The metabolism of phytoalexins

The biosynthesis of C5—C20terpenoid compounds

“…The biosynthesis of rishitin (36) from solavetivone (33) uia lubimin (34) and 3hydroxylubimin (35) (see Scheme 6) has been e ~t a b l i s h e d ~~ on the basis of feeding experiments with [8,8-2H2]solavetivone. A similar hydride shift (see Scheme 7) has been e ~t a b l i s h e d ~~ in the biosynthesis of PR toxin (37) alliaceus, suggest that its carbon skeleton can be dissected46 into isoprene units as shown in (40). Feeding experiments with [2-2H3]acetate and [2,2-2H2]-, [4,4-2H2]-, and [5,5-2H2]mevalonate revealed47 the occurrence of hydrogen rearrangements to C-1 and from C-5 to C-6 during the biosynthesis.…”

“…The production and metabolism of sesquiterpenoid phytoalexins has been reviewed. 40 Oxygen-18 studies have shown41 that all three oxygen atoms of ipomeamarone (32), produced by Ipomoea batatas, are derived from molecular oxygen and not water. The postulated migration of hydrogen from C-5 and C-4 in the biosynthesis of the potato phytoalexins lubimin, 3hydroxylubimin, and rishitin has been confirmed42 by the incorporation of [2-2H3, 2-I3C]acetate and direct observation of the predicted 0-shift of the I3C n.m.r.…”

Phytoalexins

“…6 Potato (Solanum tuberosum) Full papers have appeared on the isolation and identification of rishitinone (71)65 and of epilubimin (72), epioxylubimin (73), and isolubimin (74),66 all of which were isolated (as minor stress metabolites) from diseased potato tubers. Acetyldehydrorishitinol (75) was isolated from slices of potato tuber that had been treated with a cell-free extract from Phytophthoru injestans and incubated in an atmosphere of 10 pl of ethylene per litre of oxygen. The compound occurred at 40 ng per gram of fresh weight, with larger amounts of the usual potato phytoale~ins.~7 The new vetispirane derivatives (76) and (77) have been isolated from potato tubers that were infected with Phomu exiguu:68u the 3-deoxy-analogue (78) of the latter compound had already been isolated from the same source.68b…”

“…This is the first instance of (-)pisatin occurring as a natural product.' 75 The pterocarpan phytoalexin apiocarpin (207) was isolated from Apios tuberosa that had been challenged with H. carbonum.…”