Preparation of regio- and stereoisomeric di- and tetrahydrogeranylgeraniols and identification of esterifying groups in natural (bacterio)chlorophylls.

All regioisomeric di- and tetrahydrogeranylgeraniols possessing the C2C3 double bond were prepared as authentic samples. The synthetic C20-isoprenoid alcohols were separated well by gas chromatography. Based on the chromatographic analysis, the enzymatic reduction pathway of a geranylgeranyl group was investigated to identify the last stage of (bacterio)chlorophyll biosynthesis in phototrophs. The geranylgeranyl group was triply reduced to the phytyl group through the first regio- and stereospecific hydrogenation of C10C11 to C10HC11(S)H, the second of C6C7 to C6HC7(S)H, and the third of C14C15 to C14HC15H. The identification of the reduction sequence completes the biosynthetic pathways for naturally occurring chlorophyll-a and bacteriochlorophyll-a bearing a phytyl group as the esterifying moiety in the 17-propionate residues.