Synthesis and cytotoxicity of 17a-aza-d-homo-androster-17-one derivatives

Article abstract of DOI:10.1016/j.bmcl.2011.04.093

A series of 17a-aza-D-homo-andrester-17-one derivatives, bearing hydroxyl, hydroximino, carbonyl and thiosemicarbazido groups at the position-3 or position-6 of steroidal nucleus, were prepared and evaluated in vitro against two human cell lines (Hela (human cervical carcinoma) and SMMC 7404 (human liver carcinoma)). The results showed that these compounds could exhibit a high cytotoxicity to Hela tumor cell line, especially for compounds 8 and 12, the IC₅₀ values are 15.1 and 14.0 nmol/mL, respectively. Our findings could provide new evidence showing the relationship between the chemical structure and biological activity and may be useful for the discovery of new anti-cancer drugs.

Full text of DOI:10.1016/j.bmcl.2011.04.093

Bioorganic & Medicinal Chemistry Letters 21 (2011) 3641–3643
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and cytotoxicity of 17a-aza-D-homo-androster-17-one derivatives
Yanmin Huang a,b, Jianguo Cui b, , Zhengguo Zhong c, Chunfang Gan b, Wenyan Zhang c, Huacan Song a,
⇑
⇑
a School of Chemistry and Chemical Engineering, SUN YAT-SEN University, Guangzhou 510275, PR China
b College of Chemistry and Life Science, Guangxi Teachers Education University, Nanning 530001, PR China
c Center for Drug Discovery, Guangxi Traditional Chinese Medical University, Nanning 530001, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of 17a-aza-
D
-homo-andrester-17-one derivatives, bearing hydroxyl, hydroximino, carbonyl and
Received 26 November 2010
Revised 2 February 2011
Accepted 21 April 2011
Available online 28 April 2011
thiosemicarbazido groups at the position-3 or position-6 of steroidal nucleus, were prepared and evalu-
ated in vitro against two human cell lines (Hela (human cervical carcinoma) and SMMC 7404 (human
liver carcinoma)). The results showed that these compounds could exhibit a high cytotoxicity to Hela
tumor cell line, especially for compounds 8 and 12, the IC50 values are 15.1 and 14.0 nmol/mL, respec-
tively. Our findings could provide new evidence showing the relationship between the chemical structure
and biological activity and may be useful for the discovery of new anti-cancer drugs.
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
17a-Aza-D-homo-andrester-17-one
derivatives
Synthesis
Cytotoxicity
Dehydroepaimdrosterone (DHEA) is endogenous steroidal
synthesized in five steps (Scheme 1). First, the compound 1 was
transformed into the corresponding 3b-acetoxy-5-androsten-17-
one (2), followed by the condensation reaction with hydroxyl-
amine hydrochloride to offer 3b-acetoxy-5-androsten-17-oxime
(3) according to the literature 10. Beckman rearrangement of
prohormone with important physiological activities, such as anti-
aging and assimilation of protein. It is also a very important inter-
mediate in the synthesis of steroid drugs. Previously, besides
applying to hormonal drugs, several modified steroid compounds,
such as aza-
D-ring, were used in the synthesis of steroids ester carrying alkyla-
tor.1–4 The result of the investigation of aza-
-homo-androsterone
D
-homo steroids that contain the NHCO group inside
compound 312 in SOCl2/THF gave 3b-acetoxy-17-aza-
androsten-17-one (4) in 78% yield. 3b-hydroxy-17-aza-
D
-homo-5-
-homo-5-
D
D
androsten-17-one (5)13 was obtained in 81% yield by deacetylation
in the aqueous solution of 13% K2CO3. Lastly, the oxidation of the
compound 5 with Jones reagent afforded the expected product,
alkylator (Fig. 1) indicated that the presence of characteristic
group, –NH–CO–, in the homo-aza steroid molecule is very impor-
tant in reducing the acute toxicity and enhance the anti-tumor
activity for the steroid compounds.5,6 However, the cytotoxicity
investigation for these kinds of compounds was mainly focused
on anti-leukemic activity. In our previous work, we found that a
steroidal compound has excellent cytotoxicity when it has the cho-
lesteric side chain and the 3- or 6-position on steroidal nucleus is
substituted by hydroxyl, hydroximino, or sodium sulphate.7–10 In
order to find novel and effective anti-tumor agents, we designed
17a-aza-
D
-homo-4-androsten-3,6,17-trione (6).14
The synthetic route and the structures of target compounds 7–
1215–18 were outlined in Scheme 2. Compound 6 was reduced by
NaBH4 in methanol into compound 7, and 6 condensed with two
equal amounts of hydroxylamine hydrochloride to afford di-oxime
compound 8 and condensed with two equal amount of thiosemi-
carbazide to generate di-thiosemicarbazido compound 9. The
17a-aza-D-homo-androstan-3,6,17-trione (10) was synthesized by
and synthesized a series of 17a-aza-
D
-homo-andrester-17-one
the reduction of 6 with NaBH4/NiCl2 and oxidation with Jones re-
agent in two steps. Using similar procedure for preparing 7 and
8, compounds 12 and 11 were obtained, respectively.
derivatives with various groups at the 3- or 6-position of the ste-
roidal nucleus. The design was based on the knowledge of our pre-
vious SARs analysis and effective enhancing of the anti-cancer
activity by transferring D-ring of 3b-hydroxy-5-androsten-17-one
into lactamide.11
Using 3b-hydroxy-5-androsten-17-one (1) as
material, 17a-aza-D-homo-4-androsten-3,6,17-trione (6) was
H3C
H
a
starting
N
O
H3C
Cl
O
N
⇑
Corresponding authors. Tel.: +86 771 3908065; fax: +86 771 3908308 (J.C.);
tel.: +86 20 84110918; fax: +86 20 84112245 (H.S.).
E-mail addresses: cuijg1954@126.com (J. Cui), yihxhc@mail.sysu.edu.cn
(H. Song).
O
Cl
Figure 1. Chemical structure of
D-homo-aza-androsterone alkylator.
0960-894X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2011.04.093

3642
Y. Huang et al. / Bioorg. Med. Chem. Lett. 21 (2011) 3641–3643
CH
O
3
CH
O
3
CH
NOH
3
CH
3
CH
3
Ac2O/Pyridine
r.t., 24 h
CH
3
NH2OH.HCl/NaAc.3H2O
95% CH CH OH, stirred,
60°C
2 h
,
3
2
HO
AcO
1
AcO
2
3
CH
SOCl2 /THF,stirred, r.t., 2 h
3H
N
O
CH
3H
N
O
CH
3H
CH
3
O
N
Jones' reagent/ acetone
CH
3
13% K2CO3 / CH3OH
stirred, reflux, 4h
CH
3
stirred, r.t., 2h
O
HO
O
AcO
6
5
4
Scheme 1. Synthesis of 17a-aza-
D-homo-4-androsten-3,6,17-trione.
CH
H
N
3
CH
H
N
3
O
O
CH
3
CH
3
HO
HON
OH
12
8
NOH
NaBH4/CH3OH
NH2OH.HCl/NaAc.3H2O
stirred, r.t., 30min
,
95% CH3CH2OH, stirred 60°C, 2 h
CH
H
N
3
O
CH
H
N
3
O
CH
3
CH
H
3
N
CH
O
3
NiCl2.6H2O/NaBH4/CH3OH
Jones' reagent/ acetone
CH
3
NaBH4/CH3OH
O
O
stirred, r.t., 30min
O
stirred, r.t., 2h
10
O
HO
6
OH
NH2OH.HCl/NaAc.3H2O
7
NH2NHCSNH2/ 95% CH3CH2OH
stirred, reflux, 2h
95% CH3CH2OH, stirred, 60°C, 2 h
CH
H
N
3
CH
H
N
3
O
O
CH
3
CH
3
HON
H
NSCHNN
2
NOH
NNHCSNH
2
11
9
Scheme 2. Syntheses of 17a-aza-D-homo-androster-17-one derivatives.
Table 1
Cytotoxicities of 17a-aza-D-homo-andrester-17-one derivatives in vitrob (IC50 in mol/La)
l
Compound
4
5
6
7
8
9
10
11
75.7
184
12
14.0
124.4
Hela
SMMC 7404
37.6
>200
65.9
>200
102.4
>200
18.8
>200
15.1
>200
28.8
80.5
53.6
60.8
a
Cytotoxicity as IC50 for each cell line is the concentration of compound which reduced by 50% the optical density of treated cells with respect to untreated cells using the
MTT assay.
b
Data represent the mean values of three independent determinations.
The cytotoxic activities of compounds 4–12 were determined
in vitro on Hela (human cervical carcinoma) and SMMC 7404 (hu-
man liver carcinoma) tumor cell lines. The MTT method was used
to analyze the antiproliferative activity. The results were summa-
in this investigation of cytotoxic activity against Hela tumor cell
line. But a contrary result was observed to the cytotoxicity against
SMMC 7404, such as the cytotoxic activity of compound 10 against
SMMC 7404 was higher than compounds 11 and 12. The introduc-
tion of hydroxyl or hydroxyimino into the 3- or 6-position of
steroid nucleus increased the cytotoxicity to Hela tumor cell line.
For example, the IC50 values of compounds 7, 8 and 12 were
rized as IC50 values in lmol/L in Table 1.
As shown in Table 1, compounds 4–12 displayed a distinct cyto-
toxicity against Hela tumor cell line, however, performed a weak
activity to almost inactivity against SMMC 7404. We previously re-
ported that the steroidal compounds bearing hydroxyl or hydroxi-
mino exhibited higher cytotoxic activities than the corresponding
compounds bearing carbonyl.9,10 The result was confirmed again
18.8, 15.1 and 14.0 lmol/L, respectively.
Interestingly, our results indicated that the presence of double
bond between positions 4 and 5 on A-ring conferred a positive
effect to the cytotoxicity against Hela tumor cell lines when both

Y. Huang et al. / Bioorg. Med. Chem. Lett. 21 (2011) 3641–3643
3643
silica gel column and eluted with ethyl acetate. The solvent was removed
under reduced pressure. The residue was purified by chromatography on silica
gel using methanol/dichloromethane (30:1) as elution to give 189 mg of 6 as a
3,6-positions of steroidal nucleus were substituted by hydroximino
(comparing compound 8 (IC50 value: 15.1) with the compound 11
(IC50 value: 75.7)). Nevertheless, when the 3,6-positions were
substituted by hydroxyl, the IC50 value was not affected regardless
of the existence of the double bond ((comparing the IC50 values of
the compound 7 (IC50 value: 18.8) and 12 (IC50 value: 14.0)).
In conclusion, we have prepared a new series of 17a-aza-
white solid. Yield: 60%. Mp 173–174 °C; IR(KBr)
1687, 1654, 1458, 1249, 1323, 1053, 935, 845, 728; 1H NMR (CDCl3, 300 MHz)
d: 1.17 (3H, s, 19-CH3), 1.24 (3H, s, 18-CH3), 2.93 (1H, dd, J = 16.5, 3.0, C7- H),
2.55–2.21 (m, 5H, C7-bH, C2-H, C16-H) 6.23 (1H, s, C4-H), 6.77 (1H, s, –NH); 13
m
/cmÀ1: 3476, 3182, 2953,
a
C
(CDCl3, 75 MHz): 200.8 (C-6), 198.9 (C-3), 171.6 (C-17), 159.2 (C-5), 125.9 (C-
4), 53.8 (C-9), 50.0 (C-13), 47.7 (C-14), 45.3 (C-7), 39.2 (C-1), 39.1 (C-10), 35.2
(C-12), 34.3 (C-16), 33.8 (C-2), 30.3 (C-8), 22.0 (C-18), 20.6 (C-15), 19.8 (C-11),
17.4 (C-19); ESI-MS m/z: 316 (M+1)+.
D
-homo-androster-17-one derivatives which were proven to be
potent anti-tumor activities against Hela tumor cell line. Com-
pounds 7, 8 and 12 were found to be more potent compounds,
therefore, the further structural modification and anti-tumor
activity study in vivo would be in progress. Our findings could
provide new evidence showing the relationship between the
chemical structure and biological activity and may be useful for
the design of novel chemotherapeutic drugs.
15. Procedure for the preparation of compound 10. To
a stirred solution of 6
(1 mmol) and NiCl2Á6H2O (1 mmol) in CH3OH (50 mL) was added NaBH4
(3 mmol) in one time at room temperature. After 30 min, the reaction was
stopped. The solution was neutralized with 1 M HCl. After evaporation of the
majority of MeOH under reduced pressure, the residue was extracted with
ethyl acetate. The combined extracts were washed with cold water and
saturated brines. After drying over anhydrous sodium sulfate, the solvent was
removed under reduced pressure. The resulting solid was dissolved in 30 mL of
acetone. The Jones’ reagent was gradually added into the solution of acetone at
0–5 °C until the orange of solution was not faded, and evaporated under
reduced pressure. The residue was subjected to chromatography (methanol/
dichloromethane = 30:1) to give 145 mg of 10 as a white solid, Yield: 46%. Mp
Acknowledgments
176–178 °C; IR(KBr) m
/cmÀ1: 3440, 3170, 2962, 2851, 1707, 1650, 1402, 1392,
1245, 1217, 1172; 1H NMR (CDCl3, 300 MHz) d: 0.96 (3H, s, 19-CH3), 1.21 (3H,
s, 18-CH3), 2.91 (1H, dd, J = 16.2, 4.2, C5-H), 6.33 (1H, s, –NH); 13C (CDCl3,
75 MHz): 210.5 (C-3), 208.0 (C-6), 171.5 (C-17), 54.2 (C-5), 53.7 (C-9), 52.1 (C-
13), 47.2 (C-14), 40.5 (C-4), 39.2 (C-7), 38.1 (C-10), 37.2 (C-1), 35.7 (C-12), 34.3
(C-16), 33.6 (C-2), 30.5 (C-8), 22.1 (C-18), 21.4 (C-15), 19.9 (C-11), 12.4 (C-19);
ESI-MS m/z: 318 (M+1)+.
The authors acknowledge the financial support of the Natural
Science Foundation of Guangxi Province (No: 2010GXNSFD
013019) and the Natural Science Foundation of Guangxi Province
(No: 2010GXNSFA013052).
16. General procedure for preparation of compounds 7 and 12. NaBH4 (4 mmol) was
added to a solution of 6 or 10 (1 mmol) in CH3OH (50 mL) in one time at room
temperature. After 30 min, the reaction was stopped. The solution was
neutralized with 1 M HCl. After evaporation of the majority of MeOH under
reduced pressure, the residue was extracted with ethyl acetate (15 mL Â 3).
The organic layer was washed with cold water and saturated brines. After
drying over anhydrous sodium sulfate, the solvent was removed under reduced
References and notes
1. Dimitrios, T. P. T.; George, D. G.; Catherine, K.; Athanasios, P.; Panaviotis, K.;
Charalambos, C. Breast Cancer Res. Treatment 2006, 97, 17.
2. Anna, I. K.; Manolis, A. F.; Evagelia, S. A.; Athanasios, P.; George, N. P.; Sotiris, S.
N. Bioorg. Med. Chem. 2008, 16, 5207.
3. Mourelatos, D.; Mylonaki, E.; Papageorgiou, A.; Boutis, L.; Paradelis, A.;
Anastasiou, A.; Catsoulacos, P. Mutat. Res. 1995, 346, 129.
4. Dimitrios, T. P. T. Cancer Lett. 2006, 243, 202.
5. Catsoulacos, P.; Catsoulacos, D. Anticancer Res. 1993, 13, 1203.
6. C. Charalambos, T.P.T. Dimitrios, Investigational New Drugs, Kluwer Acedemic
Publishers, Netherlands, 2003.
pressure and
methanol, the compound 7 or 12 was obtained as a white solid. Compound
/cmÀ1: 3411, 2937, 2855, 1638, 1446,
a crude product was obtained. After crystallization from
7, yield: 78%. Mp 201–203 °C; IR(KBr)
m
1401, 1384, 1352, 1286, 1061, 1041; 1H NMR (CDCl3, 300 MHz) d: 1.06 (3H, s,
19-CH3), 1.19 (3H, s, 18-CH3), 2.40 (1H, dd, J = 10.2, 8.1, C7-H), 2.50 (1H, dd,
J = 18.3, 6.6, C16-H), 4.21 (2H, m, C3-H, C6-H), 5.71 (1H, s, C4-H), 5.92 (1H, s, –
NH); 13C (CDCl3, 75 MHz): 171.6 (C-17), 147.9 (C-5), 120.4 (C-4), 68.2 (C-6),
67.6 (C-3), 54.3 (C-13), 53.6 (C-14), 47.1 (C-7), 40.6 (C-10), 39.9 (C-1), 37.8 (C-
12), 35.8 (C-16), 34.8 (C-2), 30.5 (C-8), 28.9 (C-18), 22.1 (C-15), 20.0 (C-11),
19.7 (C-19); ESI-MS m/z: 320 (M+1)+.
7. Cui, J.; Huang, L.; Fan, L.; Zhou, A. Steroids 2008, 73, 252.
8. Cui, J.; Fan, L.; Huang, L.; Liu, H.; Zhou, A. Steroids 2009, 74, 62.
9. Cui, J.; Wang, H.; Huang, Y.; Zhou, A. Steroids 2009, 74, 1057.
10. Cui, J.; Fan, L.; Huang, Y.; Xin, Y.; Zhou, A. Steroids 2009, 74, 989.
11. Cui, J.; Wang, H.; Huang, Y.; Zhou, A. CN: 101845075 A, 2010.09.29 [p].
12. Procedure for the preparation of compound 4. To a solution of oxime 3 (1 mmol)
in dry THF (15 mL) the solution of thionyl chloride (1.6 mL) in 4 mL dry THF
was added under argon. The solution was stirred under anhydrous conditions
for 2 h at 0 °C. Then the reaction was terminated and water was added to the
solution. The solution was neutralized with ammonia and the product was
extracted with CH2Cl2. The combined extract was washed with water and
saturated brine, dried over anhydrous Na2SO4, and evaporated under reduced
pressure to give a crude product which was chromatographed on silica gel
(elution: Vmethanol:Vdichloromethane = 1: 30) to give 270 mg of 4 as a white solid.
17. General procedure for preparation of compounds 8 and 11. Compound 6 or 10
(1 mmol) was dissolved in 40 mL 95% CH3CH2OH. After the mixture was heated
to 60 °C, CH3COONaÁ3H2O (1.2 mmol) and NH2OHÁHCl (1.3 mmol) were added
into the solution in 10 min. The mixture was stirred for 1 h at 60 °C. Then
reaction was terminated and the majority of solvent was evaporated under
reduced pressure. Distilled water was added into the reaction mixture, and the
product was extracted with ethyl acetate. The combined extract was washed
with saturated brine, dried with anhydrous sodium sulfate, and evaporated
under reduce pressure. The residue was subject to chromatography (methanol/
dichromethane (1:30)) to produce 8 or 11. Compound 8, yield: 80%. Mp 220–
Yield: 78%. Mp 167–168 °C; IR(KBr) m
/cmÀ1: 3475, 3178, 2945, 2868, 1744,
222 °C; IR(KBr)
1061, 963; 1H NMR (CD3OD, 300 MHz) d: 1.01 (3H, s, 19-CH3), 1.21 (3H, s, 18-
CH3), 2.38 (1H, dd, J = 9.0, 8.4, C7- H), 2.44 (1H, dd, J = 18.6, 6.0, C16-H), 3.09
m
/cmÀ1: 3407, 2925, 2847, 1634, 1446, 1401, 1352, 1220, 1286,
1658, 1455, 1249; 1H NMR (CDCl3, 300 MHz) d: 1.03(3H, s, 19-CH3), 1.13(3H, s,
18-CH3), 1.90 (3H, s, CH3CO–), 2.52–2.33 (3H, m, C16-H, C8-H), 4.63 (1H, m, C3-
H), 5.41 (1H, br s, C6-H), 5.88 (1H, s, –NH); 13C (CDCl3, 75 MHz) d: 171.7 (C-17),
170.5 (C@O), 139.5 (C-5), 121.1 (C-6), 73.6 (C-3), 54.2 (C-9), 49.4 (C-13), 47.9
(C-14), 37.8 (C-7), 36.8 (C-10), 36.7 (C-1), 33.3 (C-4), 32.2 (C-12), 31.2 (C-16),
30.8 (C-8), 27.6 (C-2), 22.1 (C-18), 21.4 (CH3CO), 20.9 (C-15), 20.0 (C-11), 19.2
(C-19); ESI-MS m/z: 346 (M+1)+.
a
(1H, ddd, J = 17.5, 4.8, 1.8, C2-bH), 3.59 (1H, dd, J = 15.6, 4.8, C7-bH), 6.32 (1H, s,
C4-H), 6.52 (1H, s, –NH), 6.81 (1H, s, 6-NOH), 6.88 (1H, s, 3-NOH); 13C (CD3OD,
75 MHz): 172.1 (C-17), 155.6 (C-6), 155.4 (C-3), 145.1 (C-5), 118.5 (C-4), 53.8
(C-9), 51.4 (C-13), 39.1 (C-1), 38.9 (C-10), 36.1 (C-12), 34.4 (C-16), 32.2 (C-2),
31.4 (C-8), 22.1 (C-18), 20.9 (C-15), 19.9 (C-11), 17.8 (C-19); ESI-MS m/z: 346
(M+1)+.
13. Procedure for the preparation of compound 5. K2CO3 solution (13%) of 15 mL was
added to a solution of compound 4 (1 mmol) in CH3OH (30 mL). The reaction
mixture was heated under reflux for 4 h. After completion of the reaction as
indicated by TLC, the solvent was removed under vacuum. CH2Cl2 (60 mL) was
added to dissolve a solid and the resulting solution was washed with cold
water and saturated brine. After drying over anhydrous sodium sulfate, the
solvent was removed under reduced pressure, and the resulting crude product
was purified by chromatography on silica gel using methanol/dichloromethane
(30:1) as elution to give 245 mg of 5 as a white solid. Yield: 81%. Mp 168–
18. Procedure for the preparation of compound 9.
A mixture of compound 6
(1 mmol), thiosemicarbazide (2 mmol), and a few drops of glacial acetic acid
(0.5 mL) in 95% ethanol (20 mL) was stirred at 60–70 °C for 2 h. After
completion of the reaction, the majority of solvent was evaporated and some
water was added to this solution. The mixture was extracted with CH2Cl2 and
the extract was washed with saturated brine, dried with anhydrous sodium
sulfate and evaporated under reduce pressure. The resulting residue was
chromatographed on a column of silica gel with a mixture of DCM–methanol
(20:1) to give 327 mg of compound 9 as a yellow solid. Yield: 71%. Mp 230–
170 °C; IR(KBr) m
/cmÀ1: 3452, 3162, 2933, 2904, 1670, 1625, 1433, 1401, 1045;
1H NMR (CDCl3, 600 MHz) d: 1.00 (3H, s, 19-CH3), 1.17 (3H, s, 18-CH3), 2.35–
2.31 (1H, m, C16-H), 2.40–2.33 (1H, m, C8-H), 2.48 (1H, ddd, J = 18.6, 7.2, 1.2,
231 °C; IR(KBr) m
/cmÀ1: 3452, 3338, 2941, 2859, 1638, 1580, 1462, 1350, 1221,
1150, 1071, 956; 1H NMR (DMSO-d6, 300 MHz) d: 0.92 (3H, s, 19-CH3), 1.07
(3H, s, 18-CH3), 2.86 (1H, dd, J = 18.0, 2.4, C2-bH), 3.11 (1H, dd, J = 17.0, 4.5, C7-
bH), 6.65 (1H, s, C4-H), 7.57(1H, s, –NH), 7.61 (1H, br s, –(C@S)–NH), 7.76 (1H,
br s, –(C@S)–NH), 8.25 (1H, br s, –(C@S)–NH), 8.34 (1H, br s, –(C@S)–NH), 10.32
(1H, br s, –N–NH–C), 10.67 (1H, br s, –N–NH–C); 13C (CD3OD, 75 MHz): 179.3
(–C@S), 178.9 (–C@S), 170.3 (C-17), 149.6 (C-6), 148.4 (C-3), 148.3 (C-5), 123.4
(C-4), 53.8 (C-9), 48.8 (C-13), 47.9 (C-14), 37.4 (C-1), 33.4 (C-16), 32.6 (C-2),
31.6 (C-8), 21.2 (C-18), 21.1 (C-15), 19.8 (C-11), 18.2 (C-19); ESI-MS m/z: 462
(M+1)+.
C
16-H), 3.57–3.51 (1H, m, C3-H), 5.36 (1H, t, J = 3.0, C6-H), 5.68 (1H, s, –NH); 13
C
NMR (CDCl3, 150 MHz) d: 171.6 (C-17), 140.6 (C-5), 120.8 (C-6), 71.5 (C-3), 54.2
(C-9), 49.5 (C-13), 48.1 (C-14), 41.9 (C-7), 39.9 (C-10), 36.9 (C-1), 36.7 (C-4),
32.3 (C-12), 31.5 (C-16), 31.3 (C-2), 30.8 (C-8), 22.1 (C-18), 21.0 (C-15), 20.1 (C-
11), 19.3 (C-19); ESI-MS m/z: 306 (M+1)+.
14. Procedure for the preparation of compound 6. The Jones’ reagent of 0.5 mL
(0.267 mol/L) was added dropwise to the solution of 5 (1 mmol) in 20 mL of
acetone in 10 min. The mixture was stirred at room temperature for 1 h and
then neutralized with 10% K2CO3 solution. The suspension was poured over a