1-(1-Hy­droxy­eth­yl)-7,8-dihydro­indolo[2,3-a]pyridine­[3,4-g]quinolizin-5(13H)-one (angustoline) monohydrate from Nauclea subdita (Rubiaceae)

The title compound (trivial name: angustoline monohydrate), C(20)H(17)N(3)O(2)·H(2)O, features a fused-ring system formed by one five- and four six-membered rings. The nearly planar benzimidazole portion (r.m.s. deviation = 0.008 Å) and the nearly planar 2,7-naphthyridin-1-one portion (r.m.s. deviation = 0.022 Å) of the fused-ring system are slightly twisted, with a dihedral angle of 9.47 (8)°, owing to the tetra­hedral nature of the two methyl­ene linkages in the central six-membered ring. The secondary N atom acts as a hydrogen-bond donor to the water molecule of crystallization. In the crystal, the amino and hy­droxy groups, and the water mol­ecule are engaged in hydrogen bonding, generating a three-dimensional network.