Research Article Thermal Synthesis of Polypeptides from N -Butyloxycarbonyl Oligopeptides Containing Aspartyl Residue at C-Terminus Toratane Munegumi 1 and Takafumi Yamada 2 1 Department of Science Education, Naruto University of Education, Naruto, Tokushima 772-8502, Japan 2 Department of Chemistry, University of Tsukuba, Tsukuba, Ibaraki 305-857, Japan Correspondence should be addressed to Toratane Munegumi; tmunegumi@naruto-u.ac.jp Received 4 January 2017; Revised 22 May 2017; Accepted 12 June 2017; Published 30 July 2017 Academic Editor: Peng He Copyright © 2017 Toratane Munegumi and Takafumi Yamada. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Te thermal reactions of amino acids have been investigated for pure organic synthesis, materials preparation in industry, and prebiotic chemistry. N-t-Butyloxycarbonyl aspartic acid (Boc-Asp) releases 2-butene and carbon dioxide upon heating without solvents. Te resulting mixture of the free molten aspartic acid was dehydrated to give peptide bonds. Tis study describes the thermal reactions of N-t-butyloxycarbonyl peptides (Boc-Gly-L-Asp, Boc-L-Ala-L-Asp, Boc-L-Val-L-Asp, and Boc-Gly-Gly-L-Asp) having an aspartic residue at the carboxyl terminus. Te peptides were deprotected upon heating at a constant temperature between 110 and 170 ∘ C for 1 to 24 h to aford polypeptides in which the average molecular weight reached 7800. 1. Introduction Polypeptides [1] have been well investigated as protein model compounds [1–8]. Numerous reports on the methodology for the synthesis of polypeptides have been published [1–14]. Te N-carboxyl--amino acid anhydride (NCA) method (1) [2, 3, 9, 10], polymerization of amino acids using active esters (2) [1, 4–7], solid-phase peptide synthesis (3) [8, 12], and the heating of amino acids (4) [13, 14] are typical examples. Te NCA method (1) is suitable for making homopolypeptides and random copolypeptides but is not suitable for the synthesis of sequential copolyamino acid, which is more important for the build-up of functional polypeptides. Sequential polyamino acids have repetitive amino acid residues, in which the amino acid residues can be like -(Gly-Gly-Asp)-. Te active ester method (2) [1, 4–7] and solid phase synthesis (3) [8] are more suitable for the synthesis of sequential copolyamino acid. However, the problems of methods (2) and (3) are a long reaction time and the use of much solvent. In contrast, the synthesis of polyamino acid by heating a derivative of the amino acid (4) [13, 14] requires neither long reaction time nor solvents. In previous papers [15, 16], we reported the synthe- sis of homopolypeptides [15] and random copolypeptides [16] upon heating of N-t-butyloxycarbonyl aspartic acid anhydride (Boc-Asp anhydride) and mixtures of Boc-L-Asp, anhydride, and Boc-Gly, Boc-L-Ala, or Boc-Val. In this paper, we report a trial for the synthesis of sequential copolypeptides by the heating of Boc-peptides instead of these anhydrides. As shown in Figures 1 and 2, Boc-peptides (5a–d) and Boc-L-Asp (5e) were prepared for heating under a stream of N 2 . 2. Materials and Methods 2.1. Instrumentation. A nuclear magnetic resonance (NMR) (JEOL FX-100 NMR system (JEOL, Tokyo, Japan)) was used for the collection of 1 H-NMR spectra. A Hitachi model 260-50 infrared (IR) spectrophotometer (Hitachi, Tokyo, Japan) was used for the collection of IR spectra. A Hitachi 200-10 spectrophotometer was used for spectrophotometry measurements. A Jasco DIP-181 digital polarimeter (Jasco, Tokyo, Japan) was used for the measurement of the optical rotation of the peptide derivatives. A Hitachi 163 gas chromatograph Hindawi International Journal of Polymer Science Volume 2017, Article ID 8364710, 16 pages https://doi.org/10.1155/2017/8364710