Metabolic fingerprinting, antioxidant characterization, and enzyme-inhibitory response of Monotheca buxifolia (Falc.) A. DC. extracts
Authors: Ali Joham Sarfraz , Saleem Hammad , Mannan Abdul , Zengin Gokhan , Mahomoodally Mohamad Fawzi , Locatelli Marcello , Abidin Syafiq Asnawi Zainal , Ahemad Nafees , Zia Muhammad 
Published: October 2020

Abstract
Background
Ethnobotanical and plant-based products allow for the isolation of active constituents against a number of maladies. Monotheca buxifolia is used by local communities due to its digestive and laxative properties, as well as its ability to cure liver, kidney, and urinary diseases. There is a need to explore the biological activities and chemical constituents of this medicinal plant.

Methods
In this work, the biochemical potential of M. buxifolia (Falc.) A. DC was explored and linked with its biological activities. Methanol and chloroform extracts from leaves and stems were investigated for total phenolic and flavonoid contents. Ultrahigh-performance liquid chromatography coupled with mass spectrometry (UHPLC–MS) was used to determine secondary-metabolite composition, while high-performance liquid chromatography coupled with photodiode array detection (HPLC–PDA) was used for polyphenolic quantification. In addition, we carried out in vitro assays to determine antioxidant potential and the enzyme-inhibitory response of M. buxifolia extracts.

Results
Phenolics (91 mg gallic-acid equivalent (GAE)/g) and flavonoids (48.86 mg quercetin equivalent (QE)/g) exhibited their highest concentration in the methanol extract of stems and the chloroform extract of leaves, respectively. UHPLC–MS analysis identified a number of important phytochemicals, belonging to the flavonoid, phenolic, alkaloid, and terpenoid classes of secondary metabolites. The methanol extract of leaves contained a diosgenin derivative and polygalacin D, while kaempferol and robinin were most abundant in the chloroform extract. The methanol extract of stems contained a greater peak area for diosgenin and kaempferol, whereas this was true for lucidumol A and 3-O-cis-coumaroyl maslinic acid in the chloroform extract. Rutin, epicatechin, and catechin were the main phenolics identified by HPLC–PDA analysis. The methanol extract of stems exhibited significant 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS) radical-scavenging activities (145.18 and 279.04 mmol Trolox equivalent (TE)/g, respectively). The maximum cupric reducing antioxidant capacity (CUPRAC) (361.4 mg TE/g), ferric-reducing antioxidant power (FRAP) (247.19 mg TE/g), and total antioxidant potential (2.75 mmol TE/g) were depicted by the methanol extract of stems. The methanol extract of leaves exhibited stronger inhibition against acetylcholinesterase (AChE) and glucosidase, while the chloroform extract of stems was most active against butyrylcholinesterase (BChE) (4.27 mg galantamine equivalent (GALAE)/g). Similarly, the highest tyrosinase (140 mg kojic-acid equivalent (KAE)/g) and amylase (0.67 mmol acarbose equivalent (ACAE)/g) inhibition was observed for the methanol extract of stems.

Conclusions
UHPLC–MS analysis and HPLC–PDA quantification identified a number of bioactive secondary metabolites of M. buxifolia, which may be responsible for its antioxidant potential and enzyme-inhibitory response. M. buxifolia can be further explored for the isolation of its active components to be used as a drug.