Diastereomeric tripeptides

More recently, Baldwin etal. (136) prepared samples of stereospecifically deuterated DL-cysteine by the method outlined in Scheme 43, and converted these to diastereomeric tripeptides that could be separated. It is of interest that the azide substitution 139- 140 occurs with retention of configuration in this synthesis. 

D.L Boger et al. reported the total synthesis of bleomycin A2. They devised an efficient synthesis for the construction of the tripeptide S, tetrapeptide S, and pentapeptide S subunits of the natural product." " " In their strategy, they utilized an Evans aidoi reaction between the (Z)-enolate derived from (S)-4-isopropyl-3-propionyl-oxazolidin-2-one and A/-Boc-D-alaninal. In order to synthesize one of the diastereomers of the pentapeptide S subunit, they carried out an Evans aidoi reaction between the same aldehyde and the (Z)-enolate of (R)-4-isopropyl-3-propionyl-oxazolidin-2-one. The formation of the diastereomeric syn aldol product in this reaction clearly shows that the stereochemical outcome of the transformation is determined by the chiral auxiliary. 

For the synthesis of bis-3-lactam (JJ) (Scheme 14), the synthetic equivalent of a tripeptide, a quite effective asymmetric reaction in the formation of 3-lactam was found The azidoketene cycloaddition to a diastereomerically pure 3-benzylideneamino-3-lactam or proceeds in a completely stereoselective manner... 

Meiji Seika obtains the tripeptide (Bialaphos) by fermentation and sells it under the trade name Herbiace . Hoechst developed a chemical synthesis for glufosinate (the diastereomeric mixture of phosphinothricin). The methylphos-phonite monoester serves as the key building, and is readily accessible by two routes ... 

The successful separation of dipeptide diastereomers has been reported by Wieland and Bende (14), Taschner et al. (15), and Pravada et al. (16) either as the free peptides or as the N-protected methyl esters. Hubert and Dellacherie (5) separated diastereomeric p-nitrophenyl (Np) esters of N-protected di- and tripeptides starting from pure L-methionine and DL-alanine, they synthesized Np-S-L-Met-DL-Ala-O-Np and Np-S-L-Met-L-Met-DL-Ala-O-Np. The separation was achieved on silica gel F254 precoated (Merck) plates. TLC separation of diastereomeric dipeptides has been well documented by Arendt et al. (17) and Lepri et al. (18). 

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