The Need for Establishing Identities of 'Bacoside A and B', the Putative Major Bioactive Saponins of Indian Medicinal Plant Bacopa Monnieri (Short Communication‪)‬

Bacopa monnieri (Linn.) Pennel (Scrophulariaceae), commonly known as brahmi, is an important drug in Ayurveda for improvement of intelligence, memory and revitalisation of sensory organs (Sivarajan and Balachandran, 1994). The nootropic activity of the plant has been well studied by several researchers and alcoholic/hydroalcoholic extracts of the whole plant have been proved to possess the activity (Singh and Dhawan, 1982; Prakash and Sirsi, 1962 and Table 1). The major chemical constituents isolated and characterized (by spectral techniques) from the alcoholic extract are dammarane type of triterpenoid saponins with jujubogenin (1) and pseudojujubogenin (2) as aglycones. These include bacosides [A.sub.1]-[A.sub.3], bacopasaponins A-G, bacopasides I-III (Table 2) and bacopasides III-V (Chakravarty et al. 2003). However, the nootropic activity of the extract has been attributed to the presence of two major saponins named as 'bacoside A and B' (Singh et al. 1988; Dhawan and Singh, 1996; Singh and Dhawan, 1997). The structure of 'bacoside A' was initially deduced as 3-([alpha]-L-arabinopyranosyl)-O-[beta]-D-glucopyranosid-10,20-dihydroxy-16-keto-dammarene-(24) (3) mainly by analyzing the acid hydrolysis products of 'bacoside A' (Chatterji et al. 1965). Five acid hydrolysis products were subsequently identified as bacogenins [A.sub.1]-[A.sub.5] (Chandel et al. 1977; Rastogi et al. 1993), among which the major component was ebelin lactone (bacogenin [A.sub.4]), the acid hydrolysis product derived from jujubogenin. 'Bacoside B' was found to be identical to 'bacoside A' in respect of their carbohydrate and the aglycone moieties as determined by iodometry, gravimetry, colorimetry and analysis of acid hydrolysis products (Basu et al. 1967). In addition, 'bacoside B' was found dextro-rotatory and 'bacoside A' levo-rotatory, which was explained as due to the 'differences in configuration of carbohydrate chain' in the two saponins. However, in the subsequent studies (Kawai and Shibata, 1978) it became known that 'bacoside A' was a mixture of saponins and was not a single chemical entity as 'bacoside A' was resolved into two fractions (which again were mixtures) by droplet counter-current extraction. Also two genuine sapogenins of 'bacoside A' viz. 1 and 2 were isolated and characterized. No further literature reports seem to be available on the structure/composition of 'bacoside A and B'. Hence there exists a confusion on chemical identities of 'bacoside A and B.' On the other hand, several pharmacological and clinical studies on the extracts of B. monnieri 'standardized' to the content of 'bacoside A and B' are being published (Table 1). Many products derived from B. monnieri are available in the international nutraceutical market with label claims on the content of 'Bacoside A and B'. Estimation procedures for 'bacoside A' by HPTLC (Gupta et al. 1998) and UV (Pal and Sarin, 1992) are available. 'Bacoside A and B' themselves have been studied for biological activities (Singh et al. 1988; Giri and Khan 1996; Chowdhuri et al. 2002; Dhawan and Singh, 1996). Besides, several agronomy related studies on 'bacoside A' content in B. monnieri have been published (Ganjewala et al. 2001; Gupta et al. 1998; Mathur et al. 2001). Production of 'bacoside A' by cell suspension cultures has been tried (Rahman et al. 2002).