Biosynthesis of Phytotoxins fromAlternaria solani

Biosynthesis of lovastatin and related metabolites formed by fungal iterative PKS enzymes

“…When this ratio was corrected for the amount of cyclization that occurs spontaneously in aqueous solution, it was found that the enzyme produces the exo adduct (solanapyrone A) and the endo adduct (solanapyrone D) in a ratio of 87 to 13, which is the opposite selectivity of the noncatalyzed reaction. The reduced solanapyrones B and E were not detected in any of these experiments and it is thought that these are formed downstream of solanapyrones A and D 14, 60…”

“…The first solanapyrones (A, B, and C) that were discovered were isolated from Alterna solani 55 and another ten have been isolated 56–59. This class of compounds was the first shown to utilize a Diels‐Alderase in their biosynthesis,60 and to incorporate diene and dienophile precursors into natural products 61. Feeding experiments with labeled sodium acetate and methionine showed that the backbone of solanapyrones are biosynthesized by a PKS, which condenses eight acetate units in a head to tail fashion and transfers two methyl groups,62 to produce the octaketide, prosolanapyrone II (see Figure 8).…”

“…No transformation occurred, but upon exposure to oxygen, activity was recovered. To examine whether the Diels‐Alder reaction could occur spontaneously, prosolanapyrones II and III were synthesized and transformations were studied both with and without enzymatic extracts 60, 64. In aqueous solution, prosolanapyrone II was not observed to undergo a cycloaddition; however, when it was added to the enzyme extract, 25% of it reacted to form 6% prosolanapyrone III and 15% of the exo and endo cycloaddition solanapyrone adducts, A and D, in a ratio of 85 to 15, respectively.…”

Functional analysis of fungal polyketide biosynthesis genes

“…Of these, alternaric acid was indicated to be biosynthesized from two polyketide chains rather than a single chain. 42 Alternaria solani also produces other complex reduced-type polyketides, solanapyrones. [43][44][45] Biosynthetic studies strongly suggested that a biological Diels-Alder reaction is involved in formation of their decalin skeleton.…”

Expression of Alternaria solani PKSF Generates a Set of Complex Reduced‐Type Polyketides with Different Carbon‐Lengths and Cyclization

“…No MeT domain (present in LNKS, LDKS, [11] and PKSN [8] ) was identified in either PKSF or PKSK. The A. solani metabolites solanapyrone and alternaric acid both contain methionine-derived methyl branches, [12] so neither PKSF nor PKSK could be the PKS responsible for these compounds.…”