Comparison of epimeric methyl lithocholate and methyl iso-lithocholate molecules: single crystal X-ray structure of methyl lithocholate, ab initio HF/6-31G* optimized structures and experimental and calculated DFT/B3LYP C NMR chemical shifts

¹³C NMR chemical shifts have been measured and assigned for epimeric methyl 3α/β-hydroxy-5β-cholan-24-oates (methyl lithocholate 3α-OH epimer] and methyl iso-lithocholate 3β-OH epimer]). Their molecular dynamics simulations suggest that for both epimers there exists two predominant gas phase conformations, which have been further forwarded for ab initio/HF optimizations and DFT/GIAO based ¹³C NMR chemical shift calculations. Excellent linear relationships have been observed between experimental and calculated ¹³C NMR chemical shifts for both epimers. For methyl lithocholate (MeLC), the other minimum energy conformation equates very well with the single crystal X-ray structure (orthorhombic, space group P2₁2₁2₁, unit cell ). The crystalline packing of MeLC consists of continuous parallel intermolecular hydrogen bonded 3α-OH?OC24] head-to-tail polymeric chains, which are further cross-linked by many simultaneous weak C(sp³)H?O-type of interactions.