Acylamino group, activating effects

Rhodium-BisP and -MiniPHOS catalysts are capable of high enantioselective reductions of dehydroamino acids in 96-99.9% ee.109 A variety of aryl enamides give optically active amides with 96-99% ee with the exception of ort/jo-substituted substrates.111 Despite the high enantio-selectivity, the rate of reaction in this transformation is slow. Rhodium-BisP and -MiniPHOS catalysts perform excellently in the asymmetric reduction of ( >P-(acylamino)acrylates to the corresponding protected-P-amino esters in 95-99% ee.112 Within the family of BisP and MiniPHOS, the ligands that contain t-Bu groups were found to be the most effective in a variety of asymmetric hydrogenations. 

The use of organotransition metal chemistry to effect the synthesis of complex molecules under exceptionally mild conditions has been applied to the synthesis of the sensitive p-lactam nucleus by a number of research groups. Through the use of this methodology the synthesis of the typical C-3-acylamino-substituted compounds as well as novel structures with unexpected antibacterial activity has been achieved. 

Activation of the carboxyl group in itself is conducive to racemization. The otherwise chirally stable acylamino acids and peptides can lose chiral homogeneity once their free carboxyl group is converted into a reactive derivative. The electron-withdrawing effect of the activating group (X) renders the proton on the a-carbon atom slightly acidic and hence abstractable by base and chirality is, of course, lost in the carbanion. This simple mechanism, however, is operative only... 

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