A New Antimicrobial Phenylpropanol from the Leaves of Tabernaemontana inconspicua Stapf. (Apocynaceae) Inhibits Pathogenic Gram-Negative Bacteria.

A chemical investigation of the leaves of Tabernaemontana inconspicua Stapf. led to the isolation of a new phenylpropanol derivative, namely irisdichototin G ( 1 ), together with nine known compounds, including one polyol derivative, dambonitol ( 2 ); three alkaloids, 10-hydroxycoronaridine ( 3 ), voacristine ( 4 ) and vobasine ( 5 ); two triterpenes lupeol ( 6 ), betulinic acid ( 7 ) and three sterols, sitosterol ( 8 ), sitosterol-3-O-β-D-glucopyranoside ( 9 ) and stigmasterol ( 10 ). The structure of the new compound, as well as those of the known ones, was established by means of spectroscopic methods: NMR analysis ( 1H and 13 C NMR, 1H-1H-COSY, HSQC, HMBC and NOESY), high-resolution mass spectrometry (HR-ESI-MS) and comparisons with previously reported data. Among the known compounds, compound 2 was firstly reported from the family Apocynaceae. Compounds 1 - 5 were tested for their antimicrobial effects against three Gram-negative organisms associated with human wound and systemic infections, namely Haemophilus influenzae 9435337A, Klebsiella pneumoniae 17102005 and Pseudomonas aeruginosa 2137659B. Compounds 1 , 3 , and 5 showed significant antimicrobial effects with minimum inhibitory concentrations (MIC) of 62.5 μg/mL, 62.5 μg/mL and 7.81 μg/mL, respectively, against Haemophilus influenzae , whereas compounds 1 and 5 showed significant antimicrobial effects, with a MIC value of 31.25 μg/mL against Pseudomonas aeruginosa . In addition, compound 3 showed significant antimicrobial activity, with a MIC value of 31.25 μg/mL against Klebsiella pneumoniae .