Isolation, characterization and antimicrobial analysis of Ethyl gallate and Pyrogallol from Acalypha wilkesiana var. lace-acalypha (Muell & Arg.)

Abstract

Background: Acalypha wilkesiana var. lace-acalypha (Muell & Arg.) is a cultivated ornamental plant used in folkloric medicine for the treatment of fever, bacterial, skin fungal infections, wounds, tumors, inflammations and gastro-intestinal troubles. To date, there are no reports of any isolated compounds from this species/variety which could serve as chemotaxonomic markers. Hence, the need for this study.

Objectives: The leaves of the plant were to be collected and extracted cold in 50 % ethanol to obtain the crude extract. The aqueous solution of the crude extract was to be  partitioned with butanol. The obtained butanol fraction was to be separated on a silca-gel column to obtain isolates which were to be screened for antimicrobial activities.

Methodology: Isolates expected to be obtained from the silica-gel column chromatography of the butanol fraction were to be analyzed for antimicrobial activities using the hole-in agar diffussion method. The compounds were to be screened for both antibacterial and antifungal activities using the microbes namely, B. subtilis, S. aureus, E. coli, Ps. aeriginosa and S. typhi. and C. albicans.

Results and Discussion: Two polyphenolic compounds, designated as compounds 1 [m.pt (148-150 ⁰C); R_f (0.67); [n]²⁰_D (1.4118 )] and 2 [(m.pt 130-132 ⁰C); R_f (0.46); [n]²⁰_D (1.4079)] were isolated. The structures of 1 and 2 have been established to be ethyl 3, 4, 5-trihydroxybenzoate (ethyl gallate) and 1, 2, 3-benzenetriol (pyrogallol or fouramine brown) respectively using the ¹H NMR, ¹³C NMR, MS and IR spectral techniques. Both polyphenols were strongly bacteriostatic against B. subtilis, S. aureus, E. coli, Ps. aeriginosa and S. typhi. Furthermore, 2 was more suppressive of the bacterial strains than 1. However, neither gave any anticandidal activity. The crude extract and butanol fraction demonstrated comparatively weaker antimicrobial activities than the two isolated compounds.

Conclusion: The two polyphenols would serve as chemotaxonomic markers for this species/variety and the genus, Acalypha in general. Also the results of the antimicrobial screening have lent scientific credence to the traditional uses of the plant.

Key words: Polyphenols; ethyl gallate; pyrogallol; bacteriostatic; A. wilkesiana var. lace-acalypha