Lanthanide shift reagents in neolignan analysis: Revision of structure of canellin-B

PMR studies using lanthanide shift techniques showed that the constitution of canellin-B must be revised to rel-(2S,3S,3aS,5S)-3a-allyl-5,7-dimethoxy-3-methyl-2-piperonyl-2,3,3a,4,5,6-hexahydro-6-oxobenzofuran and that the previous assignments of H-2, H-4 and H-7 signals of some other benzofuranoid neolignans must be interchanged. The isolation of 5-methoxyguianin from Licaria canella (Meissn.) Kosterm. and the characterization of (2R,3S,5R)-5-allyl-5-methoxy-3-methyl-2-piperonyl-2,3,5,6-tetrahydro-6-oxobenzofuran from Aniba terminalis Ducke is also reported.