126. Amino-acids and peptides. Part XXI. Removal of the nitro-group from nitroarginine and peptides of nitroarginine by electrolytic reduction

Abstract

Nitro-L-arginine can be reduced at a mercury cathode to L-arginine nearly quantitatively, and this new method for the removal of the nitro-group has been used in the synthesis of L-arginyl-L-leucine, -L-valine, -glycine, -L-proline, -S-benzyl-L-cysteine, and -S-benzylthiomethyl-L-cysteine, and of L-prolyl-L-arginine. The procedure succeeds with sulphur-containing peptides, for which catalytic hydrogenation fails. By the use of a mixture of tetrahydrofuran and N-sulphuric acid as solvent during the reduction, Na-benzyloxycarbonyl-Nu-nitro-L-arginylglycine was converted into NQ-benzyloxycarbonyl-L-arginylglycine.

Amino-acids and peptides. Part 42. Synthesis of a protected docosa peptide having the sequence of mast-cell degranulating peptide

“…to monitor the progress of the syntheses. Both the protected hexapeptide ester (2a) and especially its acid (2b) (see below) Optical rotations were measured in chloroform [compounds (6) and (7)] or dimethylformamide [compounds ( 8 ) , (9), and (2a)], c 1.0. The product was extracted into 0.7~-citric acid from solution in ethyl acetateether and was then extracted from the basified aqueous layer into ethyl acetate.…”

Amino-acids and peptides. Part 45. The protection of the thiol function of cysteine and the imidazole-N of histidine by the diphenyl-4-pyridylmethyl group

“…Coupling was by means of dicyclohexylcarbodi-jmidc and l-hydroxybenzotriazd~ in tetrahyd rofurari for compounds (14) and (16), in dichloromethane for compound (15), and in diinethylformamide for compound5 ( I i) arid (8) Optical rotations were measured in dimethylformamide (c 1 .O).…”

“…N-t-Butoxycarbonyl-S-(diphenyl-4-pyridylmethyl) -Lcysteinyl-L-alanine.-Hydrolysis of compound ( 14) (see Table 1) by lhl-sodium hydroxide (1.2 equiv.) in dioxan at room temperature for 30 min gave the acid (yield, 96Yo), m.p.…”