Ally sine

The preparation of 2 by enzymatic reductive amination provides the single enantiomer of the amino acid acetal by a shorter route than the previously published eight-step synthesis of racemic ally sine ethylene acetal. " Unlike the previously described route, the enzymatic route does not reqnire addition and removal of protecting groups, and therefore gives better atom economy. The synthesis of keto acid 1 and enzymatic reductive amination to 2 as described proved to be suitable for the preparation of the large qnantities of the vasopeptidase inhibitor needed for clinical trials. 

The milder conditions for A -amino temporary deprotection and final cleavage-deprotection from the solid support in Fmoc methodology have promoted more diversified work in the synthesis of protected phosphotyro-sine derivatives. Thus, methyl [94,102-104], benzyl [104-109], tert-butyl [104,105,109-111], dimethylamine [112], propylamine [113], isopropylamine [113], (methydiphenylsilyl)ethyl [114], and ally [104] 0,0-protected phosphotyrosine derivatives have been described. Using a test pp60 -de-rived peptide sequence in the continuous-flow method, JCitas et al. [104] reported no significant differences in the reactivities of the methyl-, benzyl-, tert-hutyl- and allyl-protected synthons or in the incorporation of subsequent residues. However, several drawbacks associated with some of the derivatives have been reported. 

Functionalized monomers. Sinee GTP is a mueh milder process than anionic polymerization, for example, numerous functionalized monomers can be polymerized. Thus trimethylsilyl and 2-(trimethylsiloxy)ethyl, allyl, 2-(ally-loxy)ethyl, and 4-vinylbenzene MA give polymers with functional groups along the chain, which were used for further modifieations (e.g., for the synthesis of graft copolymers) [232,234,251]. 

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