Structure Elucidation and Synthesis of Stilbenolignans

The structures of stilbenolignans, elucidated almost exclusively by spectroscopic analysis, have often been confirmed through synthesis. The structure determination of a few important stilbenolignans together with their symtheses will be discussed in this section. It is pertinent to mention in this coimection that different numbering 

Kinghorn and coworkers reported the isolation and characterization of aiphanol (138), the only stilbenolignan having a dioxane bridge 149). Aiphanol (138), 

Kuboki and colleagues (756) reported a total synthesis of ( )-138 following a strategy developed by Pan et al. 141) for the synthesis of ( )-sinaiticin (96). 

The key intermediate for this synthesis was an aromatic aldehyde, linked with sinapyl alcohol (156) through a dioxane bridge. The aldehyde 166, on treatment with the appropriate phosphonium salt, yielded the desired stilbene. The essential steps of the preparation of the intermediate are summarized below. 

An enantioselective total synthesis of (—)-138 was also achieved using (1R,2R)-1 -(3, 5 -dimethoxy-4 -methoxymethoxyphenyl)-2,3-dihydroxypropanol, the absolute stereochemistry of which was confirmed by single-crystal X-ray analysis of a readily available bromo- derivative. It was proved to have the (5)-configuration at both the 7 and 8 positions (757). 

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