Add time:09/25/2019         Source:infona.pl

The unnatural amino acid analogue, 4-(phosphonomethyl)phenylalanine (Pmp, 2), has proven to be a valuable tool for studying protein-tyrosine kinase dependent signal transduction, where it is most often incorporated into peptides or peptide mimetics as a phosphatase-stable phosphotyrosyl mimetic. Although Pmp has been prepared previously bearing a number of protection strategies, the N ^α -Fmoc 4-[di-(tert-butyl)phosphonomethyl] phenylalanine form [(N ^α -Fmoc-l-Pmp( ^t Bu ₂ )-OH, 3] is particularly attractive since it can be cleanly introduced into peptides using standard Fmoc protocols. Synthesis of 3 was first reported as its (d/l)-racemate, and subsequently as its l-3 enantiomer, with the latter synthesis having relied on induction of chirality using a camphor sultam auxillary. Reported herein is an alternate enantioselective synthesis of l-3 in high enantiomeric purity by procedures which derive the stereochemistry of the final product directly from the starting amino acid, without the need for chiral induction. A key feature of the route is the racemization-free nucleophilic substitution of lithium di-tert-butyl phosphite onto protected 4-bromomethylphenylalanine (17).

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