Conformational Considerations in 1-Oxaquinolizidines Related to the Xestospongin/Araguspongine Family: Reassignment of Stereostructures for Araguspongines B and E
摘要:
Conformational aspects of the 1-oxaquinolizidine ring system found in the xestospongin/araguspongine family of natural products has been studied by molecular modeling and NMR spectroscopy. Stereochemical complexities [e.g., (i) cis- vs trans-decalin-like conformers and (ii) relative configuration of variously substituted 1-oxaquinolizidines] associated with this bridgehead nitrogen-containing skeleton are discussed. Experimental equilibrium values are rationalized. Reassignment of the stereostructures for araguspongines B (from 4 to 6) and E (from 5 to 2) is made in light of the above.