Porosin: A neolignan from Ocotea porosa

The wood of Ocotea porosa (Nees) L. Barr. (Lauraceae) contains sitosterol, sesquiterpenes, n-octacosanoic acid, n-hexacosanoic acid and the neolignan porosin for which the structure of 3a-allyl-5-methoxy-3-methyl-2-veratryl-2,3,3a,6,7,7a-hexahydro-6-oxobenzofuran (II) is proposed.     

Hexahydrobenzofuranoid neolignans from an Aniba species

The trunk wood of an Amazonian Aniba species contains three novel neolignans: (2R, 3R, 3aS, 5R)-3a-allyl-5-methoxy-2-(3,4,5-trimethoxyphenyl)-3-methyl-2,3,3a,4,5,6-hexahydro-6-oxobenzofuran (canellin-D), (2R,3R,3aS,5R)-3a-allyl-5,7-dimethoxy-2-(3-methoxy-4,5-methylenedioxyphenyl)-3-methyl-2,3,3a,4,5,6-hexahydro-6-oxobenzofuran (canellin-E) and (2S,3S,3aS,5R)-3a-allyl-5-methoxy-2-(3-methoxy-4,5-methylenedioxyphenyl)-3-methyl-2,3,3a,4,5,6-hexahydro-6-oxobenzofuran (armenin-C). The absolute stereochemistries of these and of all other known hexahydro-6-oxobenzofurans were determined by CD comparisons with model compounds.     

Structure of porosin

The reported structure of porosin, 3a-allyl-5-methoxy-3-methyl-2-veratryl-2,3,3a,6,7,7a-hexahydro-6-oxo-benzofuran, is revised with respect to Δ-4,5. ¹H NMR (LIS), UV and photochemical evidence shows that the double bond is located at the 7,7a-position.     

13C NMR spectroscopy of neolignans

The ¹³C NMR spectra of 15 neolignans of several structural types and two lignans were analyzed and their carbon shifts assigned. The shifts of pyrogallol ether and ethyl phenyl carbinyl ether models were used in this connection. The stereochemistry of a dimeric sideproduct in the preparation of the latter models was determined by ¹³C NMR analysis.