Isolation and Characterization of Flavone from the Aerial Parts of Avicennia alba Blume

The present work deals with the isolation and structure elucidation of new flavones from methanol extract of Avicennia alba aerial parts. Isolation of the compound was carried out by chromatographic techniques, followed by different spectral analytical methods. The spectral data of UV-Vis, FT-IR, 1H NMR, 13C NMR and GC-MS of the isolated compound is in support of presence of flavone nucleus. The compound has been characterized as 2-[3'-(3"(hydroxymethyl)oxiran-2"-yl)-2'-methoxy-4'-(methoxymethyl)phenyl]-4H-chromen-4-one.


INTRODUCTION
Plant-based drugs play an important role in both traditional and modern system of medicine 1 .Now a day, plant extracts are used in traditional system of medicine and still continue to provide health coverage over 80% of the world's population in the developing countries 2 .Avicennia alba Blume.(A. alba) is a type of tropical mangrove and classified to the family Avicenniaceae.The plant is distributed in India, Burma, Malacca and Ceylon 3 .The plant is commonly grown in intertidal zones of tropical and sub-tropical area 4 .
It is used for the treatment of several types of diseases such as sexual disorders, scabies, have investigated on the aerial parts of Avicennia alba and reported the isolation and structural elucidation of new the flavone.

Plant materials
The aerial parts of Avicennia alba were collected from Sundarban area, South 24 Parganas, West Bengal, India, in the month of October, 2011 on the basis of Ethnomedicinal uses.The plant was identified & authenticated by the taxonomist from the botanical survey of India, Botanical Garden, Howrah, West Bengal.A voucher specimen (CNH/ 128/2011/TECHII/637) has been deposited in the herbarium of the Department of Pharmacognosy, School of Pharmaceutical Sciences, Siksha O Anusandhan University, Odisha, India.

Extraction and isolation of compound
The air-dried plant materials (500 g) of Avicennia alba were coarsely powdered and extracted in a Soxhlet apparatus with methanol for 48 hours.The methanolic extract was concentrated to obtain a dark viscous mass (64 g).A little amount of the extract was screened chemically for determination of different phytoconstituents.The concentrated extract was dissolved in little quantity of methanol and adsorbed on silica gel (60-120 mesh) for preparation of slurry.The slurry was then air-dried and chromatographed over a silica gel (60-120 mesh) column.The column was eluted with n-hexane initially, then eluted with n-hexane-ethyl acetate mixtures of increasing polarity (95:5, 90:10, 80:20, 70:30, 60:40 and 50:50).Various fractions were collected separately and matched by TLC to check their homogeneity.The fractions with same R f values were combined together and crystallized.The compound was then recrystallized with methanol and finally purified by preparative TLC.The isolated compound was subjected to various physical and spectral studies for characterization.

EXPERIMENTAL
A Soxhlet extractor was used for extraction.The melting point was determined in open capillary tube (Sisco) and is uncorrected.The spectra were recorded with the following instruments, IR: Bruker -FTIR-8400S spectrophotometer using KBr powder; NMR: 1 H NMR and 13 C NMR spectra on Bruker DRX-500 NMR spectrometer using MeOD as the solvent at 500 MHz and 125 MHz respectively; GC-MS: Shimadzu-Mass spectrophotometer; TLC with silica gel GF 254 ; column chromatography silica gel (60-120 mesh, Merck) and elemental analysis: Perkin Elmer-2400 Auto system.