360ChemInform Abstract The structure of the title compound, the major component of the calichemicin complex (isolated from Micromonospora echinospora ssp. calichensis and known as LL-E33288 antibiotics) is investigated in part by chemical (derivatization, degradations etc.) and physical methods. It can be shown that the title compound consists of four glycosidic units, a hexasubstituted benzene moiety and an undefined C18H16NO4S3 unit. The exact configuration of the ethylamino sugar is unknown. In the following paper the structure of the undefined aglycone is reported.

361ChemInform Abstract Further chemical and physical investigations on the structure of the title compound, in addition to the results of the preceding paper, establish its complete structure as (I).

Section. His research Interests are focused on natural products chemistry, drug/DNA Interactions, and mechanisms of antibiotic activity. Donald B. Borders Is the Department Head for the Microbial Chemistry Department In the Medical Research Division of American Cyanamid. He was bom In 1932 In Logansport, IN. He received a B.S. (1954) and M.A. (1958) In chemistry from Indiana University and a Ph.D. (1963) In Organic Chemistry from the University of Illinois (with K. L. Rinehart). From 1962 to 1964 he was a research chemist for Rohm and Haas Company and then Joined Lederle Laboratories, a Division of American Cyanamid. His research Interests have been In the Isolation, structure determination, and biosynthesis of natural products.

The biosynthetic origin of the carbon atoms in the chromophores of chrysomycins A and B was investigated in feeding experiments using 13C labeled acetates and propionate.A biosynthetic scheme is proposed involving the condensation and rearrangement of a decaketide intermediate which contains either propionate (chrysomycin A) or acetate (chrysomycin B) as the chain initiator.The isolation of chrysomycin was first reported in 1955 by STRELITZ and coworkers1) who were screening for antibiotics with activity against bacteriophages.Although the physico-chemical properties of this antibiotic, including a highly characteristic absorption spectrum, were published, no structure was established. Subsequently, several related antibiotics containing very similar, if not identical, chromophores were described: toromycin2), virenomycin3), gilvocarcin4) and ravidomycin5)'.The first member of this group of related antibiotics to have its structure determined was toromycin6), which was shown to consist of a substituted naphthalene chromophore with a sugar moiety attached by a carbon-carbon glycosyl bond. Structures for other members of this group quickly followed7~9), and all contained the same tetracyclic chromophore. Gilvocarcin V proved to be identical to toromycin as also did other antibiotics'10~12). Although a detailed comparison has not been possible, it seems likely that virenomycin has the same structure as chrysomycin. Both chrysomycin and gilvocarcin occur in microbial fermentations as a mixture of two analogues that differ only in having a vinyl (chrysomycin A and gilvocarcin V) or methyl (chrysomycin B and gilvocarcin M) substituent on the chromophore. In the case of ravidomycin only the vinyl analogue has been described. The structures of chrysomycin, gilvocarcin and ravidomycin are shown in Fig. 1. Although toromycin is the preferred name for 3, the only biosynthetic studies reported for this compound were done using Streptomyces gilvotauareus13), hence in this paper we refer to this antibiotic as gilvocarcin V. Recently we reported on the biosynthesis of ravidomycin14) and proposed a scheme in which a single decaketide chain initiated by propionate gave rise to the chromophore via a tetracyclic intermediate from which two carbons are lost. TAKAHASHI and TOMITA13) have published results on the biosynthesis of gilvocarcins V and M, and proposed a scheme that differs significantly from that for ravidomycin. The key difference between the two biosynthetic schemes concerns the C-8 vinyl substituent. In the case of ravidomycin, it derives from propionate, which is suggested to be a polyketide chain initiator and retains its carboxyl as part of the chromophore. Although the gilvocarcin scheme also proposes a propionate origin, it is a secondary substituent added to a pre-existing ring system with loss of its associated carboxyl group. According to this latter scheme gilvocarcin M was synthesized by substituting the chromophore with acetate rather than propionate, again with concomitant loss of the carboxyl group.

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