title: Bioassay-guided fractionation and identification of α-amylase inhibitors from Syzygium cumini leaves.
abstract: BACKGROUND
  Pancreatic α-amylase and α-glucosidase inhibitors serve as important strategies in the management of blood glucose. Even though Syzygium cumini (L.) Skeels (Myrtaceae) (SC) is used extensively to treat diabetes; scientific evidence on antidiabetic effects of SC leaves is scarce.
  
  
  OBJECTIVE
  SC leaf extract was investigated for α-amylase inhibitory effect and continued with isolation and identification of α-amylase inhibitors.
  
  
  METHODS
  Bioassay-guided fractionation was conducted using in vitro α-amylase inhibitory assay (with 20-1000 μg/mL test material) to isolate the inhibitory compounds from ethyl acetate extract of SC leaves. Structures of the isolated inhibitory compounds were elucidated using1H NMR and13C NMR spectroscopic analysis and direct TLC and HPLC comparison with authentic samples. Study period was from October 2013 to October 2015.
  
  
  RESULTS
  An active fraction obtained with chromatographic separation of the extract inhibited porcine pancreatic α-amylase with an IC50of 39.9 μg/mL. Furthermore, it showed a strong inhibition on α-glucosidase with an IC50of 28.2 μg/mL. The active fraction was determined to be a 3:1 mixture of ursolic acid and oleanolic acid. Pure ursolic acid and oleanolic acid showed IC50values of 6.7 and 57.4 μg/mL, respectively, against α-amylase and 3.1 and 44.1 μg/mL respectively, against α-glucosidase.
  
  
  CONCLUSIONS
  The present study revealed strong α-amylase and α-glucosidase inhibitory effects of ursolic acid and oleanolic acid isolated from SC leaves for the first time validating the use of SC leaves in antidiabetic therapy.
authors.affiliation: a Postgraduate Institute of Science, University of Peradeniya , Peradeniya , Sri Lanka.
authors.forename: Jeyakumaran
authors.initials: J
authors.lastname: Poongunran
authors.affiliation: b Department of Biochemistry, Faculty of Medicine , University of Peradeniya , Peradeniya, Sri Lanka.
authors.forename: Handunge Kumudu Irani
authors.initials: HK
authors.lastname: Perera
authors.affiliation: c Institute of Fundamental Studies , Kandy , Sri Lanka.
authors.forename: Lalith
authors.initials: L
authors.lastname: Jayasinghe
authors.affiliation: b Department of Biochemistry, Faculty of Medicine , University of Peradeniya , Peradeniya, Sri Lanka.
authors.forename: Irushika Thushari
authors.initials: IT
authors.lastname: Fernando
authors.affiliation: b Department of Biochemistry, Faculty of Medicine , University of Peradeniya , Peradeniya, Sri Lanka.
authors.forename: Ramaiah
authors.initials: R
authors.lastname: Sivakanesan
authors.affiliation: d School of Agriculture , Meiji University , Tama-ku , Kanagawa , Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Araya
authors.affiliation: c Institute of Fundamental Studies , Kandy , Sri Lanka.|d School of Agriculture , Meiji University , Tama-ku , Kanagawa , Japan.
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Fujimoto
mesh_terms: D000085:Acetates / Q000737:chemistry; D001681:Biological Assay; D066241:Carbon-13 Magnetic Resonance Spectroscopy; D002851:Chromatography, High Pressure Liquid; D002855:Chromatography, Thin Layer; D065089:Glycoside Hydrolase Inhibitors / Q000302:isolation & purification / Q000494:pharmacology*; D007004:Hypoglycemic Agents / Q000302:isolation & purification / Q000494:pharmacology*; D015394:Molecular Structure; D009828:Oleanolic Acid / Q000302:isolation & purification / Q000494:pharmacology; D010179:Pancreas / Q000187:drug effects* / Q000201:enzymology; D010936:Plant Extracts / Q000302:isolation & purification / Q000494:pharmacology*; D018515:Plant Leaves / Q000737:chemistry*; D066244:Proton Magnetic Resonance Spectroscopy; D012997:Solvents / Q000737:chemistry; D027842:Syzygium / Q000737:chemistry*; D014315:Triterpenes / Q000302:isolation & purification / Q000494:pharmacology; D000516:alpha-Amylases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000097245:Ursolic Acid
chemical_list: D000085:Acetates; D065089:Glycoside Hydrolase Inhibitors; D007004:Hypoglycemic Agents; D009828:Oleanolic Acid; D010936:Plant Extracts; D012997:Solvents; D014315:Triterpenes; D000516:alpha-Amylases; D000097245:Ursolic Acid; C007650:ethyl acetate
keywords: oleanolic acid; ursolic acid; α-Glucosidase