Papyracillic acid

Papyracillic acid B (203), isolated from an endophytic fungus Microsphaeropsis sp., is a penicillic acid analog containing a spirofused cyclic ketal core appended with an exocychc aUcene [111]. Very recently, its racemic synthesis has been achieved by Zercher et al. [112] via a Zn-carbenoid-mediated chain extension-acylation reaction (Scheme 1.32). At the last step of Zercher s synthesis, paparyciUic acid is obtained as 1 1 epimeric mixture with its C4 epimer, probably through an epimerization facilitated by exocyclic methylene group. 

---