Leishmanicidal and antimicrobial activity of primin and primin-containing extracts from Miconia willdenowii.

As a part of an ongoing bioprospective project, searching for potential medicinal plants from the Brazilian Atlantic Forest, Miconia willdenowii was selected for its potential leishmanicidal and antimicrobial activities. The crude ethanolic extract of M. willdenowii showed an inhibition of 99.7% of the promastigote forms of Leishmania amazonensis at the concentration of 80 μg/mL. Further investigation of its antimicrobial activity against pathogenic fungi and Gram positive and negative bacteria, revealed a significant antimicrobial activity. A bioguided study with its liquid-liquid partition fractions revealed the hexane fraction (Hex) as the most active against Leishmania, inhibiting 99.2% and 46.9% of the protozoan at concentrations of 40 and 20 μg/mL, respectively. Hex also showed significant antimicrobial activity against Staphylococcus aureus and Candida krusei with IC₅₀ of 15.6 and 62.5 μg/mL, respectively. Purification of Hex led to the isolation of 2-methoxy-6-pentyl-benzoquinone (1, also known as primin) as the active metabolite, probably responsible for the observed antimicrobial and anti-leishmania effects. Primin (1) disclosed leishmanicidal activity (IC₅₀ = 1.25 μM), showing higher potency than the standard drug amphotericin B (IC₅₀ = 5.08 μM), with additional antifungal effects against all tested fungi species. Compound 1 also showed significant activity against S. aureus (IC₅₀ = 8.94 μM), showing a comparable potency with the reference drug chloramphenicol (IC₅₀ = 6.19 μM), but with a potential cytotoxicity towards peripheral human blood mononuclear cells (CC₅₀ = 255.15 μM). Here in, the antimicrobial and anti-L. amazonensis effects of M. willdenowii are reported for the first time, as well as Primin (1) as its probable bioactive metabolite.