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Stereoselective Synthesis and NMR Characterization of C‐24 Epimeric Pairs of 24‐Alkyl Oxysterols
Author(s) -
Ogawa Shoujiro,
Kawamoto Hiroaki,
Mitsuma Takashi,
Fujimori Hiroki,
Higashi Tatsuya,
Iida Takashi
Publication year - 2013
Publication title -
lipids
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.601
H-Index - 120
eISSN - 1558-9307
pISSN - 0024-4201
DOI - 10.1007/s11745-012-3739-1
Subject(s) - chemistry , alkyl , stereochemistry , side chain , oxysterol , stereoselectivity , cholestane , octane , two dimensional nuclear magnetic resonance spectroscopy , catalysis , organic chemistry , biochemistry , cholesterol , polymer
Two pairs of C‐24 epimeric (24 R )‐/(24 S )‐24‐hydroxy‐24‐methyl‐5 α ‐cholestan‐3 β ‐yl acetates and (24 R )‐/(24 S )‐25‐hydroxy‐24‐methyl‐5 α ‐cholestan‐3 β ‐yl acetates as well as some related 24‐ethyl oxysterol analogs were stereoselectively synthesized directly from the respective parent 24‐alkyl sterols by a remote O ‐insertion reaction with 2,6‐dichloropyridine N ‐oxide (DCP) in the presence of a catalytic amount of (5,10,15,20‐tetramesitylporphrinate) ruthenium(II) carbonyl complex [Ru(TMP)CO] and HBr. 1 H‐ and 13 C‐NMR signals serving to differentiate each of the two epimeric pairs were interpreted. The C‐24 alkyl oxysterols epimeric at C‐24 were found to be effectively characterized by the aromatic solvent‐induced shift (ASIS) by C 5 D 5 N, particularly for the difference in the 13 C resonances in the substituted cholestane side chain. A method for differentiating the 1 H and 13 C signal assignment of the terminal 26‐/27‐CH 3 in the iso ‐octane side chain was also discussed on the basis of a combined use of the preferred conformational analysis and HMQC and HMBC techniques. The present method may be useful for determining the stereochemical configuration at C‐24 of this type of 24‐alkyl oxysterols.