22.0; 22.5 and 22.8 (C26 and C27); 23.8; 23.9;
26.7; 27.9; 28.2; 29.1; 29.3 (C2); 29.6; 33.6; 35.7; 36.1; 39.4;
39.7; 41.1 (NHCH2COOCH3); 41.4 (C10); 42.6 (C13); 43.9; 45.6
(CH2Ph); 45.7; 52.2 (NHCH2COOCH3); 55.5; 56.0; 70.9 (C5); 127.3;
128.4; 128.7; 139.1; 169.9 (CONHCH2COOCH3); 173.7 (C3); 173.8
(CONHCH2COOCH3). Anal. Calcd. for C38H58N2O4: C, 75.21; H,
9.63; N, 4.62. Found: C, 75.33; H, 9.62; N, 4.59.
2.1.4. 4-Benzyl-5-N-(methoxycarbonylmethylen)-
carboxamido-4-aza-5ˇ-cholestan-3-one (5b)
M.p.: 155–156 ◦C. MS m/z (%): 606 (M+, 0.2), 577 (0.5), 476 (95.2),
200 (22.9), 91 (100). 1H NMR: 0.40 (7␣-H, 1H, m); 0.62 (18-H, 3H,
s); 0.86 and 0.87 (26-H and 27-H, 3H, d, J = 2.3 Hz); 0.89 (H-21,
3H, d, J = 6.4 Hz); 0.99 (19-H, 3H, s); 2.53 and 2.59 (2-H, 2H, m);
3.58 and 3.81 (NHCH2COOCH3, 2H, dd, J = 6.0 and 18.5 Hz); 3.67
(NHCH2COOCH3, 3H, s); 4.41 and 4.81 (CH2Ph, 2H, d, J = 15.4 Hz);
6.33 (NHCH2COOCH3, 1H, t, J = 5.6 Hz); 7.26 (CH2Ph, 5H, m).
13C NMR: 11.9 (C18); 18.6 (C21); 19.4 (C19); 21.0; 22.5 and 22.8
(C26 and C27); 23.8; 26.2; 26.8; 27.4; 28.0; 28.2; 28.5 (C2); 34.0;
35.7; 36.1; 38.1 (C10); 39.5; 39.8; 41.5 (NHCH2COOCH3); 42.2;
42.3 (C13); 47.5 (CH2Ph); 52.2 (NHCH2COOCH3); 56.1; 56.2; 73.8
(C5); 127.1; 128.2; 128.8; 138.5; 170.0 (CONHCH2COOCH3); 172.4
Fig. 1 – Examples of bioactive 4-azasteroids.
procedure to obtain 4-azasteroids, substituted at C-5, based
on the intramolecular U-4CR between a bifunctional steroidal
oxoacid and several amines and isocyanides.
(CONHCH2COOCH3); 173.5 (C3). Anal. Calcd. for C38H58N2O4: C,
75.21; H, 9.63; N, 4.62. Found: C, 75.19; H, 9.70; N, 4.65.
2.
Experimental
2.1.
Synthesis
2.1.5. 4-Benzyl-5-N-(diethoxyphosphorylmethylen)-
carboxamido-4-aza-5˛-cholestan-3-one (6a)
Colorless oil. MS m/z (%): 476 (M+–CONHPO(OEt)2, 0.3), 332 (1.2),
91 (8.4), 43 (100). 1H NMR: 0.63 (18-H, 3H, s); 0.85 and 0.86 (26-H
and 27-H, 3H, d, J = 2.5 Hz); 0.88 (H-21, 3H, d, J = 6.7 Hz); 0.92 (19-
H, 3H, s); 1.33 and 1.37 (NHCH2PO(OCH2CH3)2, 6H, t, J = 7.1 Hz);
2.60 (2-H, 2H, m); 3.28 and 3.71 (NHCH2PO(OCH2CH3)2, 2H,
ddd, J = 6.9, 11.6 and 15.8 Hz); 4.12 (NHCH2PO(OCH2CH3)2, 4H,
m); 4.65 and 4.84 (CH2Ph, 2H, d, J = 15.1 Hz); 6.07 (NHCH2
PO(OCH2CH3)2, 1H, t, J = 5.7 Hz); 7.30 (CH2Ph, 5H, m). 13C
NMR: 12.0 (C18); 16.0 (C19); 16.4 (CONHCH2PO(OCH2CH3)2,
J = 6.0 Hz); 18.6 (C21); 22.1; 22.5 and 22.8 (C26 and C27);
23.8; 23.9; 26.7; 27.9; 28.2; 29.1; 29.2 (C2); 29.5; 33.6; 34.4
(CONHCH2PO(OCH2CH3)2, J = 154.6 Hz); 35.7; 36.1; 39.4; 39.7;
41.8 (C10); 42.6 (C13); 45.6 (CH2Ph); 45.7; 55.6; 56.0; 62.3 and
62.5 (CONHCH2PO(OCH2CH3)2, J = 5.8 Hz); 71.0 (C5); 127.4; 128.3;
128.8; 139.0; 172.7 (CONHCH2PO(OCH2CH3)2, J = 3.1 Hz); 173.7
(C3). Anal. Calcd. for C39H63N2O5P: C, 69.82; H, 9.46; N, 4.18.
Found: C, 69.95; H, 9.45; N, 4.20.
2.1.1. General
All the reagents were purchased from Sigma–Aldrich Chem-
ical Co. EI-MS were measured either in a VG Trio-2 or in a
Shimadzu QP-5000 mass spectrometer at 70 eV by direct inlet.
Melting points were determined on a Fisher Johns apparatus
and are uncorrected. All NMR spectra were recorded in CDCl3
on a Bruker AM-500 (500 MHz for 1H and 125.1 MHz for 13C).
Chemical shifts (ı) are given in ppm downfield from TMS as
the internal standard. Coupling constant (J) values are in Hz.
All solvents and reagents were of analytical grade.
All new compounds gave satisfactory NMR and mass spec-
tral/combustion analysis data.
2.1.2. General synthetic procedure
The oxoacid 4 (5-oxo-A-nor-3,5-secocholestan-3-oic acid [8],
50 mg) was dissolved in methanol or ethanol and 1 equiva-
lent of the corresponding amine was added. The mixture was
stirred for 15 min at room temperature and 1 equivalent of
the isonitrile was added. The reaction was refluxed for 16 h.
The solvent was evaporated under reduced pressure and the
residue was taken in EtOAc and washed with NaOH (5% aq).
The mixture of epimers was separated by silica gel column
chromatography (hexane/EtOAc gradient).
2.1.6. 4-Benzyl-5-N-(diethoxyphosphorylmethylen)-
carboxamido-4-aza-5ˇ-cholestan-3-one (6b)
Colorless oil. MS m/z (%): 476 (M+–CONHPO(OEt)2, 0.4), 332
(1.5), 91 (9.3), 43 (100). 1H NMR: 0.45 (7␣-H, 1H, m); 0.72 (18-
H, 3H, s); 0.85 and 0.86 (26-H and 27-H, 3H, d, J = 2.4 Hz);
0.88 (H-21, 3H, d, J = 6.9 Hz); 0.99 (19-H, 3H, s); 1.31 and 1.35
(NHCH2 PO(OCH2CH3)2, 3H, t, J = 7.0 Hz); 2.54 (2-H, 2H, m);
3.21 and 3.63 (NHCH2PO(OCH2CH3)2, 2H, ddd, J = 6.0, 13.0 and
17.1 Hz); 4.09 (NHCH2PO(OCH2CH3)2, 4H, m); 4.39 and 4.77
(CH2Ph, 2H, d, J = 14.6 Hz); 6.11 (NHCH2PO(OCH2CH3)2, 1H, t,
J = 6.0 Hz); 7.28 (CH2Ph, 5H, m). 13C NMR: 11.9 (C18); 16.4
(CONHCH2PO(OCH2CH3)2, J = 6.0 Hz); 18.6 (C21); 19.4 (C19); 21.0;
22.5 and 22.8 (C26 and C27); 23.8; 26.2; 26.8; 27.4; 28.0; 28.5 (C2);
34.0; 34.6 (CONHCH2PO(OCH2CH3)2, J = 150.0 Hz); 35.7; 36.1; 38.2
(C10); 39.5; 39.8; 42.3; 42.6 (C13); 47.4 (CH2Ph); 56.0; 56.1; 62.3
2.1.3. 4-Benzyl-5-N-(methoxycarbonylmethylen)-
carboxamido-4-aza-5˛-cholestan-3-one (5a)
M.p.: 177–178 ◦C. MS m/z (%): 606 (M+, 0.1), 577 (0.5), 476 (97.2),
200 (20.9), 91 (100). 1H NMR: 0.62 (18-H, 3H, s); 0.85 and 0.86 (26-
H and 27-H, 3H, d, J = 2.3 Hz); 0.88 (H-21, 3H, d, J = 6.4 Hz); 0.92
(19-H, 3H, s); 2.62 (2-H, 2H, m); 3.68 and 3.87 (NHCH2COOCH3,
2H, dd, J = 5.7 and 17.7 Hz); 3.69 (NHCH2COOCH3, 3H, s); 4.66
and 4.91 (CH2Ph, 2H, d, J = 14.8 Hz); 6.27 (NHCH2COOCH3, 1H,
t, J = 5.7 Hz); 7.30 (CH2Ph, 5H, m). 13C NMR: 12.0 (C18); 16.0

1272
steroids 7 3 ( 2 0 0 8 ) 1270–1276
and 62.5 (CONHCH2PO(OCH2CH3)2, J = 5.8 Hz); 73.9 (C5); 127.1;
128.3; 128.9; 138.4; 171.7 (CONHCH2PO(OCH2CH3)2, J = 2.9 Hz);
173.5 (C3). Anal. Calcd. for C39H63N2O5P: C, 69.82; H, 9.46; N,
4.18. Found: C, 69.83; H, 9.39; N, 4.25.
(2-H, 2H, m); 3.13 and 3.29 (NCH2(CH2)2CH3, 2H, m, J = 4.5
and 11.3 Hz); 3.79 (NHCH(CH2)5, 1H, m); 5.50 (NHCH(CH2)5,
1H, d, J = 8.2 Hz). 13C NMR: 11.9 (C18); 13.7 (NCH2(CH2)2CH3);
18.6 (C21); 20.8; 19.7 (C19); 21.0; 22.5 and 22.8 (C26 and C27);
23.8; 24.0; 24.6; 24.8; 25.4; 27.1; 27.5; 28.0; 28.2; 28.4 (C2); 30.8;
32.7; 33.2; 34.4; 35.7; 36.1; 37.7 (C10); 39.5; 39.8; 42.2; 42.3
(C13); 45.0 (NCH2(CH2)2CH3); 48.8 (NHCH(CH2)5); 56.2; 56.1;
73.1 (C5); 171.0 (C3); 172.5 (CONHCH(CH2)5). Anal. Calcd. for
C37H64N2O2: C, 78.11; H, 11.34; N, 4.92. Found: C, 78.02; H, 11.21;
N, 4.97.
2.1.7. 4-Benzyl-5-N-cyclohexylcarboxamido-4-aza-
5˛-cholestan-3-one (7a)
M.p.: 160–160 ◦C. MS m/z (%): 602 (M+, 0.2), 587 (0.5), 476
(50.1), 387 (3.2), 200 (16.8), 91 (100). 1H NMR: 0.65 (18-H, 3H,
s); 0.84 and 0.88 (26-H and 27-H, 3H, d, J = 2.3 Hz); 0.90 (H-
21, 3H, d, J = 6.5 Hz); 0.91 (19-H, 3H, s); 2.47 (2-H, 2H, m);
3.49 (NHCH(CH2)5, 1H, m); 4.38 and 5.10 (NCH2Ph, 2H, d,
J = 14.8 Hz); 5.38 (NHCH(CH2)5, 1H, d, J = 7.9 Hz); 7.36 (Ph, 5H,
m). 13C NMR: 12.0 (C18); 16.6 (C19); 18.6 (C21); 22.4; 22.5 and
22.8 (C26 and C27); 23.8; 24.0; 24.8; 25.4; 26.8; 27.9; 28.2; 29.7
(C2); 29.9; 30.0; 31.5; 32.2; 32.5; 34.3; 35.8; 36.1; 39.4; 39.4; 39.9;
42.1 (C10); 42.7 (C13); 45.3 (NCH2Ph); 48.1 (NHCH(CH2)5); 46.6;
55.5; 56.0; 70.5 (C5); 127.7; 129.0; 129.1; 139.2; 172.3 (C3); 173.8
(CONHCH(CH2)5). Anal. Calcd. for C40H62N2O2: C, 79.68; H,
10.36; N, 4.65. Found: C, 79.83; H, 9.99; N, 4.55.
2.1.11. 4-(2ꢀ-Phenylethyl)-5-N-cyclohexylcarboxamido-
4-aza-5˛-cholestan-3-one (9a)
M.p.: 140–141 ◦C. MS m/z (%): 617 (M+, 0.7), 602 (0.5), 491 (100),
387 (5.9), 214 (8.5), 105 (15.5). 1H NMR: 0.68 (18-H, 3H, s);
0.86 and 0.87 (26-H and 27-H, 3H, d, J = 2.3 Hz); 0.90 (H-21,
3H, d, J = 6.5 Hz); 0.99 (19-H, 3H, s); 2.56 and 2.40 (2-H, 2H,
m); 2.70 and 3.07 (NCH2CH2Ph, 2H, m, J = 5.0 and 12.2 Hz);
3.32 and 3.88 (NCH2CH2Ph, 2H, m, J = 4.9, 18.2 and 12.0 Hz);
3.68 (NHCH(CH2)5, 1H, m); 5.60 (NHCH(CH2)5, 1H, d, J = 7.9 Hz);
7.28 (Ph, 5H, m). 13C NMR: 12.1 (C18); 15.5 (C19); 18.6 (C21);
22.1; 22.5 and 22.8 (C26 and C27); 23.9; 24.0; 24.6; 24.7; 25.4;
26.8; 28.0; 28.3; 28.9; 29.0; 29.2 (C2); 32.6; 32.8; 33.5; 35.8; 36.0
(NCH2CH2Ph); 36.1; 39.4; 39.8; 41.1 (C10); 44.2 (NCH2CH2Ph);
48.3 (NHCH(CH2)5); 42.6 (C13); 45.4; 55.7; 56.1; 69.7 (C5); 126.6;
128.6; 128.7; 138.8; 172.5 (C3); 172.7 (CONHCH(CH2)5). Anal.
Calcd. for C41H64N2O2: C, 79.82; H, 10.46; N, 4.54. Found: C,
79.77; H, 10.39; N, 4.32.
2.1.8. 4-Benzyl-5-N-cyclohexylcarboxamido-4-aza-
5ˇ-cholestan-3-one (7b)
M.p.: 102–103 ◦C. MS m/z (%): 602 (M+, 0.2), 587 (0.7), 476 (51.1),
387 (3.7), 200 (17.0), 91 (100). 1H NMR: 0.43 (7␣-H, 1H, m); 0.62
(18-H, 3H, s); 0.85 and 0.88 (26-H and 27-H, 3H, d, J = 2.3 Hz); 0.90
(H-21, 3H, d, J = 6.5 Hz); 0.99 (19-H, 3H, s); 2.55 (2-H, 2H, m); 3.57
(NHCH(CH2)5, 1H, m); 4.23 and 4.86 (NCH2Ph, 2H, d, J = 15.2 Hz);
5.41 (NHCH(CH2)5, 1H, d, J = 7.6 Hz); 7.25 (Ph, 5H, m). 13C NMR:
11.8 (C18); 18.6 (C21); 19.7 (C19); 21.0; 22.5 and 22.8 (C26 and
C27); 23.8; 24.6; 25.4; 26.3; 27.1; 27.4; 28.0; 28.2; 28.5 (C2); 32.5;
32.9; 34.1; 35.7; 36.1; 38.0 (C10); 39.5; 39.7; 42.1; 42.2 (C13); 47.7
(NCH2Ph); 48.8 (NHCH(CH2)5); 56.0; 56.2; 73.7 (C5); 127.0; 128.2;
128.9; 138.5; 170.6 (C3); 173.5 (CONHCH(CH2)5). Anal. Calcd. for
2.1.12. 4-(2ꢀ-Phenylethyl)-5-N-cyclohexylcarboxamido-
4-aza-5ˇ-cholestan-3-one (9b)
M.p.: 225–228 ◦C. MS m/z (%): 617 (M+, 0.6), 602 (0.6), 491 (100),
387 (6.2), 214 (8.2), 105 (14.0). 1H NMR: 0.67 (18-H, 3H, s); 0.85
and 0.87 (26-H and 27-H, 3H, d, J = 2.3 Hz); 0.90 (H-21, 3H,
d, J = 6.5 Hz); 1.02 (19-H, 3H, s); 2.03 and 2.51 (2-H, 2H, m);
2.79 and 2.92 (NCH2CH2Ph, 2H, m, J = 4.5 and 12.0 Hz); 3.35
and 3.42 (NCH2CH2Ph, 2H, m, J = 4.9, 12.1 and 20.0 Hz); 3.77
(NHCH(CH2)5, 1H, m); 5.50 (NHCH(CH2)5, 1H, d, J = 8.2 Hz); 7.25
(Ph, 5H, m). 13C NMR: 11.8 (C18); 18.6 (C21); 19.7 (C19); 21.0; 22.5
and 22.8 (C26 and C27); 23.8; 24.0; 24.8; 25.4; 27.1; 27.2 (C2); 27.5;
28.0; 28.2; 28.5; 32.8; 33.2; 34.4; 34.9 (NCH2CH2Ph); 35.7; 36.1;
37.8 (C10); 39.5; 39.8; 42.2; 42.3 (C13); 46.9 (NCH2CH2Ph); 48.9
(NHCH(CH2)5); 56.0; 56.1; 73.1 (C5); 126.3; 128.5; 128.7; 139.4;
170.9 (C3); 172.8 (CONHCH(CH2)5). Anal. Calcd. for C41H64N2O2:
C, 79.82; H, 10.46; N, 4.54. Found: C, 79.90; H, 10.35; N,
4.61.
C40H62N2O2: C, 79.68; H, 10.36; N, 4.65. Found: C, 79.54; H, 10.44;
N, 4.72.
2.1.9. 4-Butyl-5-N-cyclohexylcarboxamido-4-aza-
5˛-cholestan-3-one (8a)
M.p.: 219–220 ◦C. MS m/z (%): 568 (M+, 37.5), 553 (2.3), 444 (100),
166 (39.2), 83 (16.5). 1H NMR: 0.66 (18-H, 3H, s); 0.86 and 0.87
(26-H and 27-H, 3H, d, J = 2.3 Hz); 0.89 (H-21, 3H, d, J = 6.2 Hz);
0.88 (NCH2(CH2)2CH3, 3H, t, J = 7.2 Hz); 0.93 (19-H, 3H, s); 2.42
(2-H, 2H, m); 3.19 and 3.62 (NCH2(CH2)2CH3, 2H, m, J = 4.7
and 13.2 Hz); 3.67 (NHCH(CH2)5, 1H, m); 5.67 (NHCH(CH2)5,
1H, d, J = 7.7 Hz). 13C NMR: 12.1 (C18); 13.8 (NCH2(CH2)2CH3);
15.5 (C19); 18.6 (C21); 20.5; 22.1; 22.5 and 22.8 (C26 and C27);
23.9; 24.0; 24.6; 24.8; 25.4; 26.7; 28.0; 28.3; 29.0 (C2); 29.1; 29.2;
32.1; 32.6; 32.7; 33.6; 35.8; 36.1; 39.5; 39.8; 41.1 (C10); 42.0;
42.6 (C13); 45.5 (NCH2(CH2)2CH3); 48.2 (NHCH(CH2)5); 55.7; 56.1;
69.6 (C5); 172.6 (C3); 172.7 (CONHCH(CH2)5). Anal. Calcd. for
2.1.13. 4-(2ꢀ-(1H-benzo[b]azol-3-yl)ethyl)-5-N-
cyclohexylcarboxamido-4-aza-5˛-cholestan-3-one (10a)
Colorless oil. MS m/z (%): 656 (M+, 0.3), 529 (4.2), 476 (51.1),
386 (16.4), 143 (100), 83 (9.2). 1H NMR: 0.68 (18-H, 3H, s); 0.85
and 0.86 (26-H and 27-H, 3H, d, J = 2.3 Hz); 0.91 (H-21, 3H, d,
J = 6.5 Hz); 1.01 (19-H, 3H, s); 2.45 (2-H, 2H, m); 2.89 and 3.52
(NCH2CH2Ar, 2H, m, J = 5.0 and 12.1 Hz); 3.61 (NHCH(CH2)5, 1H,
m); 3.22 and 3.94 (NCH2CH2Ar, 2H, m, J = 4.0 and 13.0 Hz); 5.7
(NHCH(CH2)5, 1H, d J = 8.1 Hz); 7.2 (Ar, 3H, m); 7.37 (Ar, 1H, m);
7.77 (Ar, 1H, m); 8.27 (Ar, 1H, s). 13C NMR: 12.1 (C18); 15.7 (C19);
18.6 (C21); 22.2; 22.5 and 22.8 (C26 and C27); 23.9; 24.0; 24.7;
24.8; 25.3; 25.8; 26.8; 28.0; 28.3; 29.0; 29.1 (C2); 29.3; 32.5; 32.6;
33.6; 35.8; 36.1; 39.4; 39.8; 41.3 (C10); 42.6 (C13); 43.0; 45.6; 48.3
C37H64N2O2: C, 78.11; H, 11.34; N, 4.92. Found: C, 78.31; H, 10.89;
N, 4.82.
2.1.10. 4-Butyl-5-N-cyclohexylcarboxamido-4-aza-
5ˇ-cholestan-3-one (8b)
M.p.: 186 ◦C. MS m/z (%): 568 (M+, 35.4), 553 (2.9), 444 (100),
166 (38.1), 83 (17.0). 1H NMR: 0.66 (18-H, 3H, s); 0.86 and 0.87
(26-H and 27-H, 3H, d, J = 2.3 Hz); 0.89 (H-21, 3H, d, J = 6.2 Hz);
0.90 (NCH2(CH2)2CH3, 3H, t, J = 7.4 Hz); 1.00 (19-H, 3H, s); 2.43

steroids 7 3 ( 2 0 0 8 ) 1270–1276
1273
(NHCH(CH2)5); 55.7; 56.1; 69.7 (C5); 111.2; 112.7; 119.0; 119.5;
122.0; 122.1; 127.3; 136.3; 172.6 (CONHCH(CH2)5) 173.1 (C3).
Anal. Calcd. for C43H65N3O2: C, 78.73; H, 9.99; N, 6.41. Found:
C, 78.69; H, 10.09; N, 6.62.
0.87 (26-H and 27-H, 3H, d, J = 2.5 Hz); 0.90 (H-21, 3H, d,
J = 6.5 Hz); 1.03 (19-H, 3H, s); 1.29 (NHCH2COOCH2CH3, 3H, t,
J = 7.1 Hz); 2.44 (2-H, 2H, m); 3.21 and 3.45 (NCH2CH2CH2N3,
2H, m, J = 5.3, 10.1 and 13.9 Hz); 3.34 (NCH2CH2CH2N3, 2H,
m); 3.96 and 4.08 (NHCH2COOCH2CH3, 2H, dd, J = 5.6 and
18.9 Hz); 4.21 (NHCH2COOCH2CH3, 2H, q, J = 7.1 Hz); 6.25
(NHCH2COOCH2CH3, 1H, t, J = 5.6 Hz). 13C NMR: 11.9 (C18);
14.1 (NHCH2COOCH2CH3); 18.6 (C21); 19.5 (C19); 21.0; 22.5
and 22.8 (C26 and C27); 23.8; 24.0; 26.7; 27.3; 27.5; 28.0;
27.9 (NCH2CH2CH2N3); 28.2; 28.5 (C2); 34.4; 35.7; 36.0; 39.5;
39.8 (NCH2CH2CH2N3); 38.0 (C10); 41.8 (NHCH2COOCH2CH3);
42.2 (C13); 42.3; 42.7; 49.8 (NCH2CH2CH2N3); 56.1; 56.2; 61.7
(NHCH2COOCH2CH3); 73.2 (C5); 169.6 (CONHCH2COOCH2CH3);
173.2 (C3); 172.6 (CONHCH2COOCH2CH3). Anal. Calcd. for
2.1.14. 4-(2ꢀ-(1H-benzo[b]azol-3-yl)ethyl)-5-N-
cyclohexylcarboxamido-4-aza-5ˇ-cholestan-3-one (10b)
M.p.: 132–134 ◦C. MS m/z (%): 656 (M+, 0.3), 529 (4.5), 476
(51.9), 386 (15.6), 143 (100), 83 (9.5). 1H NMR: 0.67 (18-H, 3H,
s); 0.84 and 0.88 (26-H and 27-H, 3H, d, J = 2.3 Hz); 0.92 (H-
21, 3H, d, J = 6.5 Hz); 1.04 (19-H, 3H, s); 2.49 (2-H, 2H, m);
2.95 and 3.40 (NCH2CH2Ar, 2H, m, J = 5.0 and 12.0 Hz); 3.73
(NHCH(CH2)5, 1H, m); 3.12 and 3.63 (NCH2CH2Ar, 2H, m, J = 4.4
and 12.2 Hz); 5.5 (NHCH(CH2)5, 1H, d J = 7.8 Hz); 7.16 (Ar, 3H,
m); 7.35 (Ar, 1H, m); 7.80 (Ar, 1H, m); 8.09 (Ar, 1H, s). 13C
NMR: 11.9 (C18); 18.6 (C21);; 19.8 (C19); 21.1; 22.5 and 22.8
(C26 and C27); 23.8; 24.0; 24.6; 24.7; 24.8; 25.4; 27.12; 27.4;
27.6; 28.0; 28.2; 28.5 (C2); 32.8; 33.2; 34.4; 35.7; 36.1; 37.8;
39.4; 39.8 (C10); 42.3 (C13); 42.3; 46.1; 48.9 (NHCH(CH2)5);
56.0; 56.1; 73.1 (C5); 111.0; 113.6; 119.3; 119.4; 121.8; 122.0;
127.4; 136.2; 171.0 (C3); 172.8 (CONHCH(CH2)5). Anal. Calcd. for
C43H65N3O2: C, 78.73; H, 9.99; N, 6.41. Found: C, 78.85; H, 10.12;
N, 6.35.
C34H57N5O4: C, 68.08; H, 9.58; N, 11.68. Found: C, 68.12; H, 9.60;
N, 11.67.
2.1.17. 4-Propargyl-5-N-(ethoxycarbonylmethylen)-
carboxamido-4-aza-5˛-cholestan-3-one (12a)
Colorless oil. MS m/z (%): 555 (M+, 0.5), 540 (0.2), 424 (10.0),
102 (14.5), 43 (100). 1H NMR: 0.66 (18-H, 3H, s); 0.85 and 0.87
(26-H and 27-H, 3H, d, J = 2.3 Hz); 0.89 (H-21, 3H, d, J = 6.6 Hz);
0.90 (19-H, 3H, s); 1.27 (NHCH2COOCH2CH3, 3H, t, J = 7.2 Hz);
2.34 (CH2C CH, 2H, t, J = 2.4 Hz); 2.54 (2-H, 2H, m); 3.89 and
3.97 (NHCH2COOCH2CH3, 2H, dd, J = 5.7 and 17.8 Hz); 4.18
(NHCH2COOCH2CH3, 2H, q, J = 7.2 Hz); 4.16 and 4.67 (CH2C CH,
2H, dd, J = 17.8 and 2.4 Hz); 6.91 (NHCH2COOCH2CH3, 1H, t,
J = 5.6 Hz). 13C NMR: 12.1 (C18); 14.1 (NHCH2COOCH2CH3); 16.1
(C19); 18.6 (C21); 22.3; 22.5 and 22.8 (C26 and C27); 23.8; 24.0;
24.2; 26.7; 28.0; 28.9; 29.0 (C2); 29.4; 30.6 (CH2C CH); 34.1;
35.8; 36.0; 39.5; 39.8; 41.5 (NHCH2COOCH2CH3); 42.0 (C10); 42.7
(C13); 46.1; 55.5; 56.0; 61.4 (NHCH2COOCH2CH3); 69.7 (C5); 72.7
(CH2C CH); 80.1 (CH2C CH); 169.5 (CONHCH2COOCH2CH3);
172.8 (C3); 173.8 (CONHCH2COOCH2CH3). Anal. Calcd. for
C34H54N2O4: C, 73.61; H, 9.81; N, 5.05. Found: C, 73.81; H, 9.72;
N, 5.25.
2.1.15. 4-(3ꢀ-Azidopropyl)-5-N-(ethoxycarbonylmethylen)-
carboxamido-4-aza-5˛-cholestan-3-one (11a)
Colorless oil. MS m/z (%): 600 (M+, 0.2), 469 (7.2), 386 (5.2), 258
(2.7), 43 (100). 1H NMR: 0.66 (18-H, 3H, s); 0.85 and 0.86 (26-H
and 27-H, 3H, d, J = 2.3 Hz); 0.89 (H-21, 3H, d, J = 6.5 Hz); 0.89 (19-
H, 3H, s); 1.27 (NHCH2COOCH2CH3, 3H, t, J = 7.0 Hz); 2.03 and
1.72 (NCH2CH2CH2N3, 2H, m); 2.51 (2-H, 2H, m); 3.28 and 3.83
(NCH2CH2CH2N3, 2H, m, J = 5.3, 10.1 and 13.8 Hz); 3.35 and 3.42
(NCH2CH2CH2N3, 2H, m); 3.89 and 3.98 (NHCH2COOCH2CH3,
2H, dd, J = 5.5 and 17.7 Hz); 4.19 (NHCH2COOCH2CH3, 2H, q,
J = 7.0 Hz); 6.41 (NHCH2COOCH2CH3, 1H, t, J = 5.6 Hz). 13C NMR:
12.1 (C18); 14.1 (NHCH2COOCH2CH3); 15.6 (C19); 18.6 (C21); 22.0;
22.5 and 22.8 (C26 and C27); 23.8; 24.0; 26.7; 28.0; 28.2; 28.8;
28.9 (NCH2CH2CH2N3); 29.0 (C2); 33.4; 35.8; 36.1; 39.4; 39.7;
39.9 (NCH2CH2CH2N3); 41.1 (C10); 41.5 (NHCH2COOCH2CH3);
42.6 (C13); 45.4; 49.6 (NCH2CH2CH2N3); 55.6; 56.0; 61.5
(NHCH2COOCH2CH3); 70.0 (C5); 169.6 (CONHCH2COOCH2CH3);
173.2 (C3); 173.9 (CONHCH2COOCH2CH3). Anal. Calcd. for
2.1.18. 4-Propargyl-5-N-(ethoxycarbonylmethylen)-
carboxamido-4-aza-5ˇ-cholestan-3-one (12b)
Colorless oil. MS m/z (%): 555 (M+, 0.4), 540 (0.3), 424 (11.1),
102 (13.7), 43 (100). 1H NMR: 0.67 (18-H, 3H, s); 0.86 and 0.87
(26-H and 27-H, 3H, d, J = 2.2 Hz); 0.89 (H-21, 3H, d, J = 6.5 Hz);
1.05 (19-H, 3H, s); 1.28 (NHCH2COOCH2CH3, 3H, t, J = 7.1 Hz);
2.20 (CH2C CH, 2H, t, J = 2.5 Hz); 2.48 (2-H, 2H, m); 3.90 and
4.10 (NHCH2COOCH2CH3, 2H, dd, J = 5.8 and 17.9 Hz); 4.20
(NHCH2COOCH2CH3, 2H, q, J = 7.1 Hz); 4.15 and 4.22 (CH2C CH,
2H, dd, J = 17.6 and 2.4 Hz); 6.52 (NHCH2COOCH2CH3, 1H, t,
J = 5.4 Hz). 13C NMR: 11.9 (C18); 14.2 (NHCH2COOCH2CH3); 18.6
(C21); 19.4 (C19); 21.0; 22.5 and 22.8 (C26 and C27); 23.8; 24.0;
C34H57N5O4: C, 68.08; H, 9.58; N, 11.68. Found: C, 68.25; H, 9.42;
N, 11.40.
2.1.16. 4-(3ꢀ-Azidopropyl)-5-N-(ethoxycarbonylmethylen)-
carboxamido-4-aza-5ˇ-cholestan-3-one (11b)
Colorless oil. MS m/z (%): 600 (M+, 0.3), 469 (7.9), 386 (6.1),
258 (3.0), 43 (100). 1H NMR: 0.67 (18-H, 3H, s); 0.86 and
Scheme 1 – Synthesis of 4-azacholestanes using an intramolecular Ugi reaction.

1274
steroids 7 3 ( 2 0 0 8 ) 1270–1276
Fig. 2 – (a) Predicted lower energy conformations (B3LYP/6-31G (d,p)) for compound 5b. (b) Diagnostic nOe’s for compound 5b.
26.7; 27.3; 27.6; 28.0; 28.2; 28.4 (C2); 32.8 (CH2C CH); 34.3;
35.7; 36.1; 38.1 (C10); 39.4; 39.7; 41.8 (NHCH2COOCH2CH3); 42.2;
42.3 (C13); 56.0; 56.1; 61.5 (NHCH2COOCH2CH3); 72.0 (C5); 73.4
(CH2C CH); 79.4 (CH2C CH); 169.7 (CONHCH2COOCH2CH3);
172.6 (C3); 172.1 (CONHCH2COOCH2CH3). Anal. Calcd. for
2.1.19. Molecular modeling
A random conformational search of the lowest energy struc-
tures was performed for each model using the Tripos
Molecular Field as implemented in the SYBYL 7.2 software
[9]. The selected conformations were optimized in vacuo at the
B3LYP/6-31G (d,p) level using Gaussian98 [10] and proved to be
local minima via normal mode analysis.
C34H54N2O4: C, 73.61; H, 9.81; N, 5.05. Found: C, 73.55; H, 9.84;
N, 5.12.
Fig. 3 – (a) Predicted lower energy conformations (B3LYP/6-31G (d,p)) for compound 5a. (b) Diagnostic nOe’s for compound 5a.

steroids 7 3 ( 2 0 0 8 ) 1270–1276
1275
Scheme 2 – Possible mechanism of the intramolecular Ugi reaction leading to 4-azasteroids.
which can be assigned to H-7␣. The proposed theoretical
model shows that this proton might be affected by the
anisotropic influence of the aromatic ring, confirming the C-5
stereochemistry (Fig. 2).
In the same way, Fig. 3a shows two of the predicted
lower energy conformations for compound 5a, which might
account for the observed correlations in the NOESY spectrum
(Fig. 2b).
There are several proposals on the U-4CR mechanism [11].
Scheme 2 depicts the possible mechanism that may be work-
ing in this case, and involves the formation of an iminium
ion 13, which gives an addition onto the carbenoid carbon of
the isocyanide. The adduct (14a or 14b) rearranges to the final
products.
Table 1 shows that when aniline was used as the amino
component, the reaction failed. It is thought that, although
anilines react to give the imine readily (Scheme 2), the con-
centration of the corresponding iminium ion 13 is low, due
to the electron withdrawing effect of the aromatic ring, thus
preventing the reaction to proceed [11].
3.
Results and discussion
The synthesis of the novel 4-azasteroids is shown in Scheme 1.
The oxoacid 4 was obtained from cholesterol following a stan-
dard procedure [8].
This intermediate compound contains both a carboxylic
group and a keto group. Thus, the U-4CR with an amine and an
isonitrile led to a mixture of the epimeric 4-azasteroids 5a–12a
and 5b–12b. The reaction generally took place smoothly in
boiling methanol or ethanol in good yields (45–77% of both
isomers).
The stereochemistry at C-5 for each pair of isomers
was established from both NOESY experiments and theo-
retical molecular models. Figs. 2 and 3 show the results
obtained following this approach for compounds 5a and
5b.
The nOe’s between diagnostic proton resonances, which
were completely assigned using 1D and 2D NMR experiments,
were determined.
On the other hand, the low nucleophilicity of the tert-
butylamine might explain that the U-4CR also failed when this
amine was employed.
On the other hand, the structures having the lower ener-
gies, found after a systematic conformational search, were
optimized.
Except for the aforementioned components, the reaction
worked well with a set of structurally diverse amines, which
can also include additional functional groups (Table 1), gener-
ating a family of novel N-substituted 4-azasteroids.
The most notable feature of this synthetic approach is
that it allows the facile introduction of a polyfunctionalized
chain at C-5, an important task not reported previously. The
structural variety of this side chain depends on the selected
isonitrile.
For example, the analysis of compound 5b predicts the
existence of several minima. Given the rigidity of the steroidal
frame, these conformers differ mainly in the relative position
of the substituents at N-4 and C-5. It is interesting to note
that, in all of the predicted conformations, the benzyl moi-
ety lies under the plane defined by the steroid rings. Fig. 2a
depicts two of the most stable conformations. Fig. 2b shows a
simplified model for each conformation in which the pairs of
protons having correlations in the NOESY spectrum are indi-
cated.
As expected for the U-4CR, a low stereoselectivity was
observed [12]. Nevertheless, when a bulky isonitrile was used,
such as in the synthesis of compounds 6a and 6b, a high ratio
Furthermore, the 1H NMR spectrum of compound 5b has a
resonance with a remarkable low chemical shift at 0.40 ppm,

1276
steroids 7 3 ( 2 0 0 8 ) 1270–1276
Table 1 – Yields of compounds 5–12
Amine R1-NH2 Isonitrile R2-NC
Acknowledgements
Yielda
This work was supported by grants from the Universidad de
Buenos Aires (UBACyT X-190) and the Agencia Nacional de Pro-
moción Científica y Técnica (ANPCyT PICT 38285/05). We are
grateful to UMYMFOR (UBA-CONICET) for the analytical and
spectroscopic determinations.
63.3% (5a/5b 2.8:1)
45.7% (6a/6b 20:1)
r e f e r e n c e s
70.2% (7a/7b 1.6:1)
66.0% (8a/8b 1.5:1)
[1] Morzycki JW, Wawer I, Gryszkiewicz A, Maj J, Siergiejczyk L,
Zaworska A. 13C-NMR study of 4-azasteroids in solution and
solid state. Steroids 2002;67:621–6.
[2] Rasmusson GH, Reynolds GF, Steinberg NG, Walton E, Patel
GF, Liang T, et al. Azasteroids: structure–activity
relationships for inhibition of 5␣-reductase, and of androgen
receptor binding. J Med Chem 1986;29:2298–315.
[3] Burbiel J, Bracher F. Azasteroids as antifungal. Steroids
2003;68:587–94.
62.7% (9a/9b 1.4:1)
[4] Zhu J, Bienyamé H. Multicomponet reactions. Weinheim:
Wiley-VCH Verlag GmbH & Co.; 2005.
[5] Dömling A. Recent developments in isocyanide based
multicomponent reactions in applied chemistry. Chem Rev
2006;106:17–89.
77.7% (10a/10b 1.7:1)
No reaction
[6] Marcaccini S, Pepino R, Torroba T, Miguel D, García-Valverde
M. Synthesis of thiomorpholines by an intramolecular Ugi
reaction. Tetrahedron Lett 2002;43:8591–3.
[7] Sung K, Wu S-H, Chen P-I. Facile two-pot syntheses of novel
alternating benzene/imidazole systems. Tetrahedron
2002;58:5599–602.
No reaction
[8] Edward JT, Holder D, Lunn WH, Puskas I. Oxidation of
cholest-4-en-3-one with periodate–permanganate. Can J
Chem 1961;39:599–600.
[9] SYBYL 7.3, Tripos International, 1699 South Hanley Rd., St.
Louis, MO 63144, USA.
68.3% (11a/11b 2.9:1)
68.4% (12a/12b 1.9:1)
[10] Frisch MJ, Trucks GW, Schlegel HB, Scuseria GE, Robb MA,
Cheeseman JR, Zakrzewski VG, Montgomery JA, Stratmann
Jr RE, Burant JC, Dapprich S, Millam JM, Daniels AD, Kudin
KN, Strain MC, Farkas O, Tomasi J, Barone V, Cossi M, Cammi
R, Mennucci B, Pomelli C, Adamo C, Clifford S, Ochterski J,
Petersson GA, Ayala PY, Cui Q, Morokuma K, Malick DK,
Rabuck AD, Raghavachari K, Foresman JB, Cioslowski J, Ortiz
JV, Baboul AG, Stefanov BB, Liu G, Liashenko A, Piskorz P,
Komaromi I, Gomperts R, Martin RL, Fox DJ, Keith T,
Al-Laham MA, Peng CY, Nanayakkara A, Gonzalez C,
Challacombe C, Gill PMW, Johnson BG, Chen W, Wong MW,
Andres JL, Head-Gordon M, Replogle ES, Pople JA. Gaussian
98 (Revision A.7). Pittsburgh, PA: Gaussian, Inc.; 1998.
[11] Marcaccini S, Torroba T. The use of the Ugi four-component
condensation. Nat Protocols 2007;2:632–9.
a
Isolated yields.
of the product with a trans A/B ring junction was obtained,
suggesting that in this case the attack on the ␣-face might be
highly favored.
In order to explore the feasibility and scope of this syn-
thetic methodology, in this work we used cholesterol as the
starting material, and in sight of our results we suggest that
this approach could be applied to other steroids with the con-
venient structures, targeted to find new biologically active
compounds.
[12] Banfi L, Basso A, Guanti G, Riva R. Assymetric
isocyanide-based MCRs. In: Zhu J, Bienyamé H, editors.
Multicomponet reactions. Weinheim: Wiley-VCH Verlag
GmbH & Co.; 2005.
Further studies are under way both to expand this proce-
dure to steroids other than cholestanes and to evaluate the
biological properties of the new compounds.