PHOTOREMOVABLE PROTECTING GROUPS FOR PHOSPHORYLATION OF CHIRAL ALCOHOLS - ASYMMETRIC-SYNTHESIS OF PHOSPHOTRIESTERS OF (-)-3',5'-DIMETHOXYBENZOIN

Procedures have been developed for the preparation of dimethoxybenzoinyl (DMB) phosphate triesters that can be deprotected photochemically. These compounds can be useful in light-directed synthesis and caging. The photochemistry of a wide variety of fluorine-, oxygen-, and nitrogen-substituted benzoin acetates was examined to determine the substitution pattern in the nonacylated aromatic ring producing optimum chemical yields. Two groups, 2',3'-dimethoxybenzoin and 3',5'dimethoxybenzoin, were found to give the highest yields of the benzofuran product and were further developed for the photochemical deprotection of phosphate esters. These reactions could not be quenched, suggesting a singlet photosolvolysis mechanism. An asymmetric synthesis of 3',5'dimethoxybenzoin via the benzaldehyde cyanohydrin was developed that minimizes the number of diastereomers formed in the phosphorylation of chiral alcohols. A phosphoramidite reagent for the derivatization of alcohols was prepared and used to produce scalemic dimethoxybenzoinyl phosphate esters from pantolactone and glycerol, serine, and tyrosine derivatives. These compounds were deprotected photochemically to produce the phosphodiesters in high yield.