A major problem in polypeptide synthesis is the formation of products with a wide range of molecular weights. As a step toward the total synthesis of natural protein, an attempt was made to synthesize a sequential polypeptide with a defined molecular weight. Thus, poly-(L-prolyl-L-prolylglycyl) with ten or twenty repeating units was synthesized by the step-by-step addition of AOC-L-prolyl-L-prolylglycine (I)1) using the solid-phase procedure.2) The synthesis was started from glycine-anchored polystyrene (100-200 mesh, copolymerized with 2% divinylbenzene; 14g, 0.1mmol/g), to which AOC-L-prolyl-L-proline (1.4g)1) was coupled in methylene chloride with dicyclohexylcarbodiimide. The AOCgroup was then removed with 2N hydrogen chloride in acetic acid, and the tripeptide-cycle was extended with I (1.7g per cycle) and dicyclohexylcarbodiimide (0.9g per cycle); each coupling reaction was carried out in methylene chloride for 3hr at room temperature. After nine reaction cycles, when ten repeating units were expected to have been formed, a part of the resin was dried (wt 7g) and placed in an HFreaction cylinder;3) anisole (7ml) was added, and then anhydrous hydrogen fluoride (HF, was introduced over the resin by means of the HFexcess HF was removed, and the peptide liberated was extracted with water. The water extract was treated with IR-45 (OH-form), and then dialyzed against distilled water for 3 days. The final solution was lyophilized (II, wt 0.

SynopsisSequeliced polytripeptides, (Pro-Pro-Gly),, ( n = 10, 15, 20), with defined molecular weights were sytithesized by the solid-phase method. Cotiformatioiial changes of these samples as a futictiori of temperatiire were studied by rnrasriremetits of optical rotation and redimeritatioti equilibrium. The temperature dependelice of opt,ical rotation was shown similar to thermal transition of collagen moleciile. Each of these polymers existed as a trimer a t lower temperature. (Pro-Pro-Gly),, existed as a monomer a t higher temperature, and the others were expected to behave analogously. 415

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