NEW MATERIAL:The compound of formulaI(R is lower alkyl; X1 and X2 are H or OH-protecting group).

EXAMPLE: The compound of formula II.

USE: Synthetic intermediate of pharmaceuticals having carcinostatic activity, etc.

PROCESS: The compound of formula III (R' is lower alkyl) is hydrolyzed with esterase extracted from the tissue, organ, etc. of animals to obtain the compound of formula IV selectively. The product is, in the form of carboxylic acid or after converting to a reactive derivative such as acid chloride, made to react with a lower alkylation agent (e.g. lower alkene, lower alcoholate, etc.), and the resultant compound is treated with an alkali such as NaOH to afford the compound of formula V. The objective compound of formulaIcan be obtained by oxidizing the compound of formula V with ozone and distilling off the solvent.