ing an exo-type dimer of an isooxazoline ring like aerothionin 29 [59,60]. Recently, however, zamamistatin has been re-isolated and its structure has been revised [61]. A dihydro-1, 2-oxazine methyl ester 30 and a isoxazo-line methyl ester 31 [62] were synthesized as model compounds. The spiro-carbon signal (C-6) for 30 and 31 appeared at SC 92.4 and 79.9, respectively, while the carbon signal in the natural compound appeared at SC 74.3. Thus, the structure of natural zamamistatin has been revised to be 27, an endo-type dimer of an aza-oxa-spiro[6.6] unit possessing a dihydro-1,2-oxazine ring moiety.

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