Esters of cyclopropanecarboxylic acid demonstrate a substantial increase in stability under both acid-and base-catalyzed hydrolytic conditions. Comparison of the stability of valacyclovir 13 with the cyclopropane analogue 14 shows that at 40° C and pH 6 the half-life of 14 is> 300 h while the value for 13 is 69.7 h. CBS-QB3 calculations on isodesmic reactions for transfer of groups from an alkane to an ester show that a cyclopropyl group ...