5526product mixtures were formed on irradiation. Small amounts of products with short retention times were observed, but these materials did not accumulate sufficiently to allow isolation. Addition of acetic acid after irradiation did not lead to any new product peaks.A preparative scale photolysis was carried out on 0.76 g of 17 in 100 ml of nitrogen-purged tert-butyl alcohol. After irradiation for 24 hr, the solvent was removed in vacuo and the residue was subjected to preparative gc (B, 180"). The major product (0.10 g) appeared to be a mixture of cyclobutanols as evidenced by the presence of hydroxyl absorptions in the infrared spectrum at 2.90 I J : nmr 6 1.21 ( s ) and 1.40 (s); mass spectrum mle (re1 intensities) 180 (1 I), 162 (38), 122 (loo), 43 (8 1). Abstract: Syntheses are described of three N-benzyloxycarbonylpeptide tert-butoxycarbonylhydrazides which correspond to positions 12-23, 24-34, and 3547, respectively, of the proposed primary structure of the enzyme ribonuclease TI. Evidence is presented to indicate that these materials are sequentially homogeneous. These fragments were condensed to form an N-benzyloxycarbonylhexatricontapeptide tert-butoxycarbonylhydrazide corresponding to positions 12-47 of the primary sequence of the enzyme. Available techniques to evaluate homogeneity of complex peptides are critically discussed and the concept of "diagnostic" amino acid residues is introduced.ibonuclease TI [ribonucleate guanine nucleotido-2'- Preparation of Fragments B, C, and DDoubly protected peptide hydrazides, such as fragments B, C, and D , are desirable intermediates for con-

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Spectroscopic studies of alternating polypeptides, prepared by polymerizing dipeptides containing one l and one d residue, indicate that in helicogenic solvents they adopt conformations with properties different from those of the normal a helix. The properties of such polypeptides in which polymerization has been accompanied by appreciable racemization are similar to those of poly(L-aspartic esters), and a distorted type of a helix is suggested; when racemization is negligible a new conformation, the nature of which is uncertain, appears to be formed. This paper is concerned primarily with the conformations adopted in solution by "alternating" sequential polypeptides of the type H-f AB^-"OH, where A and B are amino acid residues which give rise to poly(amino acids), HA"OH and HB"OH, with -helical conformations of opposite sense