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Synthesis of Polypeptide by Phosphorylation of A-Amino Acid Salts

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Synthesis of Polypeptide by Phosphorylation of A-Amino Acid Salts Polymer Journal, Vol. 8, No. 1, pp 129-130 (1976) SHORT COMMUNICATION Synthesis of Polypeptide by Phosphorylation of a-Amino Acid Salts Naoya OGATA, Hozumi TANAKA, and Kazutoyo UNo Department of Chemistry, Sophia University, 7 Kioi-cho, Chiyoda-ku, Tokyo 102, Japan. (Received June 23, 1975) KEY WORDS Polypeptide I a-Amino Acid I Polycondensation Phosphorylation I Triaryl Phosphite I Imidazole I As is well known, there are many routes to the solvents. After a given period, the gel solution synthesis of polypeptides which have been deve­ was poured into excess acetone and the precipi­ loped by a stepwise polymerization of a-amino tated polymer was filtered, followed by washing acid derivatives, including N-carboxyanhydride with water and drying. Solution viscosities of or active esters of a-amino acids. Direct poly­ the polymers were measured in dichloroacetic condensation of a-amino acids has been reported acid (0.5 gjdl) at 30°C. by Yamazaki/ in which several a-amino acids Table I presents the results of the polycon­ were subjected to polycondensation to yield poly­ densation of various salts of glycine in dimethyl­ peptides by usiug triaryl phosphite and pyridine acetamide (DMAc) solution. Identification of as initiators. On the other hand, we have re­ the polymers from their glycine salts was carried ported in previous papers2 - 4 that nylon salts out by infrared and elemental analyses, which from dicarboxylic acids and diamines were easily also supported the existence of the polyglycine subjected to a polycondensation reaction to pro­ structure. The sulfuric acid salt of glycine duce polyamide in the presence of triaryl phos­ transformed into polyglycine in almost quanti­ phite and imidazole under mild conditions. tative yield, although the solution viscosity of However, when the phosphorylation reaction the resulting polyglycine was not so high. using triaryl phosphite and imidazole was applied Table II summarizes the results of the poly­ to the polycondensation of a-amino acids, only condensation of the hydrochloric acid salt of a dimerization reaction of the two amino acids glycine in various solvents at room temperature. having protective groups could occur; no poly­ It is seen that amide solvents such as dimethyl­ peptide was obtained by the direct polyconden­ formamide (DMF) or DMAc were favorable for sation of a-amino acids.2 ' 5 Recently, it was Table I. Polycondensation of glycine salts found that polypeptide was obtained in a good by phosphorylation in DMAc yield by the phosphorylation reaction, when an at room temperature• acid salt of a-amino acids was used instead of free a-amino acids. This paper deals with the Polymer synthesis of polypeptide from a-amino acids salts Glycine salt Time, hr Yield, % l'}inh by the phosphorylation with triaryl phosphite and imidazole under mild conditions. H2S04 50 93 0.15 a-Amino acid salts prepared from a-amino HCl 24 48 0.08 acids and mineral acids were suspended in various CHaCOOH 48 43 0.09 solvents with a vigorous stirring in the presence CHaCsH4SOaH 24 43 0.08 AlCla 48 14 of given amounts of triaryl phosphite and imi­ dazole. The suspension of a-amino acid salts • Monomer concn, 0.5 moll!; imidazole, I moll!; gradually transformed into a gel swollen by triphenyl phosphite, 0.5 moll!. 129 N. OGATA, H. TANAKA, and K. UNo Table II. Polycondensation of glycine Table III. Polycondensation of various a-amino hydrochloride in various solvents acid salts in DMAc at room temperature at room temperature• HCl salt• H2SO, salt" Polymer a-Amino acid Polymer, Polymer, Time, 1Jinh Solvent hr Yield, % 96 % 1]inh Glycine 48 0.08 74 0.15 Dimethylformamide 24 49 0.08 Alanine 11 0.09 Dimethylacetamide 24 48 0.08 Valine 0 88 0.13 N-Methyl-a-pyrrolidone 24 44 0.08 Leucine 0 60 0.11 Pyridine 24 13 Phenyl alanine 24 76 0.07 Tetrahydrofuran 24 10 Glycylglycine 31 71 0.10 Dioxane 25 4 Nitrobenzene 25 Trace • Monomer concn, 0.5 moljl; imidazole, 1 molj/; Dimethylsulfoxide 25 0 triphenyl phosphite, 0.5 mo!jl; time, 24 hr. Hexamethylphosphotriamide 24 0 b Monomer concn, 0.5 mo!jl; imidazole, 1.5 mo!jl; m-Cresol 24 0 triphenyl phosphite, 0.5 moljl; time, 47 hr. Benzene 24 0 Ethanol 24 0 viscosities. Acetonitrile 24 0 Table III indicates the results of the poly­ condensation of various acid salts of a-amino • Monomer concn, 0.5 moljl; imidazole, 1 molj/; triphenyl phosphite, 0.5 moljl. acids by the phosphorylation reaction. It is seen in Table III that the yields of polypeptide 100 depended on the kind of salt; generally speaking, 0 sulfuric acid salts are seen to be superior to 80 I hydrochloric acid salts with respect to polymer 0 '- 0 Q) yields. This dependence on the salt type might E >. 60 be related to the dissociation of the ammonium 0 0... group of the a-amino acid salt. 0 40 The reaction mechanism of the a-amino acid u •,-; • c;; •- 0 salts by the phosphorylation reaction will be 0 >- 0 o-- discussed in a later paper. A tentative expla­ 0 nation is that the amino group is protected by 50 100 the salt formation and an exclusive phosphory­ Ti me(hr) lation of the carboxyl group of the a-amino acid Figure 1. Polycondensation of glycine salts by might occur, resulting in an easier formation phosphorylation: (e) HCl salt; (0) H2S04 salt; of polypeptide. monomer concn, 0.5 moljl; imidazole, 1 molj/; tri­ phenyl phosphite, 0.5 moljl; room temperature. REFERENCES polymer yields. Figure 1 indicates the polycon­ 1. N. Yamazaki, F. Higashi, and J. Kawabata, J. densation behaviors of the sulfuric or hydro­ Polym. Sci., Polym. Chem. Ed., 12, 2149 (1974). chloric acids salts of glycine in DMAc solution 2. N. Ogata and H. Tanaka, Polymer J., 2 672 in terms of the polymer yields. The polymer (1971). yields reached maximum after a certain period. 3. N. Ogata and H. Tanaka, ibid., 3, 365 (1973). Temperatures higher than 60°C also caused a 4. N. Ogata and H. Tanaka, ibid., 6, 461 (1974). decrease in polymer yields and in solution 5. Yu. V. Mitin, eta!., Tetrahedron Lett., 5267 (1969). 130 Polymer J., Vol. 8, No. 1, 1976 .
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