Identification, isolation, and characterisation of bioactive compounds from Hypoestes aristata (Acanthaceae) and Leucosidea sericea (Rosaceae)

Abstract

The aim of this study was to identify and isolate potential biologically active compounds from the leaves and stems of Hypoestes aristata (Vahl) Sol. ex Roem. & Schult (Acanthaceae) and Leucosidea sericea Eckl. & Zeyh. (Rosaceae) and test them for their biological activities. The identification and isolation of potential bioactive compounds was achieved through chromatographic techniques such as column chromatography, preparative thin layer chromatography (PTLC), preparative high pressure liquid chromatography (Prep-HPLC), liquid chromatography-solid phase extraction-mass spectrometry (LC-SPE-MS), and ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UHPLC-qTOF-MS). The characterisation and structural elucidation of the isolated compounds was mainly facilitated by spectroscopic/spectrometric techniques including 1D NMR (1HNMR, 13C-NMR, dept-135) and 2D NMR (COSY, HSQC, HMBC, NOESY) and high-resolution mass spectrometry (HRMS).

From the Hypoestes arisata plant study, ten compounds that belong to the class of lignans were isolated and characterised. Among these compounds, four known butyrolactone lignans hinokinin, savinin, and cubebins; three new butyrolactone lignans (7S,8S,7'S,8'R)-7'-acetoxy-7-hydroxyhinokinin, (7S,8S,7'S,8'R)-7-acetoxy-7'-hydroxyhinokinin, and (7S,8S,7'S,8'R)-7,7'-diacetoxyhinokinin; and three new butyrolactol lignans (7R,8S,9R,7′R,8′R)-7,7′-diacetoxycubebin, 7,7'-diacetoxy-β-cubebin, and (7S,8R,9S,7'R,8'R)-7,7'-diacetoxycubebin) were isolated. The absolute configurations of novel compounds were determined from their electronic circular dichroism (ECD) spectra and by derivatisation into (S) and (R)-MTPA esters. The newly isolated compounds are novel compounds. To the best of our knowledge, this is the first research which has isolated these compounds and confirm their absolute configurations from H. aristata.

Hinokinin, (7S,8S,7'S,8'R)-7'-acetoxy-7-hydroxyhinokinin, (7S,8S,7'S,8'R)-7,7'-diacetoxyhinokinin, and (7R,8S,9R,7′R,8′R)-7,7′-diacetoxycubebin were tested for inhibition of HIV-1 protease enzyme. Other compounds were not tested due to insufficient quantities for biological activity studies. The results indicated that hinokinin and (7S,8S,7'S,8'R)-7,7'-diacetoxyhinokinin showed moderate protease inhibition at concentrations below 60 µM and other two compounds showed significant inhibitory activities at concentrations above 100 µM. Additionally, the compounds (7S,8S,7'S,8'R)-7'-acetoxy-7-hydroxyhinokinin, (7S,8S,7'S,8'R)-7,7'-diacetoxyhinokinin, and (7R,8S,9R,7′R,8′R)-7,7′-diacetoxycubebin were also tested for cytotoxicity against the MCF-7 and MDA-MB-231 cancer cell lines and found to be inactive at concentrations below 90 µM.

From the Leucosidea sericea plant, a detailed phytochemical profiling study led to the identification of fourty compounds, which include twenty-three flavonoids and chromones, ten phloroglucinols and seven terpenoids. In L. sericea, eleven of these compounds have previously been identified and isolated. To the best of our knowledge twenty-nine of these compounds were identified for the first time in L. sericea. Furthermore, this is the first detailed phytochemical study of this plant.

Additionally, twenty compounds were isolated and characterised. These included a phloroglucinol derivative, phlorisovalerophenone; three chromones 5,7-dihydroxychromone, eugenin, and 5-hydroxychromone-7-O-β-glucopyranoside; eight flavonoids apigenin, kaempferol-3-O-β-glycopyranoside, quercetin-3-O-β-glucopyranoside, quercetin-3-O-β-galactopyranoside, quercetin-3-O-α-arabinopyranoside, kaempferol-3-O-α-arabinopyranoside, kaempferol-3-O-rutinoside, and kaempferol-3-O-β-(6″-p-coumaroyl)-glucopyranoside; and eight triterpenoids 1-hydroxy-2-oxopomolic acid, 2-oxopomolic acid, 3-oxopomolic acid, ursolic acid, corosolic acid, tormentic acid, pomolic acid, and β-sitosterol glucoside. Sixteen of these compounds were isolated for the first time from this plant. Biological activity studies of these compounds have been done before. Isolation of more material is required to conduct further biological activity studies of the compounds