Peptide Chain at the Carboxyl Function of MDP

The synthesis of the N-acetyl-muramyl tetrapeptide (61) (33,44), which has the peptide sequence of the monomeric glycopeptide unit of many peptidoglycans, and that of its diastereoisomer (62) (45) has been reported. The fully protected tetrapeptide was prepared by coupling the two fragments BOC-L-Ala-D-isoGln and Lys(Z)-D-(or L)-Ala-OBzl by means of the mixed anhydride method. 

Three N-acetyl-muramyl-tripeptides were synthesized which bear on the carboxyl function of MDP either a L-lysyl, (63) (55, 44) a L-alanyl, (64), or a D-alanyl, (65) (45) residue. All of these compounds were obtained by the general stepwise method of synthesis. The hydrogenolysis step leading to (61 and 63) was complete only in presence of 0.5 equivalents of hydrochloric acid (52). 

The glycopeptide (66), substituted on both the a and y-carboxyl function of the D-glutamic residue by an amino-acyl and a dipeptidyl residue, was prepared via the key intermediate BOC-D-Glu-Gly-OBzl. The latter was synthesized as its dicyclohexylamine salt by treatment of 

The glycopeptide (67) which is a fragment of the peptidoglycan of P. peterssonii and S. ventriculi, contains the less frequently occuring L-L-isomer. It was synthesized (5) by condensation of the fragments and subsequent one-step hydrogenolysis. Thus, by means of N-ethoxy- 

N-acetyl-muramyl-tetrapeptides which contain the more frequently occurring a,E-w yo-diaminopimelyl residue have apparently not been prepared except by biosynthesis, in spite of the synthesis of non-symetric a,e-wejo-diaminopimelyl-tetrapeptides which represents a striking success after a year-long effort (7). 

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