Methods
Plant material and preparation of extracts
Fresh leaves of plants as listed in Table 1 were collected from Darjeeling district of West Bengal, India. The specimens were identified and the voucher specimens were assigned specific reference number (Table 1).The leaves were washed thoroughly, air-dried and crushed. The crushed samples were extracted with 95% ethanol (1 g in 10 ml ethanol) for 72 h at 37°C with occasional shaking. After 72 h, the extract was filtered through a Whatman no. 1 filter paper and the filtrate was evaporated to dryness using a rotary evaporator (RV 10 Digital, IKA, Germany). The dried samples were stored at −20°C until use.