Total synthesis of (+)-elacomine and (-)-isoelacomine, two hitherto unnamed oxindole alkaloids from Elaeagnus commutata

Racemic elacomine ((+/-)-2), a hemiterpene spiro oxindole alkaloid from Elaeagnus commutata, was synthesized in five steps from 6-methoxytryptamine (19) in 16% overall yield (Scheme 3). The final oxidative rearrangement of the corresponding beta-carboline precursor (+/-)-21 furnished isoelacomine ((+/-)-22) as a by-product (6% overall yield). A more elaborate route that started from L-tryptophan furnished (+)-2 and (-)-22 with optical purities of 76% (Scheme 4) and established the absolute configuration of these compounds. A reinvestigation of the alkaloidal content of the roots of E, commutata showed that both elacomine and isoelacomine occur naturally in racemic form.