Synthesis and characterization of lithocholic acid derived dipyrromethanes: precursors for pyrrole-steroidal macrocycles

Three steroidal dipyrromethanes, 3,3,24,24-tetrakis(pyrrol-2-yl)-5b-cholane 1, 3,3-bis(pyrrol-2-yl)-5b-cholan-24-oic acid 2, and methyl 3,3-bis(pyrrol-2-yl)-5b-cholan-24-oate 3, have been prepared from 3a-hydroxy-5b-cholan-24-oic acid (lithocholic acid) 4 in good overall yields. The structures of 1–3 have been fully characterized by 1H, 13C, PFG DQF 1H–1H COSY, 1H–1H ROESY, 13C DEPT-135, PFG 1H–13C HMQC, PFG 1H–13C HMBC, and PFG 1H–15N HMBC NMR spectra. Their molecular weights and compositions have been determined by ESI-TOF and EI mass spectra, and elemental analyses. The energetically optimised geometry and isotropic 13C NMR chemical shifts of 3,3,24,24-tetrakis(pyrrol-2-yl)-5b-cholane 1 have been calculated by ab initio HF/6-31G* and DFT B3PW91/6-311G* methods. q 2004 Elsevier B.V. All rights reserved.