Polyketides tricyclic

Figure 7.4 Structures of the polyacetylenes, falcarinol (10), and the tricyclic polyketide, anthrone (11).

Today, despite recent developments in combinatorial and other chemosynthetic strategies, flmgi and streptomycetes remain the most prolific sources of new candidate drugs and agrochemicals. Both phyla elaborate bicyclic, tricyclic and tetracyclic fused ring polyketides, however, a preliminary survey of isotopically labelled precursor incorporation studies has revealed a consistent difference in the modes of cyclisation by which their characteristic polybenzenoid metabolites are formed. These and subsequent observations (yide infra) provide the basis for a novel biosynthetic classification of microbial fused ring polyketides. 

Prorocentin (197), a C35 polyketide with four pendant methyl groups, possessing an all-trtfwrtriene moiety, an epoxide, a fnran ring, and the 6/6/6-trans-fused/spiro-linked tricyclic ether rings, was isolated from an okadaic acid-producing strain of P. The relative stereostructure was elucidated on the basis of spectral data. 

Name of colored hydroxynaphthoquinone derivatives with a tricyclic polyketide skeleton. For substitution on the dihydropyran ring there are two stereochemical series (A= actinorhodins, G= granaticins). B. are typical metabolites of streptomycetes, over 50 representatives are known which exhibit differing biological activities, including antibacterial, antifungal, anti-neoplastic, antiviral (also against HIV) actions. 

Some ants make products reminiscent of the coccinellid alkaloids. Three indolizidines are known from the venom gland of Monomorium pharaonis (Figure 9.10), and a pyrrolizidine from a Solenopsis ant has been known for some time. They would appear to be formed from polyketides or fatty acids as in the case of the coccinellines. More pyr-rolizidines and indolizidines with two alkyl and alkenyl groups have been found in Monomorium and Solenopsis species. Tetraponerine ants smear the venom of their poison glands onto prey. The venom consists of tricyclic alkaloids called tetraponerines (Figure 9.10). They are divided... 

The great structural similarity among the four basic types of cytochalasans known as present, i.e., the [11] cytochalasans, [13] cytochalasans, 24-oxa-[14]cytochalasans, and 21,23-dioxa-[13]cytochalasans, and the experimental evidence available, permit one to postulate a common biogenetic scheme for all cytochalasans. Such a scheme is shown in Fig. 15. The tricyclic systems, which result from the combination of the amino acid with a Ci6- or Cig-polyketide or a biogenetic equivalent, may be structures of a lower oxidation state. It also is unknown at what stage of the biogenetic sequence the introduction of the additional units takes place. 

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