Direct Oxa-Pictet−Spengler Cyclization to the Natural (3a,5)-<i>trans</i>-Stereochemistry in the Syntheses of (+)-7-Deoxyfrenolicin B and (+)-7-Deoxykalafungin
作者:Clark N. Eid、Jaechul Shim、Jack Bikker、Melissa Lin
DOI:10.1021/jo801945n
日期:2009.1.2
The pyranonaphthoquinones (+)-7-deoxyfrenolicin B and (+)-7-deoxykalafungin were synthesized in four steps using an oxa-Pictet-Spengler cyclization that directly provided the natural (3a,5)-trans-substituted dihydronaphthopyrans with high diastereoselectivity. This outcome is in contrast to the unnatural (3a,5)-cis-substituted dihydronaphthopyrans reported under similar conditions for the syntheses of (+)frenolicin B and (+)-kalafungin. Computational modeling is presented that provides insight into this unusual stereoselectivity.
The syntheses of (±)-juglomycin A and (±)-juglomycin B, racemates of two isomeric naturally occurring naphthoquinonoid antibiotics
作者:Robin G. F. Giles、Peter R. K. Mitchell、Gregory H. P. Roos、Jacobus M. M. Strümpfer
DOI:10.1039/p19810002091
日期:——
Syntheses of the diastereoisomeric 5-hydroxy-2-(4′-hydroxy-γ-butyrolacton-5′-yl)-1,4-naphthoquinones (1) and (2) and their 5-deoxy-analogues (3) and (4) are described. The stereochemistries of the latter, being defined through unambiguous synthesis, permit the assignment of the configurations of (1) and (2)(which were obtained from a single precursor) and also those of the natural products, juglomycins