Structural characterization of polyprenols by 13C-n.m.r. spectroscopy: Signal assignments of polyprenol homologues

Abstract

The 13C-n.m.r. spectra of geraniol, nerol, four isomers of farnesol and eight isomers of geranylgeraniol were investigated as low molecular weight homologues of polyprenol. The aliphatic carbon signals were assigned by considering the correlation of chemical shifts between these compounds. The C-1 methylene carbona tom in trans units exhibited four signals around 39 ppm reflecting the cis- trans, cis- trans (α), trans- trans and trans- trans (α) linkages. The C-1 methylene carbon atom is cis units showed two signals around 32 ppm reflecting cis- cis and cis- cis linkages. Here, the θ terminal unit showed the same shielding effect as the trans unit on the subsequent unit. The geometric isomerism of the unit linked to the θ terminal unit was distinguished by the chemical shift of the C-1 methyl and C-4 methylene carbon signals. The geometric isomerism of the α terminal unit was determined from the chemical shift of the C-4 CH 2OH carbon signal. These correlations were independent of the molecular weight of polyprenol homologues.