147438-29-7Relevant articles and documents
Selective epimerization of rapamycin via a retroaldol/aldol mechanism mediated by titanium tetraisopropoxide.
Yang,Digits,Hatada,Narula,Rozamus,Huestis,Wong,Dalgarno,Holt
, p. 2033 - 2035 (1999)
We describe the efficient and selective epimerization of the immunosuppressant rapamycin to 28-epirapamycin under mild conditions. The mechanism of epimerization involves an equilibrium of the four C28/C29 diastereomers through a two-step retroaldol/aldol (macrocycle ring-opening/ring-closing) sequence. This retroaldol/aldol equilibration is not restricted to rapamycin but is also applicable to acyclic beta-hydroxyketones. A potentially useful extension of the method--the use of beta-hydroxyketones as enolate synthons for effecting inter- or intramolecular aldol reactions under neutral conditions--is demonstrated.
