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Asymmetric catalytic N-phosphonyl imine chemistry: the use of primary free amino acids and Et2AlCN for asymmetric catalytic Strecker reaction.

ABSTRACT: The new asymmetric catalytic Strecker reaction of achiral N-phosphonyl imines has been established. Excellent enantioselectivity (95.2-99.7% ee) and yields (89-97%) have been achieved by using primary free natural amino acids as catalysts and Et(2)AlCN as nucleophile. This work also presents the novel use of nonvolatile and inexpensive Et(2)AlCN in asymmetric catalysis. The N-phosphonyl protecting group enabled simple product purification to be achieved simply by washing the crude products with hexane, which is defined as the GAP chemistry (GAP: Group-Assistant-Purification). It can also be readily cleaved and recycled under mild condition to give a quantitative recovery of N,N'-bis(naphthalen-1-ylmethyl)ethane-1,2-diamine. A new mechanism was proposed for this reaction and was supported by experimental observations.

SUBMITTER: Kaur P

PROVIDER: S-EPMC2912979 | biostudies-literature | 2010 Aug

REPOSITORIES: biostudies-literature

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Asymmetric catalytic N-phosphonyl imine chemistry: the use of primary free amino acids and Et2AlCN for asymmetric catalytic Strecker reaction.

Kaur Parminder P Pindi Suresh S Wever Walter W Rajale Trideep T Li Guigen G

The Journal of organic chemistry 20100801 15

The new asymmetric catalytic Strecker reaction of achiral N-phosphonyl imines has been established. Excellent enantioselectivity (95.2-99.7% ee) and yields (89-97%) have been achieved by using primary free natural amino acids as catalysts and Et(2)AlCN as nucleophile. This work also presents the novel use of nonvolatile and inexpensive Et(2)AlCN in asymmetric catalysis. The N-phosphonyl protecting group enabled simple product purification to be achieved simply by washing the crude products with ...[more]

PMID: 20597482

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Project description:Alpha-amino acids are the building blocks of proteins and are widely used as components of medicinally active molecules and chiral catalysts. Efficient chemo-enzymatic methods for the synthesis of enantioenriched alpha-amino acids have been developed, but it is still a challenge to obtain non-natural amino acids. Alkene hydrogenation is broadly useful for the enantioselective catalytic synthesis of many classes of amino acids, but it is not possible to obtain alpha-amino acids bearing aryl or quaternary alkyl alpha-substituents using this method. The Strecker synthesis-the reaction of an imine or imine equivalent with hydrogen cyanide, followed by nitrile hydrolysis-is an especially versatile chemical method for the synthesis of racemic alpha-amino acids. Asymmetric Strecker syntheses using stoichiometric amounts of a chiral reagent have been applied successfully on gram-to-kilogram scales, yielding enantiomerically enriched alpha-amino acids. In principle, Strecker syntheses employing sub-stoichiometric quantities of a chiral reagent could provide a practical alternative to these approaches, but the reported catalytic asymmetric methods have seen limited use on preparative scales (more than a gram). The limited utility of existing catalytic methods may be due to several important factors, including the relatively complex and precious nature of the catalysts and the requisite use of hazardous cyanide sources. Here we report a new catalytic asymmetric method for the syntheses of highly enantiomerically enriched non-natural amino acids using a simple chiral amido-thiourea catalyst to control the key hydrocyanation step. This catalyst is robust, without sensitive functional groups, so it is compatible with aqueous cyanide salts, which are safer and easier to handle than other cyanide sources; this makes the method adaptable to large-scale synthesis. We have used this new method to obtain enantiopure amino acids that are not readily prepared by enzymatic methods or by chemical hydrogenation.

Dataset Information

Asymmetric catalytic N-phosphonyl imine chemistry: the use of primary free amino acids and Et2AlCN for asymmetric catalytic Strecker reaction.

Publications

Asymmetric catalytic N-phosphonyl imine chemistry: the use of primary free amino acids and Et2AlCN for asymmetric catalytic Strecker reaction.

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