Monomethyl ethers of 4,5-dihydroxypipecolic acid from Petaladenium urceoliferum: Enigmatic chemistry of an enigmatic legume

Leaves of Petaladenium urceoliferum accumulate (2S,4R,5R)-4-hydroxy-5-methoxypipecolic acid (1) and the (2S,4S,5R) and (2S,4R,5S) epimers of 5-hydroxy-4-methoxypipecolic acid (2 and 3). These compounds were not detected in any of the other genera in the Amburaneae clade of legumes to which P. urceoliferum belongs.