17-Chloro-16-formyl-Δ1,3,5(10)-estratetraen-3-ol 2a (142 mg, 0.45 mmol) was added to a suspension of guanidine acetate (80 mg, 0.67 mmol) and potassium carbonate (180 mg, 1.34 mmol) in methanol (10 mL). The mixture was refluxed for 6 h until the complete conversion of the intermediates (TLC monitoring). The resulting mixture was cooled to room temperature and the solvent was removed under reduced pressure. The solid reside was washed with water (10 mL) and dried. The workup afforded the analytically pure product as colorless solid (129 mg, 89% yield). Rf 0.31 (CHCl3:MeOH, 5:0.2; visualized by UV light at 254 nm). The spectral data are consistent with those reported by Forgo and Vincze (2002); m.p. 285–287°C [m.p.lit (Forgo and Vincze, 2002) = 284–286°C]. 1H NMR (600 MHz, DMSO-d6), δ: 0.89 (s, 3H, 18-CH3), 1.32–1.36 (m, 1H, 7-CH2), 1.45–1.50 (m, 1H, 11-CH2), 1.54–1.64 (m, 2H, 8-CH2, 12-CH2), 1.65–1.68 (m, 1H, 14-CH), 1.86–1.90 (m, 1H, 7-CH2), 2.03–2.08 (m, 1H, 12-CH2), 2.20–2.25 (m, 1H, 9-CH), 2.31–2.38 (m, 2H, 11-CH2, 15-CH2), 2.62 (dd, J = 6.6, 14.4 Hz, 1H, 15-CH2), 2.69 (dt, J = 5.4, 16.2 Hz, 1H, 6-CH2), 2.77 (dt, J = 11.4, 16.2 Hz, 1H, 6-CH2), 6.36 (br.s, 2H, NH2), 6.40 (s, 1H, 4-CH), 6.45 (dd, J = 1.8, 8.4 Hz, 1H, 2-CH), 6.98 (d, 1H, J = 8.4 Hz, 1-CH), 8.00 (d, J = 1.8 Hz, 1H, 4-CH) (the signal of OH group was not observed in the 1H NMR spectrum). 13C NMR (125 MHz, DMSO-d6), δ: 17.1 (CH3), 26.0 (11-CH2), 26.6 (15-CH2), 27.1 (7-CH2), 29.1 (6-CH2), 32.9 (12-CH2), 37.4 (8-CH), 43.9 (9-CH), 45.8 (13-C), 54.4 (14-CH), 113.5 (2-CH), 115.6 (4-CH), 121.0 (16-C), 125.6 (1-CH), 128.2 (10-C), 136.7 (5-C), 152.6 (4′-CH), 157.5 (3-C), 162.9 (2′-C), 182.0 (17-C). IR (KBr), cm−1: 3361, 3181 (OH), 2930, 2858 (CH), 1637 (NH2), 1608, 1560 (C = C, C = N). HRMS (ESI) for C20H24N3O ([M+H]+): calcd 322.1914, found 322.1903.