Determination of the (2E, 4E)-Geometry of the 3,5-Dimethyl-2,4-diene System of Antibiotic 1233A by NMR Comparison with the Four Geometrical Isomers of Methyl 3,5-Dimethyl-2,4-heptadienoate

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(2E, 4E)-geometry was assigned to 1233A [(7R, 2'R, 3'R)-11-[3'-(hydroxymethyl)-4'-oxo-2'-oxetanoyl]-3,5,7-trimethyl-2,4-undecadienoic acid (1a)], an inhibitor of cholesterol biosynthesis. Both the ^1H- and ^<13>C-NMR spectra of 1a and methyl ester 1b were compared with those of the four geometrical isomers of methyl 3,5-dimethyl-2,4-heptadienoate (2). NOE experiments on 1b revealed the presence of a remarkable NOE between the proton at C-2 and those of the C-17 methyl group. Similar NOE was also observed with (2E, 4E)-2. This fact suggests the predominant existence of stable s-cis-rotamers at the single bond between C-3 and C-4 of 1b and of (2E, 4E)-2. Some MM2 calculations were attempted to show the presence of two types of stable conformers in the case of the 3,5-dimethyl-2,4-dienoate system.
社団法人日本農芸化学会の論文
1992-11-23