The structure of biyouyanagin A (1, Fig. 1), a natural product isolated from the leaves of H. chinense L. var. salicifolium, and specifically its stereochemistry at the C-24 position had not yet been completely characterized. In view of this remaining ambiguity, Nicolaou and coworkers synthesized and elucidated the structures of both the 24S (2a) and 24R (2b) epimers (2, Fig. 1). Epimers 2a and 2b were synthesized in 12 steps from dienes 3a or 3b and hyperolactone 4. Dienes 3a and 3b were prepared from (S)- and (R)-citronellals 5a and 5b, respectively (Scheme 1), whereas hyperolactone C (4) was accessed from L-malic acid (Scheme 2). Dienes 3a and 3b underwent an unprecedented [2+2] cycloaddition reaction with lactone 4 under triplet-sensitized irradiation condition (Scheme 3). The cycloaddition reaction proceeded in a rapid chemo-, regio-, and stereoselective manner. The spectroscopic data of 2b were consistent with those of the natural product (Table 1). However, NOE data of biyouyanagin A showed that there is no strong interaction between H18 and the closest protons on the aromatic ring. This result supports structure 2b rather than the originally proposed structure 1b. In view of this, the researchers have reassigned the full stereochemistry of biyouyanagin A from 1a or 1b to 2b.
|Original language||English (US)|
|Number of pages||5|
|State||Published - Feb 1 2008|
ASJC Scopus subject areas
- Molecular Biology