Efficient deprotection of N^G-tosylarginine with a thioanisole–trifluoromethanesulphonic acid system

Abstract

The tosyl group attached a t the guanidino function of arginine can be efficiently cleaved by a thioanisole-trifluoromethanesulphonic acid system, which can deprotect 0-2,6-dichlorobenzyltyrosine without the formation of O-to-C rearrangement products ; the NOmesitylene-2-sulphonyl group was also cleaved by a thioanisole-trifluoroacetic acid system. THE tosyl (p-tolylsulphonyl) group in No-tosylarginine, which is one of the most important protecting groups in peptide synthesis, can be removed by HF-anisole,2 but special apparatus is needed.3 Deprotection of Arg(Tos) $ by trifluoromethanesulphonic acid (TFMSA)-anisole is accomplished only under very drastic conditions such as use of a large excess of TFMSA (neat) and a high temperature.* We now report a mild and simple method for removal of the tosyl group attached at the guanidino function of arginine using a thioanisole-TFMSA system,5-* which can deprotect 0-2,6-dichlorobenzyltyrosine and O-methyltyrosine without the formation of O-to-C rearrangement products.6 paThe rate of this cleavage reaction depended on the nature of the nucleophiles used. The promoting effect on the reaction of the nucleophiles examined was in the order: thioanisole > anisole > dimethyl sulphide > phenol -0-

ON intramolecular acyl migration reaction in the development of prodrugs and the synthesis of difficult sequence‐containing bioactive peptides

“…The resulting peptide resin was cleaved with TFA-mcresol-thioanisole-H 2 O (TFA: triflouroacetic acid; 92.5:2.5:2.5:2.5) 43,44 for 90 min. An undesired peptide, Fmoc-Val-Val-Ser-Val-Val-NH 2 , was obtained at a similar rate to peptide 7, indicating that the Fmoc group of the pentapeptide-resin was not deprotected during SPPS ( Figure 8A).…”

Glycopeptide Specificity of Helper T Cells Obtained in Mouse Models for Rheumatoid Arthritis

“…In spite of its higher stability towards acids, the Cbz group can still be removed by trifluoroacetic acid (TFA) under conditions commonly used for the cleavage of peptides and glycopeptides from the solid phase. [24,33] The O-acetylated 4-and 3-deoxy-xylohexopyranosyl bromides (6) and (10) were therefore used in silver silicate promoted glycosylations of Fmoc-Hyl(Cbz)-OAll in dichloromethane, which gave 7 and 11 in 86 and 82 % yields, respectively (Scheme 1). Use of the less reactive acetobromoglucose (13) under identical conditions gave the expected bglycoside 14; however, the corresponding othoester was formed as a side-product and proved difficult to remove.…”

Amino Acid-Protecting Groups

“…It is removed with HF, TFMSA-TFA-thioanisole or Na/NH 3 . 296 It is the most used protecting group in the Boc/Bn solid phase strategy. 297 -2,2,5,7,8-Pentamethylchroman-6-sulfonyl (Pmc).…”