Enzyme preparations from Mycobacterium phlei, Escherichia coli and Galium mollugo cell suspension cultures were incubated in the presence of 4-(2'-carboxyphenyl)-4-oxobutyrate (i.e. o-succinylbenzoic acid, OSB, 1), ATP, coenzyme A and Mg2+. The main product isolated from the incubation mixture was 4-(2'-carboxyphenyl)-4-oxobutyryl coenzyme A ester (2) as determined by comparison with synthetic coenzyme A esters. Synthetic and enzymically formed 4-(2'-carboxyphenyl)-4-oxobutyryl coenzyme A ester (2) was shown to be enzymically converted to an intermediate in vitamin K2 biosynthesis viz. 1,4-dihydroxy-2-naphthoic acid (5). The enzymic formation of 2-(3'-Carboxypropionyl)benzoyl coenzyme A ester (3) and 4-(2'-carboxyphenyl)-4-oxobutyryl-di-coenzyme A ester (4) was also observed. They appeared in minor amounts, however. These esters were not convertible to 1,4-dihydroxy-2-naphthoic acid (5).