Use of the p-nitrocinnamyloxycarbonyl (Noc) radical as amino-protective group

摘要

The use of the p-nitrocinnamyloxycarbonyl (Noc) radical as amino-protective group, in particular for peptide and glycopeptide syntheses, is described. The p-nitrocinnamyloxycarbonyl (Noc) radical represents a valuable protective group which can be eliminated under neutral conditions. It has a higher acid stability than the unsubstituted allyloxycarbonyl group and has a strong UV absorption ( lambda max = 310 nm) which simplifies analytical monitoring even for solid-phase syntheses using the Noc protective group; in addition, almost all Noc-protected amino acids are crystalline. The Noc group is eliminated under virtually neutral conditions by palladium(0)-catalysed allyl transfer, using as a particularly effective allyl acceptor N,N'-dimethylbarbituric acid. In comparison with the rhodium(I)-catalysed elimination of unsubstituted allyl protective groups, the Noc group is stable so that it represents an important extension of the potential protective groups for synthesising peptides and glycopeptides.