A practical route for the synthesis of 17 substituted steroidal 3-thioxamides

ELSEVIER

A practical route for the synthesis of 17 substituted steroidal 34hioxamides Paride Grisenti,* Ambrogio Magni, * Ada Manzocchi,? and Patrizia Ferraboschit *Poli Industria Chimica, Quint0 Stampi, Rozzano, Milano, Italy; and fDipartimento Biochimica Medica, Universita’degli Studi di Milano, Milano, Italy

di Chimica e

A facile method for the synthesis of a series of new steroidal 3-thioxamides from the 3-0~0 compound, variously substituted at the I7 position, is described. The “one pot” reaction, using Lawesson’s reagent (4methoxyphenylthionophosphine sulphide dimer) in dichloromethane solution, gives the desired compounds with a high degree of chemoselectivity, in good yields (>80%). (Steroids 62:504-506, 1997) 0 1997 by Elsevier Science Inc.

Keywords: 3-oxo-4-azasteroids; 3-thioxo-4-azasteroids; Lawesson’s

Introduction Azasteroids are a class of compounds of wide biological interest.‘-3 3-Oxo-4-azasteroids variously substituted at the position 17 are extensively studied as competitive inhibitors of testosterone 5a-reductase.4.5 To define the structureactivity relationship of these compounds better seven 3-thioxo isosteres of known azasteroids la-gev7 were synthesized. To our knowledge only one example of a steroidal 3-thioxamide; namely, a N,N-diethyl-3-thioxo-4-methyl-4aza-5a-androstane-17@arboxamide, has been reported.7 The experimental procedure described for the synthesis of this compound consists of two steps with a 34% overall yield and requires experimental conditions incompatible with many functional groups. Lawesson’s reagent (LR) has been widely used as a powerful thionating agent for ketone, ester, and amide groups employing mild reaction condition+ and sometimes showing high regioselectivity.9 Thionation with LR, because of the mild reaction conditions, can often be carried out as the last step of a synthesis that minimizes manipulation of these unstable and unpleasant smelling compounds. The thionation reaction on different carbonyl groups is conducted under different reaction conditions; therefore, on polyfunctional molecules, it is often difficult to predict their relative reactivity.‘O

Experimental Solvents and reagents were purchased from Fluka (Buchs, Switzerland). Melting points are uncorrected. Optical rotations were measured on a Perkin-Elmer model 241 polarimeter. Unless otherwise indicated, ‘H NMR and “C NMR spectra were recorded on a Bruker AM-500 and AC-200 instrument, respectively, with Address reprint requests to Dr. Paride Grisenti, Poli Industria Chimica, Via Voltumo 42, 20089, Quint0 Stampi, Rozzano, Milano, Italy. Received September 5, 1996; accepted February 18, 1997. Steroids 62504-506, I997 0 by Elsevier Science Inc. 655 Avenue of the Americas,

New York, NY 10010

reagent; chemoselectivity;

testosterone

.5-alpha reductase

CDCl, as solvent. MS spectra were recorded on a Hewlett-Packard 5988A instrument. IR spectra were recorded in chloroform solution on a Perkin-Elmer 1600 series FTIR instrument. Analytical TLC were performed on silica gel Merck 60 F254 plates, and column chromatographies were carried out on silica gel Merck 60 (230-400 mesh).

Preparation of 3-thioazasteroids 2a-g from azasteroids la-g: General methods To a stirred solution of azasteroid (20 mmol) in dry dichloromethane (50 mL) Lawesson’s reagent was added (4.45 g, I1 mmol). The reaction mixture was stirred at room temperature for 8-10 h, then was concentrated to near %o of the initial volume and poured directly into a silica gel column (400 g). Elution with dicloromethane/methanol % afforded the desired product (80-90% yield).

17/3-hydroxy-3-thioxo-4-aza-5a-androstane 2e NaBH, (2.94 mmol, 112 mg) was added over 30 min to a solution of compound 2d (1.96 mmol, 0.60 g) in methanol (10 mL) under stirring at 0°C. Then the reaction was stirred at room temperature for 3 h. The mixture was neutralized with HCl0.1 N, the methanol was evaporated at reduced pressure, and the aqueous phase was extracted with chloroform (3 X 5 mL). The organic phase was dried on Na,SO,, filtered, and evaporated at reduced pressure to give a residue further purified by silica gel chromatography: elution with CH,ClJCH,OH 95/5afforded compound 2e (I. 17 mmol, 0.36 g, 60% yield).

Results and Discussion We found that, on a series of compounds of general formula 1, LR may be used as a selective thionating agent at position 3 employing a general experimental procedure at room temperature using dichloromethane as solvent and LR in a molar ratio of 0.55:1 with the substrate (Figure 1). Using this procedure compounds 2a-d, and 2f,g were obtained in 0039-128X/97/$17.00 PI1 SOO39- 128X(97)00003-2

Preparation

a. RI-R,-H. R,-CONHtBu

b. R,-CH,, R2-CONHtBu,R3-H

c. R,-R,-H, R,-COCH,

d. RI-H. R2-R3-0 f. R,-R,-H, R,-COOCH, e. RI-B,-II,R,-OH R3-H E. R,-CH,. R,-CONHCH(CH,CH(CH,),)CONHCH3, R3-H b. RI-CHS, R,-CONHCH(CH,CH(CH,),)CSNHCli3,

Figure 1

Synthetic scheme of obtained

products.

S-10 h with an high degree of chemoselectivity versus other functional groups at position 17. The yields for all examined compounds are over 80% after chromatographic purification. Only in the case of compound le, the reaction gives the desired product 2e with low yield (30%) together with a complex mixture of side products probably because of the interference of the hydroxy group at position 17.” However, compound 2e can be obtained in good yields (>60%) by NaBH, reduction of compound 2d. Interestingly, thionation of compound lg gives the desired compound 2g (83 %) together with a minor amount of the product of double thionation 2h (9%). (Compound 2h; elemental analysis calculated for C,,H,,N,O,S,: theoretical H = 9.22%, C = 65.94%, N = 8.54%, S = 13.04%; FoundH = 9.24%, C = 65.91%, N = 8. 51%, S = 13.03%. ‘H NMR: 0.60 (s, 18-CH,, 3H), 0.77 (s, 19-CH,, 3H), 0.86 (d, J = 6.3,

Table 1

of steroidal

3-thioxamides:

Grisenti

et al.

Leu-CH,, 3H), 0.89 (d, J = 6.3, Leu-CH,, 3H), 2.17 (t, J = 9.1, 17-CH, lH), 3.05 (d, J = 4.2, CH,-NH, 3H), 2.91 and 3.12 (dt, J = - 17.9 and 7.0,2-CH,, 2H), 3.20 (dd, J = 12.6 and 3.5, 5-CH, lH), 3.46 (s, CH,-NCS, 3H), 4.92 (m, a-CH-Leu, lH), 6.18 (d, J = 8.4, Leu-NH, lH), 9,39 (broad q, J = 4.2, NH-CH,, 1H); MS: 492(M+), 457(M-35), 414(M-78), 332(M-160), 304(M-188). MP 229-230°C; [a]o = + 11 (c = 1, CHCl,).) All the products were characterized by ‘H NMR and 13C NMR spectra analysis, as shown in Table 1. Thionated compounds present typical differences from parent oxo-compounds: a characteristic shift of the 2-CH, signal from 2.3-2.5 to 2.8-3.1 ppm at ‘H NMR analysis and a shift from 172-173 to 201-202 ppm of the C-3 signal at 13C NMR analysis. Furthermore, all obtained compounds show a decrease in polarity that is easily detected by an increase of R, values. Elemental analysis, mass spectra (MS), and IR data are in agreement with the proposed structures (Table 2). Melting point and optical rotation data for new compounds are reported in Table 3. Employing LR in dichloromethane solution at room temperature, it is possible to obtain in good yields and a high degree of chemoselectivity steroidal 3-thiolactams 2a-d and 2f, 2g. Experimental conditions are mild and compatible with other functional groups present in the molecule. Furthermore, the high degree of chemoselectivity allows introduction of the thioxo function in the last step of the reaction, avoiding the manipulation of thionated intermediates.

Acknowledgments This work was partially financially supported by Minister0 dell’Universita’ e della Ricerca Scientifica e Tecnologica (MURST).

NMR data for new compounds ‘H NMR(CDCIJa

13C NMR (CDCI,)

2a

0.66(s, 18-CH,, 3H), 0.84(s, 19-CH,, 3H), 1.32(s, t-k, 9H), 1.99(t, J = 9.1, 17-CH, lH), 2.86-2.95(m, 2-CH,, IH), 2.98-3.08(m, 5-CH and 2-CH,, 2H)

2b

0.68(s, 18-CH,, 3H), 0.81(s, 19-CH,, 3H), 1.34 (s, t-W, 9H), 2.01 (t, J = 9.1, 17-CH, IH), 2.91 and 3.11 (dt, J = -17.7 and 7.0, 2-CH,, 2H), 3.19(dd, J = 3.5 and 12.5, 5H, lH), 3.50(s, CH,-N, 3H)

2c

0.56(s, 18-CH,, 3H), 0.81(s, 19-CH,, 3H), 2.06 (s, CH,-CO, 3H), 2.47(t, J = 9.1, 17-CH, 1H). 2.79-2.90(m, 2-CH,, lH), 2.92-3.03(m, 5-CH and 2-CH,, 2H)

2d

0.85(s, 18-CH,, 3H), 0.87(s, 19-CH,, 2.44(dd, J = -19.5, 9.1, IGP-CH,, 5-CH and 2-CH,, 2H) 0.75(s, 18-CH,, 3H), 0.87(s, 19-CH,, 5-CH and 2-CH,, 2H), 3.64(t, J = 0.62(s, 18-CH,, 3H), 0.82(s, 19-CH,, 2.91 (m, 2-CH,, IH), 2.94-3.05(m,

11.83(C-19), 13.16(C-18), 28.99(t-Bu), 36.94(C-2), 57.44(C-17), 63.29(C-5), 171.55(CONH), 202.28(CS) 13.03(C-181, 14.27(C-19), 28.86(t-Bu), 37.45(CH,-N), 39.6O(C-2), 57.19 (C-17) 67.52(C-5), 171.46(CONH), 200.75(G) 11.74(C-191, 13.31(C-18), 31.35(C-21), 36.87(C-2). 63.19(&Z.), 63.35(C-17). 201.85(G), 208.18(C-20) 11.74(C-19), 13.67(C-18), 35.53(C-16), 36.8O(C-21, 63.1O(C-5). 201.64(CS), 220.2O(CO) ll.O8(C-18). 11.75(C-19), 36.85(C-2). 63.28(C-51, 81.34(C-17), 201.86(G) 11.77(C-191, 13.46(C-18), 36.98(C-2). 51.15(CH,O), 54.98(C-17), 63.26 (C-51, 174.22(COO), 201.92((X) 13.17(C-18). 14.3O(C-19). 22.21 and 22.74(Leu-CH,), 26.03(CH,-NH), 37.53(CH,-NCS). 39.65(C-2), 51.39(&H-Leu), 56.41(C-17). 67.58(C-5). 172.73 and 172.78(CONH), 200.93(G)

Product

2e 2f

29

3H), 2.06 (dt, J = -19.5, 9.1, 16~CH,, lH), lH), 2.97-2.86(m, 2-CH,, IH), 3.09-3.00(m, 3H), 2.87-2.96(m, 2-CH,, IH), 3.07-2.99(m, 9.1, 17-CH, 1H) 3H), 2.30(t, J = 9.1, 17-CH, IH), 2.825-CH and 2-CH,, 2H), 3.62(s, CH,O, 3H)

0.61(s, 18-CH,, 3H), 0.77(s, 19-CH,, 3H), 0.87(d, J = 6.3, Leu-CH,, 3H), 0.89(d, J = 6.3,Leu-CH,, 3H). 2.74(d, J = 4.9, CH,-NH, 3H), 2.91 and 3.11(dt, J = -17.0 and 7.0, 2-CH,, 2H), 3.19(dd, J = 3.5 and 12.0, 5H. lH), 3.46(s, CH,NCS, 3H), 4.44(m, &H-Leu, IH), 5.83(d, Leu-NH, J = 7.7, IH), 6.55(broad q, J = 6.32)

‘J reported are directly obtained from monodimensional

proton NMR spectra.

Steroids,

1997, vol. 62, June

505

Papers Table 2

Elemental

analysis,

MS, and IR data for new compounds

Elemental analysis for theoretical

Product

calculated found

MS

IR(cm

‘)

W-WW 2a

H = 9.81/9.83; C = 70.72l70.75; N = 7.1717.19; S = 8.21/8.19

390(M+).

375(M-15),

318(M-72)

1513,

1671

2b

C,,H&N,S H = 9.9619.97; C = 71.24i71.21; N = 6.9216.96; S = 7.92ff.90

389(M-15), 375(M-29), 404(M+), 332(M-72), 303(M-101)

1505, 1669

2c

Cz,H,,ONS H = 9.3719.35; C = 72.02i72.05; N = 4.2014.22; S = 9.6119.65

333(M+), 318(M-15). 290(M-43)

304(M-29),

1520, 1700

2d

C,,H,,ONS H = 8.9118.93; C = 70.77i70.74; N = 4.56/4.52; S = 10.50/10.53

305(M+),

290(M-15),

276(M-29)

1518, 1735

2e

C,aH,,ONS H = 9.5119.54; C = 70.31l70.35; N = 4.5614.60; S = 10.43l10.44

307(M+),

292(M-15),

277(M-30)

1080, 1519, 3605

2f

C,oH,,O,NS H = 8.9418.97; C = 68.73168.70; N = 4.0114.05; S = 9.1719.19

349(M+), 334(M-15), 290(M-59)

320(M-29),

1521, 1727

29

C,,H,AN,S H = 9.5319.57; C = 68.17/68.19 N = 8.8318.86; S = 6.7416.75

475(M+), 446(M-29), 304(M-171)

332(M-143),

1500, 1671

Table 3 Melting points (crystallization for new compounds

solvent) and optical rotation data

Product

Melting

2a 2b 2c 2d 2e

261°C (dichloromethane/methanol) 202T (acetone) 234-235°C (ethyl acetate) 259-260°C (acetonitrile) 220°C dec (dichloromethane/ methanol) 249-250°C (dichloromethanet hexane) 273-274°C (ethyl acetate)

2f 29

point (cristallization

solvent)

(c = 1 CHCI,) +64.0/+75.9 +76.7/+92.3 +112.9/+139.9 +61.0/+75.6 +24.9/+28.7

7.

+87.4/+104.2 +42.0/+51.8 8. 9.

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