4 生合成酵素の精密機能解析を基盤とする非天然型新規化合物の創出(口頭発表の部)

抄録

1. A C_<35> polyprene in which a farnesyl C_<15> unit is connected in a head-to-head fashion to a geranylgeranyl C_<20> unit was enzymatically converted to an unnatural hexacyclic polyprenoid by squalene: hopene cyclase from Alicyclobacillus acidocaldarius. The cyclization of the C_<35> polyprene was initiated by a proton attack on the terminal double bond of the C_<15> unit, and proceeded without rearrangement of carbon and hydrogen. The substrate should be folded in chair-chair-chair-chair-boat-boat conformation in order to achieve the stereochemistry of the cyclization product. 2. Substrate specificities of chalcone synthase (CHS) were investigated using analogs of malonyl-CoA, the extension unit of the polyketide chain elongation reactions. When incubated with methylmalonyl-CoA and 4-coumaroyl-CoA, CHS from Scutellaria baicalensis afforded an unnatural C_6-C_5 aromatic polyketide, 1-(4-hydroxyphenyl)pent-1-en-3-one, formed by one-step decarboxylative condensation of the substrates. In contrast, succinyl-CoA was not accepted as a substrate. Next, both the starter and the extension unit were simultaneously replaced with non-physiological substrates. When incubated with benzoyl-CoA and methylmalonyl-CoA, CHS afforded a novel triketide, 4-hydroxy-3,5-dimethyl-6-phenyl-pyran-2-one, along with a tetraketide, 4-hydroxy-3,5-dimethyl-6-(1-methyl-2-oxo-2-phenyl-ethyl)-pyran-2-one. On the other hand, the enzyme also accepted hexanoyl-CoA and methylmalonyl-CoA as substrates to produce an unnatural novel triketide, 4-hydroxy-3,5-dimethyl-6-pentyl-pyran-2-one.