No abstract

Four diketopiperazine derivatives; cyclo(-Pro-Val) (1), (-)-cyclo(-Pro-Tyr) (2), (-)-cyclo(-Pro-Phe) (3) and (+)-cyclo(-Pro-Leu) (4) were isolated from the ethyl acetate extract of Glaciozyma antarctica PI12, a cold-adapted yeast that belongs to family Kriegeriales. The compounds were isolated by radial chromatography and thin layer chromatography techniques and the chemical structures were elucidated by infrared (IR), ultraviolet (UV), nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry.

Polygonumins B, C and D, derivative compounds of polygonumins A, were isolated from the stem of Polygonum minus. Based on NMR results, the structure of polygonumins derivatives is comprised of four phenylpropanoid units and a sucrose unit, with a similar structure to polygonumins A. However, the structural differences between polygonumins B (1), C (2) and D (3) can be distinguished based on the existence of methoxy, ethanoyl and hydroxyl groups and protons which bind to C-4, C-4′ and C-3″. Interestingly, these bioactive compounds showed various medicinal properties based on our investigation on antioxidant, anticholinesterase and anti-HIV-1 protease activities. The IC50 value of DPPH and ABTS (antioxidant activities) was in the following descending order: polygonumins B > polygonumins C > polygonumins A > polygonumins D. In addition, almost similar pattern of antioxidant activity was observed for anti-acetylcholinesterase activity based on its IC50 value in descending order: polygonumins B > polygonumins C > polygonumins D > polygonumins A. On the other hand, polygonumins C and D showed inhibition of HIV-1 protease activity more than the positive control, pepstatin A. Finally, molecular docking studies on AChE and BChE proteins were carried out in order to gain insight into the mode of interactions between these compounds and the active residues for both enzymes. These remarkable findings indicate that these compounds have potential to be developed as targeted drugs for Alzheimer’s disease or as anti-HIV drugs.

A new dipeptide, (-)-glaciantarcin (1) and three known compounds, cyclo(-Pro-Gly) (2), 1-(2-deoxypentofuranosyl)-5methyl-2,4(1H,3H)-pyrimidinedione (3) and vidarabine (Ara-A) (4), were isolated from Glaciozyma antarctica PI12, a cold-adapted yeast. The chemical structures were elucidated by FT-IR, NMR and mass spectrometry. The cytotoxicity and antioxidant activities of compounds 1-4 were evaluated by using the MTT bioassay on MCF-7 (human breast cancer cell line), PC-3 (human prostate cancer cell line) and HEK-293 (normal human embryonic kidney cell line) and DPPH free radical scavenging activity, respectively. At concentration of 400 µM, all compounds showed the highest activity on MCF-7, with compound 1 at 65%, compound 2 (70%), compound 3 (66%) and compound 4 (58%) cell viability. All compounds exhibited weak antioxidant properties. To the best of our knowledge, this is the first report of compounds 1-4 from Glaciozyma antactica.

Meniran (Phyllanthus niruri L.) is a wild plant in the Euphorbiaceae family which grows in tropical climates. The plant is known to possess antioxidant activity and is rich in phenolic compounds. Since plants with high phenolic content and high antioxidant activity are known to exhibit high tyrosinase inhibitory activity, the purpose of this study is to determine the inhibitory activity of the tyrosinase enzyme by the methanol extract of meniran (P. niruri L.) and to isolate secondary metabolites from the extract and fractions which exhibit inhibitory activity against tyrosinase. The in vitro tyrosinase inhibitory activity assay was conducted using the 96-well microplate method with kojic acid as the positive control, while the separation and purification of compounds were carried out using chromatography techniques. The methanol extract and n-hexane fraction showed tyrosinase inhibitory activity with IC50 of 11.05±0.16 and 2.57±0.08 mg/ml, respectively. Three bioactive compounds were succesfully isolated from the n-hexane fraction. Based on the UV and NMR spectra, compounds 1, 2, and 3 were identified as phyllanthin, phyltetralin, and hypophyllanthin, respectively. Furthermore, phyllanthin (1) was shown to demonstrate inhibitory activity against tyrosinase with IC50 of 0.6322 mM. In conclusion, both meniran extract and phyllanthin (1) were found to exhibit inhibitory acitivity against the tyrosinase enzyme. In the future they can be candidates for the treatment against hyperpigmentation and also as an active ingredient in skincare formulations.