6533b856fe1ef96bd12b2f6d

RESEARCH PRODUCT

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 13C NMR chemical shifts

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Abstract 13 C 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 13 C NMR chemical shift calculations. Excellent linear relationships have been observed between experimental and calculated 13 C 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 P 2 1 2 1 2 1 , unit cell a=7.14710(10) A , b=11.9912(2) A , c=26.4368(5) A ). The crystalline packing of MeLC consists of continuous parallel intermolecular hydrogen bonded [3α-O H ⋯ O C24] head-to-tail polymeric chains, which are further cross-linked by many simultaneous weak C(sp 3 ) H ⋯ O -type of interactions.