A novel method to (1-alkoxycarbonyloxyethylidene)-1,1-bisphosphonic acid derivatives 1a-c, where R = Et, Pr, i-Bu, from the tetramethyl ester of etidronate (3) and a novel alkoxycarbonyl chloride has been developed; products were isolated in reasonable yields (60-88%). The easy rearrangement characteristic of etidronate tetramethyl ester to tetraalkyl phosphonophosphate was advantageous.
bisphosphonate - etidronate - ester - synthesis - prodrug