Chemical constituents from Macaranga hypoleuca (Rchb.f. & Zoll.) Müll.Arg. and their radical scavenging activity

Abstract

Euphorbiaceae is the fourth most prominent angiosperm family, with over 300 genera and 8,000 species, the largest of which is Macaranga. The leaves have traditionally been used to treat swelling, new cuts, ulcers, bruises, and boils. This genus is also vital for honeybee propolis production in Okinawa, Japan, and Taiwan. Macaranga contains a high concentration of flavonoids and stilbenoids, both of which exhibit a broad range of bioactivities. Due to that, Macaranga hypoleuca was selected for phytochemical and biological research. This study aimed to isolate chemical compounds from the stems and leaves of the species using various chromatographic methods and determine their isolated compounds' structure using several spectroscopic techniques. The powdered leaves of M. hypoleuca (2.5 kg) were macerated in methanol at room temperature for 24 hrs and repeated thrice. The crude extract of leaves obtained (700 g) was partitioned with nhexane and ethyl acetate. Vacuum liquid chromatography (VLC) was used to fractionate the crude ethyl acetate (370 g) into eight fractions (HL1-8). Fraction HL5 (2.3 g) was subjected to VLC, column chromatography (CC) and preparative thin layer chromatography (p-TLC) to give a pure compound (1) (5.8 mg). Fraction HL6 (10.6 g) was fractionated using VLC twice, followed by purification using CC, high-performance liquid chromatography (HPLC) and p-TLC to afford pure compounds (2) (26.4 mg), (3) (6.0 mg) and (4) (2.0 mg). Another pure compound (5) (6.0 mg) was obtained from the crude acetone extract of the stem bark through fractionation, isolation and purification processes. The pure compounds were characterised based on the NMR, MS, UV-Vis and IR analyses as well as a comparison to published data. Three flavonoids known as tomentosanol D (1), quercetin (2) and kaempferol (3) as well as a phenolic acid namely 3,4-dihydroxybenzoic acid (4) were isolated from the leaves whilst a coumarin, scopoletin (5) was obtained from the stem bark of M. hypoleuca. Compounds 2 – 3 exhibited good activity on DPPH radical scavenging with the percent inhibition values of 93.85% and 93.81%, respectively.