Two stereoisomeric pentacyclic oxin­dole alkaloids from Uncaria tomentosa: uncarine C and uncarine E

The chloro­form solvate of uncarine C (pteropodine), (1′S,3R,4′aS,5′aS,10′aS)-1,2,5′,5′a,7′,8′,10′,10′a-octa­hydro-1′-methyl-2-oxospiro­[3H-indole-3,6′(4′aH)-[1H]­pyrano­[3,4-f]indolizine]-4′-carboxyl­ic acid methyl ester, C₂₁H₂₄N₂O₄·CHCl₃, has an absolute configuration with the spiro C atom in the R configuration. Its epimer at the spiro C atom, uncarine E (isopteropodine), (1′S,3S,4′aS,5′aS,10′aS)-1,2,5′,5′a,7′,8′,10′,10′a-octahydro-1′-methyl-2-oxospiro[3H-indole-3,6′(4′aH)-[1H]pyrano[3,4-f]indolizine]-4′-carboxylic acid methyl ester, C₂₁H₂₄N₂O₄, has Z′ = 3, with no solvent. Both form intermolecular hydrogen bonds involving only the ox­indole, with N⃛O distances in the range 2.759 (4)–2.894 (5) Å.