1. 3-nitro-2-pyridinesulfenyl (Npys) group. A novel selective protecting group which can be activated for peptide bond formation
R Matsueda, R Walter Int J Pept Protein Res. 1980 Nov;16(5):392-401.
The novel 3-nitro-2-pyridinesulfenyl (Npys) group, which is useful for the protection and the activation of amino and hydroxyl groups for peptide synthesis, is reported. The Npys group is readily introduced by treatment of amino acids with 3-nitro-2-pyridinesulfenyl chloride. The Npys group is easily removed by treatment with very dilute HCl, e.g. 0.1-0.2 N HCl in dioxane, but is is resistant to trifluoroacetic acid and 88% formic acid. Npys is also selectively removed under neutral conditions using triphenylphosphine or 2-pyridinethiol 1-oxide without affecting benzyloxycarbonyl (Z), tert-butyloxycarbonyl (Boc), 2-(4-biphenylyl)propyl(2)oxycarbonyl (Bpoc), 9-fluorenylmethyloxycarbonyl (Fmoc), benzyl (Bzl) or tert-butyl (tBu) protecting groups. The N-Npys and O-Npys groups when activated in the presence of RCOOH by the addition of tertiary phosphine form peptide or ester bonds via oxidation-reduction condensation. The important features of the Npys group are demonstrated through the synthesis of peptides in solution and by solid phase methodology without a formal deprotection procedure. In solid phase synthesis, 4-(Npys-oxymethyl) phenylacetic acid is used as the key intermediate for the introduction of the trifluoroacetic acid resistant 4-(oxymethyl) phenylacetamido linking group to the resin.
2. Synthesis of protected secretin 16-27 on a Merrifield resin. Examination of ammonolysis conditions for preparing carboxamide terminal protected peptides suitable for fragment condensation
D E Wright, N S Agarwal, V J Hruby Int J Pept Protein Res. 1980 Mar;15(3):271-8.
The partially protected dodecapeptide to secretin, H-Ser(Bzl)-Ala-Arg(Tos)-Leu-Gln-Arg(Tos)-Leu-Leu-Gln-Gly-Leu-Val-NH2 (protected secretin 16-27) was prepared using a standard Merrifield resin and solid phase synthesis methods. For comparative purposes the unprotected peptide also was prepared on a benz-hydrylamine resin. Contrary to previous reports, the valine C-terminal peptide can be cleaved from the resin and the amide obtained in high yield. A variety of conditions were examined to accomplish the cleavage of the peptide from the resin in its carboxamide terminal form. The best conditions found were trans-esterification followed by ammonolysis in a mixed solvent system. A thin-layer chromatography system which clearly separates the methyl ester and carboxamide terminal secretin 16-27 was developed.
3. [Synthesis, 13C-NMR and CD study of the N-terminal tridecapeptide sequence of human fibroblast interferon]
G Jung, H Brückner Hoppe Seylers Z Physiol Chem. 1981 Mar;362(3):275-89.
The N-terminal sequence H-Met-Ser-Tyr-Asn-Leu-Leu-Gly-Phe-Leu-Gln-Arg-Ser-Ser-OH (FIF[1-13]) of human fibroblast interferon HuIFN-beta(Fi) has been synthesized using the solid-phase method. After esterification of N-tert-butyloxycarbonyl-O-benzyl-L-serine cesium salt with chloromethylated polystyrene-1% divinylbenzene (loading 0.25 mmol/g) the tridecapeptide was built up stepwise. Coupling reagents and N-tert-butyloxycarbonylamino acids were used in a six-fold excess. For the second coupling 1-hydroxybenzotriazole was added during carbodiimide and 4-nitrophenyl glutaminate or asparaginate couplings. Side chain functions were masked: O-benzylserine, O-(2,6-dichlorobenzyl)tyrosine and Ng-tosylarginine. After an acetylation step the N-protection was removed by trifluoroacetic acid/dichloromethane 1:1, and for neutralisation triethylamine/-chloroform 1:9 were used, both steps with a prewash. The Ng-tosyltridecapeptide was split-off from the resin by HBr in trifluoroacetic acid and purified by repetitive precipitations. After deprotection of the guanidino group of arginine with sodium in liquid ammonia, the peptide was precipitated from acetic acid/water, chromatographed on Sephadex G-25 coarse in acetic acid/water 1:1 and precipitated from acetic acid/ether and dimethylformamide/acetone. After purification by multiplicative counter-current distribution in butanol/-5% acetic acid/propanol 5:5:1 the tridecapeptide was pure according to chromatographic, electrophoretic, enzymatic and instrumental analyses. The peptide was investigated by circular dichroism in trifluoroethanol and hexafluoroacetonesesquihydrate and 13C-nuclear magnetic resonance, which revealed an alpha-helical conformation. In order to obtain a suitable antigen the tridecapeptide was coupled to poly(L-lysine) (molecular mass 37300) via N,N'-dicyclohexylcarbodiimide followed by dialysis. The resulting poly(L-lysine)-FIF[1-13] conjugate showed a loading of 17.8 mol FIF[1-13] per mol poly(L-lysine).
