Yongxin Han, G. Barany
Jun 13, 1997
Citations
0
Influential Citations
37
Citations
Journal
Journal of Organic Chemistry
Abstract
The 9H-xanthen-9-yl (Xan) and 2-methoxy-9H-xanthen-9-yl (2-Moxan) groups can be introduced onto sulfhydryl functions by S-alkylation reactions involving the corresponding xanthydrols, plus trifluoroacetic acid (TFA) as catalyst. Conversely, these groups are removed rapidly by acid in the presence of appropriate silane or thiol scavengers. The 3-methoxy-9H-xanthen-9-yl (3-Moxan) derivative was also studied, but abandoned for several reasons including challenging synthesis, excessive lability to acid, and insufficient stability in the presence of base. The Nα-9-fluorenylmethyloxycarbonyl (Fmoc), S-Xan or 2-Moxan-protected cysteine derivatives were prepared and applied to the solid-phase syntheses of several model peptides. Selective removal of S-Xan and S-2-Moxan groups, while retaining tris(alkoxybenzyl)amide (PAL) anchoring, is best accomplished with TFA−CH2Cl2−Et3SiH (1:98.5:0.5), 25 °C, 2 h. Alternatively, oxidative deprotection of S-Xan or S-2-Moxan with iodine (10−20 equiv) or thallium(III) tris(trifl...