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Enzyme inhibitors play a significant role in the drug discovery process. For instance, acetylcholinesterase (AChE) inhibitors have applications in curing Alzheimer’s disease (AD), senile dementia, ataxia, myasthenia gravis, and Parkinson’s disease. Glutathione S-transferase (GST) inhibitors have applications as adjuvants to overcome anticancer and antiparasitic drug resistance problems. Compounds inhibiting the activity of α-glucosidase are used to treat type 2 diabetes mellitus and obesity problems. This article describes the identification of natural products exhibiting AChE, GST, and α-glucosidase inhibitory activities from medicinally important plants. Additionally, structure–activity relationship (SAR) studies of these newly discovered enzyme inhibitors are also discussed.

Naturally occurring enzyme inhibitors play an important role in a drug discovery program. Glutathione S-transferases (GSTs) play a significant role in the detoxification and metabolism of many xenobiotic and endobiotic compounds. GSTs are considered to be responsible for decreasing the effectiveness of anticancer/antiparasitic agents used for the treatment of cancer and parasitic diseases. The effectiveness of these biomedical agents may be improved by using GST inhibitors as an adjuvant during chemotherapy. Acetylcholinesterase (AChE) inhibitors have potential applications in curing cardiac problems and Alzheimer's disease. This article describes the identification of natural products exhibiting GST and AChE inhibitory activities, from medicinally important plants. Results obtained from the structure-activity relationship (SAR) studies of some of these newly discovered enzyme inhibitors are also discussed.

Phytochemical studies on the methanolic extract of the leaves of Buxus hyrcana pojark, collected in Iran, have resulted in the isolation of two new triterpenoidal alkaloids, (+)-2α,16β ,31- triacetylbuxiran (1), (+)-2α,16β ,31-triacetyl-9-11-dihydrobuxiran (2). Spectroscopic methods were used to elucidate the structures of these new natural products.

Fungal biotransformations of alpha-santonin (1) were conducted with Mucor plumbeus (ATCC 4740), Cunninghamella bainieri (ATCC 9244), Cunninghamella echinulata (ATCC 9245), Curvularia lunata (ATCC 12017) and Rhizopus stolonifer (ATCC 10404). Rhizopus stolonifer (ATCC 10404) metabolized compound 1 to afford 3,4-epoxy-alpha-santonin (2) and 4,5-dihydro-alpha-santonin (3) while Cunninghamella bainieri (ATCC 9244), Cunninghamella echinulata (ATCC 9245) and Mucor plumbeus (ATCC 4740) were capable of metabolizing compound 1 to give a reported metabolite, 1,2-dihydro-alpha-santonin (4). The structures of these transformed metabolites were established with the aid of extensive spectroscopic studies. These fungi regiospecifically reduced the carbon-carbon double bond in ring A of alpha-santonin.

Phytochemical studies on the ethanolic extract of the roots of Buxus sempervirens of Turkish origin have resulted in the isolation of two new triterpenoidal alkaloids, (+)-16α, 31- diacetylbuxadine (1), (-)-Nb-demethylcyclomikuranine (2) along with three known natural products, (-)-cyclomikuranine (3), (-)-cyclobuxophylline-K (4) and (+)-buxaquamarine (5) isolated for the first time from this species of genus Buxus. The structures of these new natural products were established on the basis of extensive spectroscopic studies. Compound 1 exhibited antibacterial activity against human pathogenic bacteria and weak phytotoxic activity against Lemna minor Linn.