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A New Approach to N-Glycosides. -ω-Carboxy-α-amino acids react with hexafluoroacetone to give exclusively five-membered lactones like (I), achieving protection of the α-amino and the adjacent carboxy group in one step. The unprotected carboxy group of the lactones can be activated by treatment with acid chlorides or TBTU. Acylation of (I) with the weak nucleophile (II) occurs with excellent regioselectivity in the presence of the base NEM. In the following step the lactone moiety reacts as an activated ester to produce N-glycosylated dipeptides on reaction with amino acid esters, cf. (III)→(V). Elongation of the peptide backbone in N-terminal position is possible without the need of a deprotection step, cf. (V)-(VII), since cleavage of the lactone ring is accompanied with the deprotection of the N-terminal amino group. Treatment of oxazolidinone (IIIa) with DMAP initiates a fragmentation reaction. -(BOETTCHER, C.; SPENGLER, J.; ESSAWY, S. A.; BURGER*, K.; Monatsh.

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Mit Hexafluoraceton als Schutzgruppenreagens und ausgehend von L‐Asparaginsäure ist die Diazocarbonylverbindung 1 erhältlich, aus der Rh‐katalysiert das bicyclische Prolinderivat 2 entsteht. Wegen dessen konkaver Form gelingt die Bildung neuer Chiralitätszentren mit hoher Stereoselektivität, und 4‐Oxo‐L‐Prolin, in 5‐Stellung substituiertes 4‐Oxo‐L‐Prolin und cis‐4‐Hydroxy‐L‐Prolin 3 sowie weitere Derivate sind sehr einfach zugänglich. R = H, CO2Et.

In only three or four steps glycosylated dipeptide and tripeptide fragments, respectively (see scheme), can be obtained from hydroxy amino acids by using a novel protecting group/activation concept. The method presented is even superior to the pentafluorophenyl ester method.