Abstract
Tow new antitumor antibiotics, AX-1 (3) and AX-2 (4), were isolated from the culture broth of streptomyces caespitosus, which is a mitomycin producing microorganisum, as a colourless crystals and yellowish orange powders, respectively. They have the same molecular formula of C_<16>H_<19>N_3O_6, which is also same to that of mitomycin A (1). Their structures were elucidated as shown in Fig. 1, on the basis of detailed NMR experiments including long range selective proton decoupling (LSPD) techniques. AX-1 (3) has a novel pentacyclic ring system, the formation of which would be explained to be an intramolecular adduct formed by Michael-type addition of the aziridine nitrogen to C-4a in the quinone moiety. AX-2 (4) would be the product formed through a cleavage of the bond between C-4a and N-4 by a retro-Michael reaction. Indeed, both compounds were found in the solution of mitomycin A (1), after standing it for several hours. This unique Michael reaction, named mitomycin rearrangement,is promoted by Lewis acids. The correspondind analogue, CX-1 (5), was also derived from mitomycin C (2) and isolated in 3% yield. The antitumor activity of the new compounds will be reported.
