A process is disclosed for the preparation of a compound having the general formula: ##STR1## wherein n is an integer of from 2 to 4, R.sub.1 is an ester-forming moiety effective as a protecting group for a carboxyl group, and R.sub.2 is hydroxymethyl, formyl or carboxyl. The compounds (I) are useful as intermediates for the preparation of polyprenyl compounds having hypotensive and anti-ulcer activity. The process of the invention includes cultivating a microorganism selected from a strain of the genus Nocardia called BPM 1613, FERM-P No. 1609, Corynebacterium equi IAM 1038, Candida lipolytica IFO 0746, and Mycobacterium smegmatis IFO 3083, in a nutritive culture medium, in the presence of a compound having the general formula: ##STR2## wherein R.sub.3 is an ester-forming moiety effective as a protecting group for a carboxyl group, whereby the microorganism utilizes the compound (II) as a carbon source and oxidizes the compound (II), thereby converting the compound (II) into the compound (I).