The synthesis of methyl N-(2,2-dimethyl-2H-azirin-3-yl)-~-prolinate (3), a novel 3-amino-2H-azirine, is described (Scheme 2). It is shown that the reaction of COCI, with thioamide 5 is remarkably faster than with the corresponding amide 4, and the yield of 3 is much better in the synthesis starting with 5. The 3-amino-2H-azirine 3 has been used as a building block of the dipeptide moieties Aib-Pro in the synthesis of nonapeptide 17 (Schemes 4 and 9, the C-terminal 6-14 segment of the peptaibole trichovirin I 1B. The structure of 17 was established by single-crystal X-ray crystallography (Figs. 1 and 2

Dedicated to Professor Duilio Arigoni on the occasion of his 75th birthday According to the earlier published synthesis of the C-terminal nonapeptide of Trichovirin I 1B, Z-Ser( t Bu)-Val-Aib-Pro-Aib-Leu-Aib-Pro-Leuol (5), the complete tetradecapeptide Z-Aib-Asn(Trt)-Leu-Aib-Pro-Ser( tBu)-Val-Aib-Pro-Aib-Leu-Aib-Pro-Leuol (11b), a protected Trichovirin I 1B, has now been prepared by means of the −azirine/oxazolone method×. With the exception of the N-terminal Aib(1), all Aib residues were introduced by the coupling of the corresponding amino or peptide acids with 2,2-dimethyl-2H-azirine-3-(Nmethyl-N-phenylamine) (1a) and methyl N-(2,2-dimethyl-2H-azirin-3-yl)-l-prolinate (3a) as the Aib and AibPro synthons, respectively. Single crystals of two segments, i.e., the N-terminal hexapeptide Z-Aib-Asn(Trt)-Leu-Aib-Pro-Ser( t Bu)-OMe (23) and the C-terminal octapeptide Z-Val-Aib-Pro-Aib-Leu-Aib-Pro-Leuol (17), were obtained and their structures have been established by X-ray crystallography. Following the same strategy, the C-terminal nonapeptide of Trichovirin I 4A, Z-Ala-Val-Aib-Pro-Aib-Leu-Aib-Pro-Leuol (26), was also synthesized and characterized by X-ray crystallography.

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A New 3-Amino-2H-azirine as an Aib-Pro Synthon: Synthesis of the C-Terminal Nonapeptide of Trichovirin I 1B.-The chiral azirinylprolinate (S)-(V) is prepared and used as synthon for the dipeptide moiety aminoisobutyric acid-isovaline, used in the synthesis of a nonapeptide, which is the C-terminal 6-14 segment of the tetradecapeptide trichovirin I 1B, isolated from Trichoderma viride. -(LUYKX, R.; BUCHER, C. B.; LINDEN, A.; HEIMGARTNER, H.; Helv.