Biomimetic syntheses of polyketide aromatics from reaction of an orsellinate anion with pyrones and a pyrylium salt

Abstract

I EW Orsellinate anion (12) shows highly regioselective attack on pyrones (13), (22), and (M), and the products were simply converted into derivatives of the polyketides: toralactone (19), 6hydroxymusizin (26), and eleutherinol (32); although reaction of the anion (12) with the pyrylium salt (33) is less selective, the major product (34) can give derivatives of either alternariol (36) or rubrofusarin (37) in regiospecific biomimetic reactions.

Polyketide biosynthesis: a millennium review

“…19 Several other groups used pyrone chemistry to generate transient intermediates with polyketone chains. [20][21][22] The researchers were motivated by the idea that enzymatic control in vivo might be achieved by selection of the folding point of the chain so that the first carbocyclic ring is formed at the appropriate site. The preferred mode for subsequent cyclisations would then be progressive formation of extra six-membered rings until a linear polycyclic system is generated.…”

“…61,62 Fig. 20 Examples of macrolide polyketides for which the genes have been sequenced in whole or in part.…”

Chromanols, chromanones, and chromones

“…It has also been isolated from the leaves of the related species Cassia multijuga (the ethanol extract of which possesses antibacterial activity) along with the 0-and Cglycosides ( 91) and (92); this work was published twice. 51 The identity of the sugar moiety of (92) was not determined, but a later report5' described the isolation from the seeds of Cassia spectahifis of a chromone which was assigned the structure (93). Hydrolysis of this material gave a compound that was said by the authors to be identical to (92); the method by which the sugar moiety of (92) was determined to be D-glucose was not divulged.…”

“…85 92 and was recently synthesized in a short, possibly biomimetic, sequence, starting with the addition of the anion of methyl orsellinate dimethyl ether (166) to the pyrilium salt (167). 93 Naphthopyrones have been isolated from various marine organisms, often in the form of sulphate esters. Thus the crinoid Cornantheria perplexa was found to contain comantherin sulphate (168) and the homologue neocomantherin sulphate (169); the antifeedant effect of these compounds on fish may be an indication of their involvement in chemical defence processes.…”

“…The biosynthetic sequence that is shown in Scheme 4 was suggested, the chemical feasibility of such a pathway having been demonstrated earlier. 93 and it has been suggested that an increase in the production of angular naphthopyranones with increasing age of the organism may be occurring in some cases.96 Eleutherinol dimethyl ether (1 81) has been synthesized efficiently via conjugate addition of the anion (166) to the y-pyrone (182), followed by c y ~l i z a t i o n . ~~…”