Structure and bioactivity studies on the constituents of baphia macrocalyx afzel, baphia keniensis afzel, syzigium cordatum hochst and pavetta teitana k. schum

Phytochemical and biological studies were carried out on four plants from East Africa vis: Baphia macrocalyx Afzel, Baphia keniensis Afzel, Syzigium cordatum Hochst and Pavetta teitana K. Schum. The study aimed at unravelling secondary metabolites of the mentioned plants and carrying out bioactivity studies on the unravelled principles. Phytochemical studies of the leaves of B. Macrocalyx Afzel yielded twelve compounds: ten C-methylated flavones vis: 5- hydroxy-7,4 ́-dimethoxy-6,8-dimethylflavone (112), 5,7-dihydroxy-3,4 ́-dimethoxy-6,8- dimethylflavone (113), 5,7-dihydroxy-4 ́-methoxy-6,8-dimethylflavone (114), 5,4 ́-dihydroxy-7- methoxy-6,8-dimethylflavone (115), 5,4 ́-dihydroxy-3,7-dimethoxy-6,8-dimethylflavone (116), 5,4 ́-dihydroxy-7-methoxy-6-methylflavone (117), 5,4 ́-dihydroxy-3,7-dimethoxy-6- methylflavone (118), 5,7-dihydroxy-3,4 ́-dimethoxy-6-methylflavone (119), 5,7-dihydroxy-4 ́- methoxy-6-methylflavone (120), and 5,7,4 ́-trihydroxy-8-methylflavone (121), together with two other flavones vis: 5,7,4 ́-hydroxy-3 ́-methoxyflavone (122) and 5,7,3 ́,4 ́-tetrahydroxyflavone (123) and one isoflavone, 7-hydroxy-6,4 ́-dimethoxyisoflavone (124). Studies on the dichloromethane/methanol (1:1) extract of the leaves of B. keniensis Afzel yielded the pentacyclic triterpene 3ß-hydroxy-olean-28-oic acid (olenaolic acid) (125) together with two structurally related prenylated flavanones vis 5,7,3 ́,4 ́-tetrahydroxy-2 ́,5 ́-diprenylflavanone (126) and 5,7,3 ́,4 ́-tetrahydroxy-5 ́-prenylflavanone (127). From the methanol extract of the stems of S. cordatum Hochst the pentacyclic triterpenes friedelan-3-one (friedelin) (128) and α- amyrin-3-O-β-D-glucopyranoside (129) together with the phenolic 3-O-methylellagic-α- rhamnopyranose (130) were isolated and identified. Furthermore, the dichloromethane/methanol (1:1) extract of P. teitana K. Schum yielded three pentacyclic triterpenes namely; 3β-hydroxy- urs-12-en-28-oic acid (Ursolinic acid) (131), (3β)-3-Hydroxy-lup-20(29)-en-28-oic acid (betulinic acid) (132) and lup-20(29)-ene-3β,28-diol (Betulin) (133), together with the coumarin 7-hydroxy-6-methoxycoumarin (scopoletin) (134). All the compounds reported here have been isolated for the first time within their respective genera. All of the above compounds are known from literature except for compounds 119 which is new in nature. Compounds 114 and120 are new from nature though their synthesis is reported in literature. Antioxidant tests revealed that compounds with free phenolic hydroxys had the highest activities with 3-O-methylellagic-α- rhamnopyranose (130) having the highest concentration at which the compound inhibited 50% of the DDPH radicals (IC50) value of 13.6 μM. Most compounds tested did not have antimicrobial activity, however, flavonoids with free hydroxy groups in the ring-B gave the highest antimicrobial activity with 5,4 ́-dihydroxy-7-methoxy-6,8-dimethylflavone (115), having the highest antibacterial activity with IC50 value of 1.34 and 0.97 μg/mL against S. aureus and Methicillin Resistant S. aureus (MRS), respectively. In the antileishmanial test, the C-methylated flavone 5,7-dihydroxy-4 ́-methoxy-6-methylflavone (120) had the highest antileishmania activity with IC50 value of 2.7 μg/mL. In this study O-methylation at C-4 of the flavone moiety seemed to enhance anti leishmania activity. Moreover, it was noted that the compounds tested did not show any significant cytotoxic activity against the green monkey kidney fibroblasts (VERO).