Rauniticine-allo-oxindole B methanol monosolvate

The title pentacyclic oxindole alkadoid, isolated from Uncaria longiflora, crystallizes as a methanol solvate, C20H22N2O4·CH4O. The five-membered ring comprising the indole fused ring is nearly planar [maximum atomic deviation = 0.031 (2) ], whereas the five-membered ring having alphatic C atoms adopts an envelope shape (with the tertiary N atom representing the flap). The six-membered ring that shares an N atom with the envelope-shaped ring adopts a chair shape; the six-membered ring having an O atom is sofa-shaped. The carboxylic acid group acts as a hydrogen-bond donor to a methanol molecule; this, in turn, acts as a hydrogen-bond donor to the double-bond carboxyl O atom of an adjacent molecule, generating a chain. Adjacent chains are linked by N—H...O hydrogen bonds, forming a layer motif.