PHOTOGENERATION OF AMINES FROM ALPHA-KETO CARBAMATES - DESIGN AND PREPARATION OF PHOTOACTIVE COMPOUNDS

The design and synthesis of substituted desyl (2-oxo-1,2-diphenylethyl ) groups has been investigated to create new photolabile protecting gr oups. The photoreactivity of these chromophores stems from the diverse photochemistry of the desyl group. Several chromophore designs have b een explored in which the substitution pattern of the parent desyl chr omophore was varied systematically. The required benzoin chromophores are prepared by a variety of synthetic routes, depending on the struct ure of the benzoin chromophore desired. Symmetrical benzoins are readi ly available via the benzoin condensation, Unsymmetrical benzoins incl uding 2,2-disubstituted alpha-hydroxy ketones are generally prepared v ia trimethylsilyl (TMS) masked cyanohydrins, On reaction with a Grigna rd reagent, the TMS masked cyanohydrin functions as an alpha-hydroxyca rbonyl equivalent to form alpha-hydroxy ketones, Alternatively, lithia tion of a TMS masked cyanohydrin generates a benzoyl anion equivalent which reacts with aldehydes and ketones to generate substituted benzoi ns, These desyl chromophores have significant potential as new photola bile protecting moieties for a variety of functional groups and are us ed to mask primary and secondary amines as photosensitive alpha-keto c arbamates, The substituted benzoin carbamates are readily prepared fro m the appropriate benzoin by reaction with isocyanates or by activatio n as a mixed carbonate followed by reaction with the free amine. These alpha-keto carbamates are interesting for two main reasons, First, th e facile synthesis of these materials indicates the ease of introducti on of the desyl based photolabile group. Second, these alpha-keto carb amates may be used for rapid evaluation of novel photoactive desyl bas ed chromophores.