Novel N omega-xanthenyl-protecting groups for asparagine and glutamine, and applications to N alpha-9-fluorenylmethyloxycarbonyl (Fmoc) solid-phase peptide synthesis.
The N alpha-9-fluorenylmethyloxycarbonyl (Fmoc), N omega-9H-xanthen-9-yl (Xan), N omega-2-methoxy-9H-xanthen-9-yl (2-Moxan) or N omega-3-methoxy-9H-xanthen-9-yl (3-Moxan) derivatives of asparagine and glutamine were prepared conveniently by acid-catalyzed reactions of appropriate xanthydrols with Fmoc-Asn-OH and Fmoc-Gln-OH. The Xan and 2-Moxan protected derivatives have been used in Fmoc solid-phase syntheses of several challenging peptides: a modified Riniker's peptide to probe tryptophanalkylation side reactions, Briand's peptide to assess deblocking, at the N-terminus and Marshall's ACP (65-74) to test difficult couplings. Removal of the Asn and Gln side-chain protection occurred concomitantly with release of peptide from the support, under the conditions for acidolytic cleavage of the tris(alkoxy)benzylamide (PAL) anchoring linkage by use of trifluoroacetic acid/scavenger mixtures. For each of the model peptides, the products obtained by the new protection schemes were purer than those obtained with N omega-2,4,6-trimethoxybenzyl (Tmob) or N omega-triphenylmethyl (Trt) protection for Asn and Gln.
Han
Y
Y
University of Minnesota, Minneapolis, USA.
Solé
N A
NA
Tejbrant
J
J
Barany
G
G
D000596:Amino Acids / Q000737:chemistry*; D001216:Asparagine / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D005449:Fluorenes / Q000737:chemistry*; D005973:Glutamine / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D010455:Peptides / Q000138:chemical synthesis*; D014966:Xanthenes / Q000737:chemistry*
D000596:Amino Acids; D005449:Fluorenes; C016456:N(alpha)-fluorenylmethyloxycarbonylamino acids; D010455:Peptides; D014966:Xanthenes; D005973:Glutamine; D001216:Asparagine