Synthesis of new steroidal derivatives by the reaction of steroid-amino acid conjugates with N,N′-dicyclohexyl-carbodiimide. Unusual formation of steroidal imide derivatives

Article abstract of DOI:10.1016/j.tet.2009.04.036

Several new steroid derivatives have been synthesised by the reaction of steroid-amino acid conjugates with N,N′-dicyclohexyl-carbodiimide. Selectivity of the reaction was found to depend greatly on the properties of the amino acid moiety. While the react

Full text of DOI:10.1016/j.tet.2009.04.036

Tetrahedron 65 (2009) 4659–4663
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis of new steroidal derivatives by the reaction of steroid–amino acid
conjugates with N,N0-dicyclohexyl-carbodiimide. Unusual formation
of steroidal imide derivatives
a
b
c
c
b
a,
*
´
´
´
´
´
´
´
´
¨
Eszter Takacs , Zoltan Berente , Viktor Hada , Sandor Maho , Laszlo Kollar , Rita Skoda-Foldes
a University of Pannonia, Institute of Chemistry, Department of Organic Chemistry, H-8201 Veszpre´m, PO Box 158, Hungary
b University of P´ecs, Department of Inorganic Chemistry, H-7624 Pe´cs, PO Box 266, Hungary
c Chemical Works of Gedeon Richter Ltd, Budapest, Hungary
a r t i c l e i n f o
a b s t r a c t
Article history:
Several new steroid derivatives have been synthesised by the reaction of steroid–amino acid conjugates
with N,N0-dicyclohexyl-carbodiimide. Selectivity of the reaction was found to depend greatly on the
properties of the amino acid moiety. While the reaction of the glycine derivative led to the corresponding
5(4H)-oxazolone, an unusual imide formation together with an N-acylurea side product was observed in
Received 15 January 2009
Received in revised form 27 March 2009
Accepted 9 April 2009
Available online 17 April 2009
the case of conjugates of L-alanine, L-phenylalanine and L-methionine. The structures of the new prod-
ucts, steroidal imide and N-acylurea derivatives, were determined by various spectroscopic methods.
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Steroids
Amino acids
Imides
DCC
1. Introduction
activating agent. This method had been used successfully by Beck
and co-workers for the synthesis of various ferrocenyl-oxazolones.4
Several steroids with heterocylic moieties (e.g., imidazolyl,
pyridyl, pyrazolyl, isoxazolyl, thiazolyl and oxazolyl) on C-17 show
interesting biological properties and can be used as inhibitors of
2. Results and discussion
17a
-hydroxylase-C17,20-lyase1 but until now there are no examples
The starting steroid–amino acid conjugates (1a–4a) were
of the syntheses of steroidal 5(4H)-oxazolone derivatives.
obtained as described previously,6 by palladium-catalysed amino-
5(4H)-Oxazolones2 are known to be produced easily from N-acyl
amino acid derivatives with dehydrating agents like activated an-
hydrides3 or carbodiimides.4 At the same time the oxazolone ring
system contains numerous reactive sites and undergoes a number
of reactions such as acylation, alkylation, arylation, etc.5 In addition,
carbonylation of 17-iodo-5a-androst-16-ene using amino acid es-
ters as N-nucleophiles. Hydrolysis of methyl esters 1a–4a under
basic conditions led to the carboxylic acid products 1b–4b in high
yields (Scheme 1).
Carboxylic acids 1b–4b were reacted with DCC under the condi-
tionsreported by Beck and co-workersfor the synthesis of ferrocenyl-
oxazolones.4 However, only reaction of 1b with DCC resulted in the
formation of the expected 5(4H)-oxazolone derivative 1c in good
yield (Scheme 2, Table 1, entry 1). It should be noted that 1c is very
sensitive to hydrolysis in solution and decomposes giving 1b after
a few days.
At the same time, only traces of compounds of similar structure
2c and 4c could be detected by GC–MS7 in the reaction mixtures of
DCC and acids 2b and 4b, respectively, and no formation of an
oxazolone derivative was observed starting from 3b. Instead, two
compounds of very different structure were isolated from these
reaction mixtures that were proved to be imides 2d–4d and
N-acylurea derivatives 2e–4e (Scheme 2, entries 2–4).
they can be used for the synthesis of oxazoles, b-lactams, pyrroles,
pyrrolines, imidazoles and imidazolines, so they also serve as useful
intermediates.5
Recently, we reported a high-yielding synthesis of new steroid
amino acid ester conjugates via palladium-catalysed amino-
carbonylation of 17-iodo-5a-androst-16-ene in the presence of
amino acid esters as nucleophiles.6 Based on these studies we de-
cided to investigate the possibility of the synthesis of new steroidal
5(4H)-oxazolone derivatives starting from the hydrolysis products
of esters 1a–4a using N,N0-dicyclohexyl-carbodiimide (DCC) as the
* Corresponding author. Tel.: þ36 88 624719; fax: þ36 88 624469.
E-mail address: skodane@almos.uni-pannon.hu (R. Skoda-Fo¨ldes).
0040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.04.036

´
E. Takacs et al. / Tetrahedron 65 (2009) 4659–4663
4660
O
O
H
N
H
N
1. NaOH, EtOH, H2O
2. HCl
CO2H
CO2Me
R
R
1a R=H
1b R=H
(93 %)
2a R=Me
H
2b R=Me
(91 %)
(86%)
3a R=CH2Ph
4a R=(CH2)2SCH3
3b R=CH2Ph
4b R=(CH2)2SCH3 (84 %)
Scheme 1. Synthesis of steroid–amino acid conjugates 1b–4b.
Scheme 2. Reaction of steroid–amino acid conjugates 1b–4b with DCC.
Formation of the latter compounds is not surprising as carboxylic
acids are known to react with carbodiimides such as DCC to give
N-acylureas via an O-acyl/N-acyl rearrangement reaction of the
O-acylisourea type active esters.8 Although the high reactivity of the
O-acylisourea intermediates is reported to provoke racemisation in
some cases, the N-acylurea derivatives 2e–4e were isolated as single
isomers.
to the best of our knowledge, no imide derivatives were isolated from
reaction mixtures of amino acid derivatives and DCC. Our experi-
ments show that in some cases, the possibility of the formation of
imide-type side products should be taken into consideration.10
At the same time, unsymmetrical acyclic imides represent a very
important group of compounds as they usually show high bi-
ological (e.g., antimicrobial or antifungal) activity. This structural
motif also appears in certain natural products such as fumar-
amidmycin11 or coniothyriomycin.12 In the past two decades, design
of bioconjugates consisting of two entities having different bi-
ological activities has been receiving increasing attention. Among
the hybrid natural products, hybrids of steroid frameworks have
attracted great attention due to the significant biological properties
and numerous therapeutic effects of steroids.13 The reaction of
steroidal amino acids with DCC leading to steroidal imides pre-
sented here can be an important addition to the already known
synthetic methods of producing steroid conjugates.
However, the formation of imides was completely unexpected.
Although unsymmetrical imides have been produced by oxidative
decarboxylation of N-acyl amino acids9 induced by Agþ/Cu2þ/S2O28ꢀ
,
Table 1
The effect of the reaction conditions on product distribution of reactions of 1b–4b
with DCC
Entry
Substrate
Methoda
Yields of steroid derivatives (%)
c
d
e
bb
1
2
3
4
5
6
7
8
1b
2b
3b
4b
2b
3b
2b
3b
4b
2b
4b
2b
3b
4b
2b
2b
3b
4b
A
A
A
A
B
B
C
C
C
D
D
E
E
E
F
G
G
G
91
dc
d
dc
d
d
d
d
d
dc
dc
d
d
d
d
d
d
d
d
35
61
42
28
30
9
16
17
9
d
36
26
35
40
42
10
13
8
68
72
32
43
37
38
25
26
23
2
5
5
In order to obtain a better insight into the reaction, the distri-
bution of products 2d–4d/2e–4e was investigated using various
reaction conditions (Table 1).
6
Temperature is known to have a decisive effect on the outcome
of the reaction: at lower temperatures the formation of O-acyli-
sourea and oxazolone derivatives is favoured, while an increase in
the temperature usually leads to N-acylurea-type products in
higher yields.8b,d In our case, stirring the reaction mixtures at 40 ꢁC
instead of rt resulted in a slight decrease in the amount of the imide
derivatives 2d and 3d, and an increase in the yield of N-acylurea
products 2e and 3e (Table 1, entries 5 and 6). No formation of
oxazolones could be detected. Lowering the temperature resulted
only in a decrease in the reaction rate and an increase in the
amount of recovered starting material (entries 7–9).
11
12
70
65
67
3
9
10
11
12
13
14
15
16
17
18
7
5
d
d
d
42
15
17
11
62
51
56
4
51
56
54
It was proved that product distribution was greatly influenced
by both light and air. The effect of light was demonstrated by car-
rying out the reactions of 2b and 4b while protecting the reaction
mixture from light (Table 1, entries 10 and 11). The amount of the
steroidal imide derivatives 2d and 4d was decreased dramatically,
while the yield of 2e and 4e increased. At the same time, the
presence of 5(4H)-oxazolones 2c and 4c was detected again by GC–
MS. The use of inert atmosphere prevented imide formation com-
pletely. At the same time, it led to an increase in the amount of the
recovered starting material, thus lowering the reaction rate. On the
contrary, when oxygen was bubbled through the reaction mixture,
a
DCC was added dropwise at 0 ꢁC in CH2Cl2 to the solution of the substrate over
1 h. Method A: after addition of DCC, the mixture was stirred for 7 h at rt. Method B:
after addition of DCC, the mixture was stirred for 7 h at 40 ꢁC. Method C: after ad-
dition of DCC, the mixture was stirred for 7 h at 0 ꢁC. Method D: the reaction was
carried out according to method A by protecting from light. Method E: the reaction
was carried out according to method A in an inert atmosphere. Method F: the re-
action was carried out according to method A but oxygen was bubbled through the
reaction mixture. Method G: the reaction was carried out according to method A in
the presence of Pd/C (10 w/w% Pd) (2b–4b/DCC/Pd¼1:1:0.05).
b
Substrate recovered.
c
The presence of the corresponding 5(4H)-oxazolone could be detected by
GC–MS in the reaction mixture.7

´
E. Takacs et al. / Tetrahedron 65 (2009) 4659–4663
4661
a slight increase in the yield of the imide derivative 2d was ob-
served (compare entries 2 and 15).
relative to CHCl3 (7.26 and 77.00 ppm for 1H and 13C, respectively).
Mass spectra of 1c and 3d were recorded on an HP-5971A MSD
connected to an HP-5890/II gas chromatograph. MS measurements
of 1b, 2d and 2e were carried out on a Finnigan MAT95 SQ mass
spectrometer using FIB ionisation (Cs ion, glycerine matrix, 20 kV)
for compound 1b, and EI ionisation technique (70 eV, 220 ꢁC source
temperature) for compounds 2d and 2e. High-resolution MS mea-
surements of 2b, 3b, 4b, 4d, 3e and 4e were carried out on a Thermo
LTQ FT Ultra mass spectrometer (ESI, 4.0 kV spray voltage, 295 ꢁC
capillary temperature, solvent: MeOH/H2O 1:1þ1 v/v % cc. AcOH).
The protonated molecular ion peaks were fragmented by CID at
a normalised collision energy of 10–14%. The relative abundance
values of the fragment ions in the MS–MS spectrum are given in
brackets. IR spectra were made using an Avatar 330 FT-IR in-
strument. Samples were prepared as KBr pellets. Elemental analy-
ses were measured on a 1108 Carlo Erba apparatus.
Under UV irradiation and in air 5(4H)-oxazolones were reported
to go through oxidative photodecarboxylation and to decompose to
unsymmetrical acyclic imides through an endoperoxide in-
termediate.14 Although a certain explanation for the formation of
steroidal imide derivatives 2d–4d under our conditions cannot be
given, it is possible that a similar reaction takes place (Scheme 3).
This is supported by the fact that both the use of inert atmosphere
and protection of the reaction mixtures from light led to a marked
decrease in the yields of imide products.
Although N-acylureas are known to be unreactive, the possi-
bility of transforming 2e–4e to 2d–4d was investigated, too.
However, besides the starting material no other steroid derivatives
could be detected in the reaction mixtures of 2e–4e and DCC under
the same conditions given in entries 1–4, Table 1.
5(4H)-Oxazolones were reported to be converted to imides via
Pd/C-catalyzed oxidation and decarboxylation by Bates and co-
workers,15 so the reactions of 2b–4b with DCC were carried out in
the presence of Pd/C (entries 16–18). Unfortunately, the yield of
imides 2d–4d could not be increased even in the presence of the
catalyst.
Methyl esters 1a–4a were obtained as described previously.6a
4.2. General procedure for the synthesis of steroid–amino
acid conjugates (1b–4b)
The steroidal amino acid ester (1a–4a, 0.5 mmol) was dissolved
in ethanol (15 mL) and then a slight excess of 0.1 M NaOH (30 mL)
was added dropwise at 0 ꢁC. The solution was stirred for 7 h at rt
and an equimolar amount of 0.1 M HCl (to the amount of NaOH)
was added dropwise. The mixture was extracted with CH2Cl2
(3ꢂ50 mL). The combined organic phases were dried over Na2SO4
and the solvent was removed by rotary evaporation. The products
were purified by column chromatography (silica gel, chloroform/
MeOH¼8:2).
3. Conclusions
In conclusion it can be stated that either a new steroidal 5(4H)-
oxazolone (1c) or new steroidal N-acylureas (2e–4e) and imide
derivatives (2d–4d) can be obtained in moderate to good yields by
the reaction of steroid–amino acid conjugates with DCC. Although
oxazolone 1c could be produced in excellent yield from the glycine
derivative 1b, the use of other steroidal carboxylic acids (2b–4b) led
to the formation of mixtures of N-acylureas 2e–4e and imides 2d–
4d. Formation of imide derivatives can be explained by spontane-
ous oxidative decarboxylation of the primarily formed oxazolone
derivatives 2c–4c.
Although oxidative decarboxylation of 5(4H)-oxazolones in the
presence of oxidising agents or under UV irradiation is a known
process, the spontaneous reaction of N-acyl amino acids and DCC
leading to imides or decarboxylation of oxazolones without the use
of any inducers is unprecedented.
4.3. General procedures for the reactions of 1b–4b with
dicyclohexyl-carbodiimide (DCC)
Method A. The steroid–amino acid conjugate (1b–4b, 0.3 mmol)
was suspended in CH2Cl2 (6 mL). At 0 ꢁC a solution of an equimolar
amount of DCC (0.3 mmol) in CH2Cl2 (3 mL) was added dropwise in
1 h. After 7 h stirring at rt, the solvent was removed by rotary
evaporation. The products were purified by column chromatogra-
phy (silica gel, n-hexane/EtOAc¼8:2).
The reactivity of N-acyl amino acids is known to depend greatly
on both the choice of the N-acyl group, in our case the steroid
moiety, and the type of the amino acid itself. This could be the
reason for the unique behaviour of 2b–4b.
Method B. The steroid–amino acid conjugate (2b or 3b, 0.3 mmol)
was suspended in CH2Cl2 (6 mL). At 0 ꢁC a solution of an equimolar
amount of DCC (0.3 mmol) in CH2Cl2 (3 mL) was added dropwise in
1 h. After 7 h stirring at 40 ꢁC, the solvent was removed by rotary
evaporation. The products were purified by column chromatography
(silica gel, n-hexane/EtOAc¼8:2).
4. Experimental
Method C. The steroid–amino acid conjugate (2b–4b, 0.3 mmol)
was suspended in CH2Cl2 (6 mL). At 0 ꢁC a solution of an equimolar
amount of DCC (0.3 mmol) in CH2Cl2 (3 mL) was added dropwise in
1 h. After 7 h stirring at 0 ꢁC, the solvent was removed by rotary
evaporation. The products were purified by column chromatogra-
phy (silica gel, n-hexane/EtOAc¼8:2).
4.1. General procedures
1H and 13C NMR spectra were recorded in CDCl3 on a Varian
Inova 400 spectrometer at 400.13 MHz and 100.62 MHz, re-
spectively. Chemical shifts
d are reported in parts per million
Scheme 3. Possible mechanism for the formation of imides 2d–4d.

´
E. Takacs et al. / Tetrahedron 65 (2009) 4659–4663
4662
Method D. Same as method A but addition of the DCC solution
(100.62 MHz, CDCl3): 176.0, 160.7, 142.7, 141.8, 56.9, 55.2, 54.8, 47.3,
46.4, 38.4, 36.5, 34.9, 33.9, 32.3, 32.0, 29.0, 28.9, 26.8, 22.1, 20.6,16.1,
12.1. IR (KBr, cmꢀ1): 1826,1650,1627. MS m/z 341 (25) (Mþ), 326 (8),
284 (31), 269 (28), 257 (9), 178 (14), 148 (10), 121 (24), 105 (35), 91
(54), 67 (87), 55 (100). Analysis calculated for C22H31NO2: C, 77.38;
H, 9.15; N, 4.10. Found: C, 77.65; H, 8.95; N, 3.86. White solid, mp
132–134 ꢁC. Isolated yield: 91% (method A).
and stirring at rt was carried out by preventing from light.
Method E. Same as method A but addition of the DCC solution
and stirring at rt was carried out in an argon atmosphere.
Method F. Same as method A but oxygen was bubbled through
the mixture throughout the reaction.
Method G. The steroid–amino acid conjugate (2b–4b, 0.3 mmol)
and 15 mg Pd/C (10 w/w % Pd) were suspended in CH2Cl2 (6 mL). At
0 ꢁC a solution of an equimolar amount of DCC (0.3 mmol) in CH2Cl2
(3 mL) was added dropwise in 1 h. After 7 h stirring at rt, the sol-
vent was removed by rotary evaporation. The products were puri-
fied by column chromatography (silica gel, n-hexane/EtOAc¼8:2).
4.4.6. 17-(N-Acetyl-carbamoyl)-androst-16-ene (2d)
dH (400.13 MHz, CDCl3): 8.16 (br s, 1H), 6.51–6.55 (m, 1H), 2.50
(s, 3H), 0.70–2.40 (m, 22H, ring protons), 0.97 (s, 3H), 0.81 (s, 3H). dC
(100.62 MHz, CDCl3): 173.1, 163.5, 150.1, 140.9, 56.7, 55.3, 47.5, 47.2,
38.7, 36.7, 34.8, 34.0, 32.4, 32.1, 29.2, 29.0, 27.0, 25.5, 22.3, 20.8, 16.5,
12.4. IR (KBr, cmꢀ1): 3284, 1711, 1689, 1591. MS m/z (rel int. %): 343
(3) (Mþ), 328 (12), 284 (100), 269 (87), 257 (24), 241 (5), 161 (6), 147
(7), 121 (9), 105 (8), 91 (8), 43 (10). Analysis calculated for
C22H33NO2: C, 76.92; H, 9.68; N, 4.08. Found: C, 76.95; H, 9.47; N,
4.24. White solid, mp 151–153 ꢁC. Isolated yield: 35% (method A).
4.4. Characterisation of the products
4.4.1. N-(17-Androst-16-enoyl)-glycine (1b)
dH (400.13 MHz, CDCl3): 6.50 (br s, 1H), 6.42 (br s, 1H), 6.05 (br s,
1HþH2O (solvent)), 4.10 (br s, 2H), 0.60–2.20 (m, 22H, ring protons),
0.95 (s, 3H), 0.78 (s, 3H). dC (100.62 MHz, CDCl3): 179.2, 166.7, 149.8,
138.1, 57.0, 55.3, 47.5, 46.7, 42.1, 38.7, 36.7, 35.2, 34.0, 32.1, 31.9, 29.2,
29.1, 27.0, 22.4, 20.9, 16.7, 12.4. IR (KBr, cmꢀ1): 3391, 1732, 1646, 1587.
MS: MþH: m/z 360, MS–MS of m/z 360: m/z 285 (100), 257 (3).
Analysis calculated for C22H33NO3 C, 73.50; H, 9.25; N, 3.90. Found: C,
73.64;H, 9.27;N, 3.96.Whitesolid,mp155–156 ꢁC.Isolatedyield:93%.
4.4.7. 17-(N-(Phenyl-acetyl)-carbamoyl)-androst-16-ene (3d)
dH (400.13 MHz, CDCl3): 8.01 (br s,1H), 7.15–7.40 (m, 5H), 6.45 (s,
1H), 4.18 (s, 2H), 0.80–2.34 (m, 22H, ring protons), 0.96 (s, 3H), 0.81
(s, 3H). dC (100.62 MHz, CDCl3): 172.9, 163.0, 149.9, 140.7, 133.8,
129.8, 128.6, 127.1, 56.5, 55.1, 47.2, 47.0, 43.7, 38.4, 36.5, 34.6, 33.8,
32.2, 31.9, 29.0, 28.8, 26.8, 22.1, 20.6, 16.3,12.2. IR (KBr, cmꢀ1): 3326,
1710, 1638, 1589. MS m/z 419 (43) (Mþ), 376 (100), 348 (12), 257
(10), 217 (31), 144 (62), 118 (47), 91 (54), 67 (33). Analysis calculated
for C28H37NO2: C, 80.15; H, 8.89; N, 3.34. Found: C, 80.02; H, 8.98; N,
3.51. White solid, mp 144–145 ꢁC. Isolated yield: 61% (method A).
4.4.2. N-(17-Androst-16-enoyl)-alanine (2b)
dH (400.13 MHz, CDCl3/DMSO-d6 1:1): 7.15–7.22 (m, 1H), 6.22–
6.29 (m, 1H), 3.95 (br s, 1H), 3.39 (br s, 1HþH2O (solvent)), 1.24 (d, J
6.7 Hz, 3H), 0.63–2.20 (m, 22H, ring protons), 0.88 (s, 3H), 0.76 (s, 3H).
dC (100.62 MHz, CDCl3/DMSO-d6 1:1): 182.6, 163.7, 150.6, 134.1, 56.3,
54.5, 46.6, 45.8, 45.4, 37.9, 35.9, 34.5, 33.3, 31.4, 30.9, 28.5, 28.4, 26.2,
21.6, 20.2,19.0,16.1,11.8. IR (KBr, cmꢀ1): 3417,1736,1636,1589. HRMS
MþH: m/z 374.26846, calculated value for C23H36NO3: 374.26897
(delta: ꢀ1.36 ppm). MS–MS of m/z 374: m/z 285. Analysis calculated
for C23H35NO3: C, 73.96; H, 9.44; N, 3.75. Found: C, 74.18; H, 9.47; N,
3.88. White solid, mp 176–178 ꢁC. Isolated yield: 91%.
4.4.8. 17-(N-(3-Methyl-thio-propionyl)-carbamoyl)-
androst-16-ene (4d)
dH (400.13 MHz, CDCl3): 8.06 (br s, 1H), 6.49–6.51 (m, 1H), 2.80
(t, J 7.1 Hz, 2H), 2.13 (s, 3H), 0.80–2.35 (m, 24H ring pro-
tonsþCH2CH2S), 0.91 (s, 3H), 0.80 (s, 3H). dC (100.62 MHz, CDCl3):
173.7, 163.1, 149.8, 140.7, 56.4, 55.0, 47.2, 46.9, 38.4, 37.5, 36.4, 34.5,
33.7, 32.2, 31.8, 28.9, 28.8, 28.3, 26.7, 22.0, 20.5, 16.2, 15.6, 12.1. IR
(KBr, cmꢀ1): 3325, 1711, 1626, 1573. HRMS: MþH: m/z 404.26113,
calculated value for C24H38NO2S: 404.26178 (delta: ꢀ1.60 ppm).
MS–MS of m/z 404: m/z 356 (6), 285 (100), 257 (2). Analysis cal-
culated for C24H37NO2S: C, 71.42; H, 9.24; N, 3.47. Found: C, 71.62;
H, 9.01; N, 3.61. White solid, mp 132–134 ꢁC. Isolated yield: 42%
(method A).
4.4.3. N-(17-Androst-16-enoyl)-phenylalanine (3b)
dH (400.13 MHz, CDCl3): 7.00–7.20 (m, 5H), 6.51 (br s, 1H), 6.08–
6.13 (m, 1H), 4.45–4.55 (m, 1H), 3.60 (br s, 1HþH2O (solvent)), 3.18–
3.30 (m, 1H), 2.94–3.07 (m, 1H), 0.50–1.96 (m, 22H, ring protons),
0.70 (s, 6H). dC (100.62 MHz, CDCl3): 178.9,166.5,149.8,138.3,136.9,
129.4, 128.1, 126.1, 56.5, 54.9, 51.9, 47.1, 46.1, 38.4, 37.5, 36.3, 34.6,
33.6, 31.8, 31.5, 29.0, 28.8, 26.7, 22.1, 20.6, 16.3, 12.0. IR (KBr, cmꢀ1):
3419, 1708, 1642, 1602. HRMS MþH: m/z 450.30011, calculated
value for C29H40NO3: 450.30027 (delta: ꢀ0.36 ppm). MS–MS of m/z
450: m/z 432 (5), 404 (3), 285 (100). Analysis calculated for
C29H39NO3: C, 77.47; H, 8.74; N, 3.12. Found: C, 77.67; H, 8.80; N,
3.22. White solid, mp 158–160 ꢁC. Isolated yield: 86%.
4.4.9. N,N0-Dicyclohexyl-N0-(2-(5
carboxamido)-propionyl)-urea (2e)
a-androst-16-ene-17-
dH (400.13 MHz, CDCl3): 7.50–7.62 (m,1H), 6.39–6.43 (m,1H), 6.06
(d, J 6.7 Hz, 1H), 4.67 (qui, J 6.7 Hz, 1H), 4.05–4.15 (m, 1H), 3.60–3.70
(m, 1H), 1.33 (d, J 6.7 Hz, 3H), 0.70–2.20 (m, 42H, steroidal ring pro-
c
tonsþ Hex ring protons), 0.94 (s, 3H), 0.79 (s, 3H). dC (100.62 MHz,
4.4.4. N-(17-Androst-16-enoyl)-methionine (4b)
CDCl3):171.8,166.4,153.5,149.5,137.9, 56.8, 55.0, 54.8, 50.3, 48.0, 47.2,
46.4, 38.4, 36.4, 35.0, 33.8, 32.6, 31.8, 31.7, 31.6, 31.4, 29.3, 29.0, 28.8,
26.7, 26.0, 25.9, 25.4, 25.3, 24.8 (2C), 22.1, 20.6,18.5,16.4,12.1. IR (KBr,
cmꢀ1): 3399, 1703, 1646, 1593. MS m/z 579 (0.04) (Mþ), 454 (7), 411
(9), 356 (6), 329 (100), 314 (31), 285 (89), 257 (5). Analysis calculated
for C36H57N3O3: C, 74.57; H, 9.91; N, 7.25. Found: C, 74.78; H, 9.72; N,
7.41. White solid, mp 150–151 ꢁC. Isolated yield: 68% (method D).
dH (400.13 MHz, CDCl3): 7.02 (br s, 1H), 6.43 (br s, 1H), 4.12–4.29
(m, 1H), 2.79 (br s, 1H), 2.39–2.53 (m, 2H), 2.03 (s, 3H), 0.7–2.20 (m,
24H, ring protonsþCH2CH2S), 0.90 (s, 3H), 0.79 (s, 3H). dC
(100.62 MHz, CDCl3): 174.7, 166.5, 149.9, 138.4, 57.0, 55.3, 52.1, 47.4,
46.7, 38.7, 36.7, 35.2, 34.0, 32.1, 31.9, 31.7, 30.3, 29.2, 29.1, 27.0, 22.3,
20.9, 16.8, 15.7, 12.4. IR (KBr, cmꢀ1): 3396, 1712, 1653, 1593. HRMS
MþH: m/z 434.27187, calculated value for C25H40NO3S: 434.27234
(delta: ꢀ1.09 ppm). MS–MS of m/z 434: m/z 416 (13), 386 (5), 285
(100). Analysis calculated for C25H39NO3S: C, 69.24; H, 9.06; N, 3.23.
Found: C, 69.42; H, 9.11; N, 3.15. White solid, mp 149–150 ꢁC. Iso-
lated yield: 84%.
4.4.10. N,N0-Dicyclohexyl-N0-(2-(5
a-androst-16-ene-17-
carboxamido)-3-phenyl-propionyl)-urea (3e)
dH (400.13 MHz, CDCl3): 7.36 (d, J 7.9 Hz, 1H), 7.00–7.30 (m, 5H),
6.28–6.35 (m, 1H), 5.95–6.05 (m, 1H), 4.82–4.93 (m, 1H), 4.05–4.17
(m,1H), 3.59–3.73 (m,1H), 3.10 (dd, J 5.7,13.6 Hz,1H), 2.90 (dd, J 9.5,
c
4.4.5. 2-(Androst-16-ene-17-yl)-5(4H)-oxazolone (1c)
dH (400.13 MHz, CDCl3): 6.61–6.68 (m, 1H), 4.25 (s, 2H), 0.72–
2.40 (m, 22H, ring protons), 0.92 (s, 3H), 0.80 (s, 3H). dC
13.6 Hz, 1H), 0.70–2.20 (m, 42H, steroidal ring protonsþ Hex ring
protons), 0.92 (s, 3H), 0.78 (s, 3H). dC (100.62 MHz, CDCl3): 172.1,
166.2, 153.2, 149.4, 138.2, 136.1, 129.1, 128.7, 127.1, 56.7, 55.0, 53.5,

´
E. Takacs et al. / Tetrahedron 65 (2009) 4659–4663
4663
2. Mukerjee, A. K. Heterocycles 1987, 26, 1077–1097.
3. (a) VandenBerg, G. E.; Harrison, J. B.; Carter, H. E.; Magerlein, B. J. Org. Synth.
1973, 5, 946–948; (b) Ko´cza´n, G.; Csı´k, G.; Csa´mpai, A.; Balog, E.; Bosze, S.;
53.3, 50.3, 47.2, 46.2, 38.7, 38.4, 36.4, 34.9, 33.7, 32.5, 31.8, 31.6, 31.5,
31.4, 29.3, 29.0, 28.8, 26.7, 26.0, 25.9, 25.4, 25.3, 24.7, 22.1, 20.6, 16.4,
12.1. IR (KBr, cmꢀ1): 3427, 2, 1709, 1638, 1591. HRMS: MþH: m/z
656.47708, calculated value for C42H62N3O3: 656.47857 (delta:
ꢀ2.27 ppm). MS–MS of m/z 656: m/z 572. Analysis calculated for
C42H61N3O3: C, 76.90; H, 9.37; N, 6.41. Found: C, 76.78; H, 9.61; N,
6.27. White solid, mp 157–159 ꢁC. Isolated yield: 43% (method E).
}
´
Sohar, P.; Hudecz, F. Tetrahedron 2001, 57, 4589–4598; (c) Mesaik, M. A.; Rahat,
S.; Khan, K. M.; Ullah, Z.; Choudhary, M. I.; Murad, S.; Ismail, Z.; Atta-ur-Rah-
man; Ahmad, A. Bioorg. Med. Chem. 2004, 12, 2049–2057; (d) Khan, K. M.;
Mughal, U. R.; Khan, M. T. H.; Ullah, Z.; Peerven, S.; Choudhary, M. I. Bioorg. Med.
Chem. 2006, 14, 6027–6033.
4. Bauer, W.; Polborn, K.; Beck, W. J. Organomet. Chem. 1999, 579, 269–279.
5. Fisk, J. S.; Mosey, R. A.; Tepe, J. J. Chem. Soc. Rev. 2007, 36, 1432–1440.
6. (a) Mu¨ller, E.; Pe´czely, G.; Skoda-Fo¨ldes, R.; Taka´cs, E.; Kokotos, G.; Bellis, E.;
4.4.11. N,N0-Dicyclohexyl-N0-(2-(5
a-androst-16-ene-17-
´
Kolla´r, L. Tetrahedron 2005, 61, 797–802; (b) Taka´cs, E.; Skoda-Fo¨ldes, R.; Acs, P.;
carboxamido)-4-methyl-thio-butanoyl)-urea (4e)
Mu¨ ller, E.; Kokotos, G.; Kolla´r, L. Lett. Org. Chem. 2006, 3, 62–67; (c) Skoda-
Fo¨ldes, R. React. Kinet. Catal. Lett. 2007, 90, 159–165.
dH (400.13 MHz, CDCl3): 7.54–7.64 (m, 1H), 6.42–6.50 (m, 1H),
6.22 (d, J 7.5 Hz, 1H), 4.78–4.86 (m, 1H), 4.09–4.19 (m, 1H), 3.62–
3.71 (m, 1H), 2.51 (t, J 6.8 Hz, 2H), 2.08 (s, 3H), 0.72–2.20 (m, 44H,
7. MS data: 2c: m/z 355 (100) (Mþ), 340 (12), 282 (14), 257 (42), 161 (35), 135 (16),
95 (22), 79 (26), 55 (19); 4c: m/z 415 (19) (Mþ), 354 (100), 285 (7), 257 (34), 161
(43), 147 (35), 121 (23), 91 (67), 67 (70), 61 (96), 55 (94).
c
8. (a) Goodman, M.; Levine, L. J. Am. Chem. Soc. 1964, 86, 2918–2922; (b) DeTar, D. F.;
Silverstein, R. J. Am. Chem. Soc. 1966, 88, 1013–1019; (c) Benoiton, N. L.; Chen, F.
M. F. J. Chem. Soc., Chem. Commun. 1981, 1225–1227; (d) Wang, Q. M.; Huang, R. Q.
J. Chem. Res., Synop. 2001, 246–247; (e) Bruckdorfer, T.; Marder, O.; Albericio, F.
Curr. Pharm. Biotechnol. 2004, 5, 29–43; (f) Iwasawa, T.; Wash, P.; Gibson, C.;
Rebek, J. Tetrahedron 2007, 63, 6506–6511; (g) Buchanan, G. W.; Rastegar, M. F.;
Enright, G. J. Fluorine Chem. 2007, 128, 1026–1028.
steroidal ring protonsþ Hex ring protonsþCH2CH2S), 0.94 (s, 3H),
0.79 (s, 3H). dC (100.62 MHz, CDCl3): 170.4,166.6,153.3,149.4,138.2,
56.8, 55.0, 54.8, 51.5, 50.3, 47.2, 46.4, 38.4, 36.4, 35.0, 33.8, 32.6, 31.9,
31.8, 31.7, 31.6, 31.5, 30.2, 29.2, 29.0, 28.8, 26.7, 25.9, 25.8, 25.4, 25.3,
24.6 (2C), 22.1, 20.6, 16.4,15.4,12.1. IR (KBr, cmꢀ1): 3452, 3329,1706,
1636, 1590. HRMS: MþH: m/z 640.44912, calculated value for
C38H62N3O3S: 640.45064 (delta: ꢀ2.38 ppm). MS–MS of m/z 640:
m/z 622 (12), 556 (100), 515 (57), 416 (14), 357 (10), 250 (12), 224
(50). Analysis calculated for C38H61N3O3S: C, 71.32; H, 9.61; N, 6.57.
Found: C, 71.61; H, 9.79; N; 6.28. White solid, mp 136–138 ꢁC.
Isolated yield: 72% (method D).
9. Huang, W. H.; Wang, M. L.; Yue, H. Synthesis 2008, 1342–1344.
10. Interestingly, the use of N,N0-diisopropylcarbodiimide instead of DCC as the
coupling agent in the reaction of amino acid derivative 3b under similar conditions
(method A) led to the exclusive formation of the N-acylurea product N,N0-diiso-
propyl-N0-(2-(5
a-androst-16-ene-17-carboxamido)-3-phenyl-propionyl)-urea. The
structure of this compound was proved by its 1H NMR spectrum: dH (400.13 MHz,
CDCl3): 7.45–7.51 (m,1H), 7.20–7.26 (m, 3H), 7.08–7.11 (m, 2H), 6.25–6.28 (m,1H), 5.
97 (d, J 6.4 Hz, 1H), 4.80–4.88 (m, 1H), 4.40–4.50 (m, 1H), 3.86–3.95 (m, 1H), 3.05
(dd, J 6.1, 13.6 Hz, 1H), 2.84 (dd, J 8.2, 13.6 Hz, 1H), 2.06–2.14 (m, 1H), 1.77–1.89
(m, 2H), 0.71–1.63 (m, 31H, steroidal ring protonsþmethyl protons of the isopropyl
groups), 0.84 (s, 3H), 0.73 (s, 3H). The presence of imide 3d or an oxazolone
derivative could not be detected in the reaction mixture.
Acknowledgements
The authors thank the Hungarian National Science Foundation
for financial support (OTKA T048391, NK71906, NI61591).
11. (a) Maruyama, H. B.; Suhara, Y.; Suzuki-Watanabe, J.; Maeshima, Y.; Shimizu, N.;
Ogura-Hamada, M.; Fujimoto, H.; Takano, K. J. Antibiot. 1975, 28, 636–647; (b)
Suhara, Y.; Maruyama, H. B.; Kotoh, Y.; Miyasaka, Y.; Yokose, K.; Shirai, H.; Takano,
K.; Quitt, P.; Lanz, P. J. Antibiot. 1975, 28, 648–655.
12. Krohn, K.; Franke, C.; Jones, P. G.; Aust, H.-J.; Draeger, S.; Shultz, B. Liebigs Ann.
Chem. 1992, 789–798.
References and notes
13. Salunke, D. B.; Hazra, B. G.; Pore, V. S. Curr. Med. Chem. 2006, 13, 813–847.
14. Dixit, M. V.; Bhat, V.; Trozzolo, A. M.; George, M. V. J. Org. Chem. 1979, 44,
4169–4173.
15. Bates, R. B.; Fletcher, F. A.; Janda, K. D.; Miller, W. A. J. Org. Chem. 1984, 49
3038.
1. (a) Ling, Y. Z.; Li, J. S.; Liu, Y.; Kato, K.; Klus, G. T.; Brodie, A. M. H. J. Med. Chem.
1997, 40, 3297–3304; (b) Njar, V. C. O.; Kato, K.; Nnane, I. P.; Grigoryev, D. N.;
Long, B. J.; Brodie, A. M. H. J. Med. Chem. 1998, 41, 902–912; (c) Jarman, M.;
Barrie, S. E.; Llera, J. M. J. Med. Chem. 1998, 41, 5375–5381; (d) Zhu, N.; Ling, Y.;
Lei, X.; Handratta, V.; Brodie, A. M. H. Steroids 2003, 68, 603–611.