The nitroacetyl (S)-proline esters (1,3,5) are reduced by zinc-NH4Cl to the hydroxylamine stage and cyclized to provide the novel chiral bicyclic hydroxamic acids (2,4,6). Michael addition of allyl acrylate on nitroacetic acid derivatives followed by Pd(0) catalyzed intramolecular allyl transfer and subsequent reduction of the nitro group yielded a novel class of cyclic hydroxamic acids related to pyroglutamic acid.
Nitroacetyl Group as a Peptide Synthon: Synthesis of Dipeptides with an α,α-Bisallylglycine Residue at the N-Terminus
N-Nitroacetyl derivatives of L-proline, L-valine, and L-phenylalanine esters were prepared in two steps under mild conditions (Scheme 2).Regiospecific mono- and bis-allylation of these nitroacetyl derivatives were accomplished in presence of a Pd(0) catalyst.The bis-allyl derivatives 7-9 were obtained in 40-75 percent yield.The tertiary NO2 group in these compounds could be transformed into an acetylamino group by Zn/AcOH/Ac2O.The final products 11-13 are dipeptides in which the N-terminal glycine residue bears two α-allyl substituents.
The potential of the nitroacetyl group in peptide synthesis has been demonstrated by converting N-nitroacetylproline ethyl ester into cyclo(L-Leu-L-Pro).
Manjunatha, Sulur G.,Rajappa, Srinivasachari
p. 372 - 373
(2007/10/02)
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