Theoretical Inquiry, Bioactive Characterization of Stigmasterol / βSitosterol from the Bulbs of Calotropis procera ('Sodom apple')

Abstract

This work characterizes sigmasterol from Calotropis procera bulbs and investigates the antimicrobial activities of the crude. The air dried pounded and sieved bulbs were extracted with 500 mL each of n-hexane, ethyl acetate and methanol respectively. Screening of the crude, extracted in the above solvents revealed the presence of alkaloids, flavanoids, reducing sugars, saponins, steroids, and tannis.  Anthraquinones were below detection level. Microbial bioassay was carried out against Nectricillin resistant Staphylococcus aureus, Vancomycin resistant Enterococci, Escherichia coli, Profeus mirabilis, Salmonella typhi, Pseudomonas aeruginosa, Candida albicans, Neisseria gonorrhea, Candida krusei and Candida stellafoidea. Ethyl acetate extract had the highest effective activity against Escherichia coli (MIC 2.5mg/mL and MBC/MFC 5mg/mL), Staphylococcus aureus (MIC 2.5mg/mL), Candida albicans, Salmonella typhi and Candida stellafoidea (MIC 5mg/mL). Extracts were subjected to column and thin layer chromatographic purification. The purified fractions were found to be white crystalline solids.  Structures of the bioactive fractions were thoroughly elucidated using NMR spectroscopy, and comparison of their chemical shifts with literature confirmed the presence of the Stigmasterol and β-Sitosterol. Further studies revealed that the compounds possess profound anti-malarial, anti-ulcer, anti-tumour, antifungal, antibacterial, analgesic and other pharmacological properties. Thus, this strong activity of the crude extracts against Escherichia coli and Salmonella typhi indicated that these molecules have anti-diarrheal activity. Molecular docking studies on the binding interaction between the DNA gyrase of Escherichia coli and Salmonella typhi revealed that the compounds majorly bind with the active sites of the target protease via hydrophobic and hydrogen bond interactions with binding activity of -7.8 kcal/mol, equivalent to the standard. In silico Drug-likeness and ADMET investigations of the compounds revealed their sound oral bioavailability, excellent pharmacokinetic and toxicity profiles. Thus, the bulbs of the P. procera are pharmacokinetically effective and efficient on above microorganisms and obey both the Lipinski and the Veber rules.