The development of syntheses providing enantiomerically pure alpha-amino acids has intrigued generations of chemists and been the subject of intense research. This report describes a general approach to functionalized alpha-amino acids based on catalytic asymmetric synthesis. Proline catalyzed Mannich-type reactions of N-PMP-protected alpha-imino ethyl glyoxylate with a variety of unmodified ketones to provide functionalized alpha-amino acids in high yields with excellent regio-, diastereo-, and enantioselectivities. Study of seven examples yielded six with product ee values of > or = 99%. In reactions involving ketone donors where diastereoisomeric products could be formed, two adjacent stereogenic centers were created simultaneously upon carbon-carbon bond formation with complete syn-stereocontrol. Significantly, this methodology utilizes readily available and rather inexpensive starting materials, does not require any preactivation of substrates or metal ion assistance, and can be carried out on a gram scale under operationally simple reaction conditions. The keto-functionality present in the products provides a particularly attractive site for versatile modifications. This study compliments and extends our bioorganic approach to asymmetric synthesis to a versatile synthon class. Given that we have shown that a variety of optically active amino acids can be synthesized with proline catalysis, where an L-amino acid begets other L-amino acids, our results may stimulate thoughts concerning prebiotic syntheses of optically active amino acids based on this route.

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A full account of catalytic direct asymmetric Mannich-type reactions is presented describing the scope of amino acid-catalyzed additions of unmodified ketones to a large variety of imines. These reactions are performed under very mild, operationally simple, and environmentally friendly and benign conditions employing a one-pot, three-component protocol as well as preformed imines. Typically, products were obtained with high regio-and diastereoselectivities and excellent enantioselectivities. The methodology developed was applied as a powerful approach toward the synthesis of enantiomerically pure functionalized a-amino acids, g-lactones, oxime-functionalized amino acids as well as pharmacologically important targets such as (R)-cyclohexylglycine.

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