Enantioselective Synthesis of (−)-Terpestacin and Structural Revision of Siccanol Using Catalytic Stereoselective Fragment Couplings and Macrocyclizations
Enantioselective Synthesis of (−)-Terpestacin and Structural Revision of Siccanol Using Catalytic Stereoselective Fragment Couplings and Macrocyclizations
作者:Johann Chan、Timothy F. Jamison
DOI:10.1021/ja0470968
日期:2004.9.1
(-)-Terpestacin (1, naturally occurring enantiomer) and (+)-11-epi-terpestacin (2) were prepared using catalyst-controlled, stereoselective, intermolecular reductive coupling reactions of alkyne 9 and aldehyde 10, affording allylic alcohols 42 or 11-epi-42 in a 3:1 ratio (or 1:3 depending on the enantiomer of ligand 41a used). These stereoselective fragment couplings were instrumental in confirming that "siccanol" is not 11-epi-terpestacin but, in fact, is (-)-terpestacin itself. Several intramolecular alkyne-aldehyde reductive coupling approaches to 1 and 2 were also investigated and are discussed herein.
The structure of siccanol, a phytotoxic sesterterpene of fungal origin, was analyzed after chemical conversion by NMR spectroscopy. Siccanol was found to be an epimer of terpestacin that has been isolated from Arthrinium sp., and was thus renamed 11-epiterpestacin. Its stereochemistry was also identical with that of fusaproliferin, a structurally related mycotoxin from Fusarium proliferatum. Therefore, this sesterterpene may also be referred to as 24-deacetyl fusaproliferin. The phytotoxicity of 11-epiterpestacin was almost equal to that of terpestacin, but significantly higher than that of fusaproliferin.