Photosensitizing anthraquinones from Heterophyllaea lycioides (Rubiaceae)

JOSE L. CABRERA; JESICA A. DIMMER , JOSE L. CABRERA; CATERINE S. MENDOZA; SUSANA C. NÚNEZ MONTOYA

PHYTOCHEMISTRY

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2017 vol. 137 p. 94 - 100

0031-9422

Seven anthraquinones were isolated from aerial parts of Heterophyllaea lycioides (Rusby) Sandwith(Rubiaceae), including three derivatives that have not been described before: a hetero-bianthraquinoneidentified as (R)-2-hydroxymethyl-20methyl-1,10,6,60-tetrahydroxy-5,50 bianthraquinone (lycionine), andtwo mono-chlorinated derivatives related to soranjidiol. One of them is a homo-bianthraquinone: (R)-7-chloro-2,20-dimethyl-1,10,6,60-tetrahydroxy-5,50 bianthraquinone (7-chlorobisoranjidiol), whereas thesecond halogenated derivative corresponds to a monomeric structure: 5-chloro-1,6-dihydroxy-2-methylanthraquinone (5-chlorosoranjidiol). The four known compounds were already isolated from anotherspecies of this genus, H. pustulata, and they were identified as 5,50-bisoranjidiol, soranjidiol, pustulineand heterophylline. Structural elucidation was performed by means of an extensive spectroscopicanalysis, including 1D and 2D NMR data as well as by HRMS analysis. Chemical structures of 7-chlorobisoranjidiol and 5-chlorosoranjidiol were confirmed by their synthesis from 5,50-bisoranjidioland soranjidiol, respectively. Type I photosensitizing properties (superoxide anion radical generation,O2) were assessed by using the nitroblue tetrazolium assay. When lycionine and chlorinated derivativeswere irradiated, they enhanced the O2 production with respect to the control; 7-chlorobisoranjidiolstood out by generating an increase of 20%, whereas the other anthraquinones only produced a slightincrease of 7%.