Chemoenzymatic Approach Toward the Pure Enantiomers of 2-Methyl-1,3-propanediol Mono(p-methoxybenzyl Ether).

In a route towards the enantiomerically pure 2-methylpropane-1,3-diol mono(p-methoxybenzyl ether), which is an important starting material for natural product synthesis, a kinetic resolution approach by means of lipase-catalyzed hydrolysis as well as acylation has been elaborated. Candida antarctica lipase-catalyzed hydrolysis of the corresponding racemic acetate proceeded with high enantioselectivity (E 35). During the studies, a curious phenomenon was observed, namely, that the enantioselectivity gradually declined accompanying the progress of the hydrolysis. This was due to inhibition of the enzyme-catalyzed reaction caused by the accumulation of the resultant alcohol. The rate of reaction of the more reactive enantiomer became lower. This situation prompted a new process, which would minimize the contamination of the undesired enantiomer, prior to the enzyme-catalyzed hydrolysis. This was successfully achieved with the aid of another Pseudomonas cepacia lipase-catalyzed desymmetrization, taking advantage of the prochiral nature of the starting material, 2-methyl-1,3-propanediol, and the subsequent p-methoxybenzylation under mild conditions.