Various kinds of sequential polypeptides were prepared by direct polymerization of peptides in the presence of diphenylphosphoryl azide (DPPA). Typically, polymerization reactions were carried out as follows; monomer peptide concentration: 300 mg/0,6 mL of DMSO (or some other solvent); amount of DPPA: 1,3 mol/mol peptide; amount of triethylamine: 2,3 mol/mol peptide (+1,0 mol/mol peptide in case of peptide hydrochloride); reaction time: 2 days at room temperature. Molecular weights of the resulting sequential polypeptides were estimated from their intrinsic viscosities in dichloroacetic acid and SDS-polyacrylamide gel electrophoresis; they range from 4000 to 30000. The purity of the sequential polypeptides was confirmed by IR, elemental analysis and optical rotation measurements of their acid total hydrolysates.

Polypeptides can be prepared by stirring an amino acid solution in the presence of diphenylphosphoryl azide (DPPA) and an adequate tertiary amine. Generally, 1,3 mol of DPPA and 2,3 mol of triethylamine per mol of amino acid gave the best result. Polymerization of various amino acids (Gly, Ala, Leu, Phe, Met, Glu(OBzl), Glu(OMe), Cys(Bzl), Ser(Bzl), His(Bzl), Lys(Z), Arg(Tos), Arg(N02), Arg(Mts), etc.; cf. Tab. 2) in dimethyl sulfoxide, N,N-dimethylformamide, 1,4-dioxane, pyridine, etc. gave the corresponding polypeptides with molecular weights as estimated from their intrinsic viscosities between 3 000 and 16000, in reasonable yields. The purity of the resulting polypeptides was confirmed by IR, elemental analysis and optical rotation measurements of their acid total hydrolysates.

No abstract

ABSTRACT:The polymerization reactions of L-alanylglycine with diphenylphosphoryl azide (DPPA) were investigated under various reaction conditions. Dimethyl sulfoxide and triethylamine were found to be the most suitable solvent and base, respectively, for this polymerization reaction. A reaction time of two days at room temperature, employing 1.3 equivalent moles of DPPA and 2.6 equivalent moles of triethylamine corresponding to the amount of L-alanylglycine were considered to be the most appropriate reaction condition. In this case, poly(L-alanylglycine) which has the intrinsic viscosity of 0.16 in dichloroacetic acid at 25°C was obtained in 43% yield. Its infrared absorption spectrum and elemental analysis, and the amino acid analysis or the optical rotation for the acid hydrolysate indicated the high purity of poly(L-alanylglycine) obtained by this DPPA method.KEY WORDSDiphenylphosphoryl azide (DPPA) has been used as a convenient reagent for racemization-free peptide synthesis since it was synthesized by Shioiri eta!. in 1972. 1 It is non-explosive and stable enough to be stored for a long time without decomposition.Recently, we reported that this reagent can also be used successfully for the polymerization of amino acids or peptides. 2 A polypeptide can easily be prepared by just stirring the solution or suspension of amino acid or peptide in a suitable solvent with DPPA and a tertiary amine such as triethylamine. Poly(amino acid)s such as poly(glycine), poly(Lalanine), poly(L-leucine), poly(y-benzyl L-glutamate), poly(e-benzyloxycarbonyl-L-lysine), poly(f3-alanine) and poly(6-aminohexanoic acid) were prepared by this method. 2 Sequential polypeptides such as poly( -alanylglycyl-L-histidyl-[3-alanylglycine), and poly(f3-benzyl-L-aspartyl-f3-alanylglycyl-O-benzyl-L-seryl-f3-alanylglycyl-L-histidyl-f3-alanylglycine) were also synthesized successfully, as previously reported. 2 In particular, the polymerization of L-histidine-containing hexa-or nonapeptide gave a high-molecular-weight sequential polypeptide. Thus the DPPA method seems to have the possibility of becoming one of the very convenient and efficient methods for polypeptide synthesis, especially for the synthesis of sequential polypeptides, if the further exhaustive investigation is performed. In developing this method of polymerization, it would be very helpful to investigate in detail the relationship between the reaction conditions and results, using one kind of peptide as a representative.In the present study, the polymerization of Lalanylglycine was investigated in detail to find the most suitable reaction conditions for this peptide and, as a result, useful information by which this DPPA method could be used for the general synthesis of sequential polypeptides was obtained. The detailed s!udy on the composition or the purity of resultant poly(L-alanylglycine) are also reported. EXPERIMENTAL MeasurementsElemental analyses were carried out with a Yanagimoto CHN Corder, Model MT-2. Optical rotations were measured with a Yanagimoto 183