Three new dihydro-β-agarofuran sesquiterpenes from the seeds of Maytenus boaria

As part of a project studying the secondary metabolites extracted from the Chilean flora, we report herein three new β-agarofuran sesquiterpenes, namely (1S,4S,5S,6R,7R,8R,9R,10S)-6-acetoxy-4,9-dihydroxy-2,2,5a,9-tetramethyloctahydro-2H-3,9a-methanobenzo[b]oxepine-5,10-diyl bis(furan-3-carboxylate), C₂₇H₃₂O₁₁, (II), (1S,4S,5S,6R,7R,9S,10S)-6-acetoxy-9-hydroxy-2,2,5a,9-tetramethyloctahydro-2H-3,9a-methanobenzo[b]oxepine-5,10-diyl bis(furan-3-carboxylate), C₂₇H₃₂O₁₀, (III), and (1S,4S,5S,6R,7R,9S,10S)-6-acetoxy-10-(benzoyloxy)-9-hydroxy-2,2,5a,9-tetramethyloctahydro-2H-3,9a-methanobenzo[b]oxepin-5-yl furan-3-carboxylate, C₂₉H₃₄O₉, (IV), obtained from the seeds of Maytenus boaria and closely associated with a recently published relative [Paz et al. (2017). Acta Cryst. C73, 451-457]. In the (isomorphic) structures of (II) and (III), the central decalin system is esterified with an acetate group at site 1 and furoate groups at sites 6 and 9, and differ at site 8, with an OH group in (II) and no substituent in (III). This position is also unsubstituted in (IV), with site 6 being occupied by a benzoate group. The chirality of the skeletons is described as 1S,4S,5S,6R,7R,8R,9R,10S in (II) and 1S,4S,5S,6R,7R,9S,10S in (III) and (IV), matching the chirality suggested by NMR studies. This difference in the chirality sequence among the title structures (in spite of the fact that the three skeletons are absolutely isostructural) is due to the differences in the environment of site 8, i.e. OH in (II) and H in (III) and (IV). This diversity in substitution, in turn, is responsible for the differences in the hydrogen-bonding schemes, which is discussed.

A dihydro-β-agarofuran sesquiterpene from Maytenus boaria

The natural compound (1S,4S,5S,6R,7R,8R,9R,10S)-6-acetoxy-4,9,10-trihydroxy-2,2,5a,9-tetramethyloctahydro-2H-3,9a-methanobenzo[b]oxepin-5-yl furan-3-carboxylate, C₂₂H₃₀O₉, (I), is a β-agarofuran sesquiterpene isolated from the seeds of Maytenus boaria as part of a study of the secondary metabolites from Chilean flora. The compound presents a central structure formed by a decalin system esterified with acetate at site 1 and furan-3-carboxylate at site 9. The chirality of the skeleton can be described as 1S,4S,5S,6R,7R,8R,9R,10S, which is consistent with that suggested by NMR studies. Unlike previously reported structures of sesquiterpenes containing a pure dihydro-β-agarofuran skeleton, (I) exhibits a three-dimensional hydrogen-bonded network.