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The electron density distribution (EDD) of a plant cyclic nonapeptide of orbitide type was studied. Crystal X-ray diffraction data was obtained from the Cambridge Structural Database (CSD) and refitted using scattering factors of the invariom library, thereby providing aspherical electron density. Bond topological, atomic properties and molecular surfaces (electrostatic potential and Hirshfeld surfaces) were derived. The partial double bond character of the peptide bond was confirmed by the ellipticity ε= 0.25. For eight N–H⋯O hydrogen bonds, atomic charges of contributing atoms differ depending on the type of the accepting oxygen atom. Atomic charge differences between negative main and positive side chains of this nonapeptide result in characteristic features of the electrostatic potential, which shows a positive isosurface around the molecule leading to repulsive interactions in the solid state structure. Weak intermolecular interactions are indicated by insignificant ED concentrations on the Hirshfeld surface except for weak signals at sites of intermolecular N–H⋯O and C–H⋯O hydrogen bonds.

The title compounds have raised considerable medical and broad public interest in that sildenafil is used as an agent against male erectile dysfunction; iso-sildenafil is not in clinical use. A comparison of their structural and electronic properties therefore seems of interest. The electron densities of iso-sildenafil and the cationic and neutral forms of sildenafil were examined by the application of the invariom formalism relying on diffraction data reported in the literature. The electron-density distributions obtained were subjected to topological analysis using the quantum theory of atoms in molecules (QTAIM) formalism to yield bond topological and atomic properties. Moreover, molecular Hirshfeld surfaces and electrostatic potentials (ESPs) were calculated. A number of structural and electronic differences were thus identified between sildenafil and the iso-analog. In both sildenafil structures, the phenyl ring and the pyrazolopyrimidine fragment are practically coplanar (planar conformation), whereas in the iso-analog they exhibit an angle of 44° (inclined form). Related to differences in molecular structure are completely different hydrogen bonding patterns and differences in the ESPs, the latter ones being influenced by different methylation at the pyrazolopyrimidine fragment. Iso-sildenafil is present as a hydrogen-bond dimer in the crystal, and the ESP of this dimer is dominated by a surrounding positive potential.

A mixture of two compounds with potent antiplasmodial activity in vitroagainst the W2 strain of Plasmodium falciparum(half maximal inhibitory concentration, 1.12 μg/mL) was obtained in a previous investigation of the CH2Cl2-MeOH extract of the seeds of Salacia longipesvar. camerunensis.Separation by column chromatography led now to the isolation of salaterpene E (1) and (1R,2R,4S,5S,6R,7R,9S,10R)-2-acetoxy-1,6,9-tribenzoyloxy-4-hydroxy-dihydro-β-agarofuran (2). The structure of 1was elucidated by spectroscopic analysis, and its absolute configuration was established unambiguously by means of single-crystal X-ray diffraction. Also the absolute configurations of the recently described salaterpenes A (2a) and D (2b) were determined by this method using the anomalous scattering of the oxygen atoms only.

Phytochemical investigation of the roots and fruits of Mitragyna inermis (Rubiaceae) resulted in the isolation of a new indole alkaloid, named naucleactonin D (1), together with fourteen known compounds: nauclefiline (2), naucleficine (3), nauclefidine (4), angustoline (5), angustine (6), barbinervic acid (7), quinovic acid 3-O-a-L-rhamnopyranoside (8), betulinic acid (9), a mixture of ursolic (10) and oleanolic acid (11), a mixture of stigmasterol and b-sitosterol, b-sitosterol 3-O- b-D-glucopyranoside, and strictosamide (12) as the major compound. The structures of the isolated compounds were elucidated by detailed spectroscopic analysis and by comparison with published data. No 13C NMR data for 2 and 3 exist in the literature and compounds 2, 3, 5, 7, and 12 are reported for the first time from the genus Mitragyna. The crude extract and isolated compounds were tested in vitro for their preliminary cytotoxicity against brine shrimps (Artemia salina).