Shahid Malik

Studies on the chemical constituents of Phyllanthus emblica

Phytochemical investigations on Phyllanthus emblica have resulted in the isolation of the two new flavonoids, kaempferol-3-O-α-L-(6″-methyl)-rhamnopyranoside (1) and kaempferol-3-O-α-L-(6″-ethyl)-rhamnopyranoside (2). Their structures were determined on the basis of extensive spectroscopic studies including 2D-NMR experiments.

New isoflavones from Ceiba pentandra

Two new isoflavones, pentandrin (1) and pentandrin glucoside (2), were isolated from the stem barks of Ceiba pentandra along with beta-sitosterol and its 3-O-beta-D-glucopyranoside, which was isolated for the first time from this plant. The structures of these compounds were elucidated with the help of spectroscopic techniques, while the structure of 1 was unambiguously confirmed by single-crystal X-ray diffraction studies.

Spatozoate and varninasterol from the brown alga Spatoglossum variabile

Two new compounds, spatozoate and varninasterol were isolated from Spatoglossum variabile. Four known compounds, fucosterol, cholesta-5-ene-23-yne-3β-ol, apiole and nothoapiole were also isolated for the first time from the methanolic extracts of this alga. The structure elucidation of the new compounds were carried out with the help of modern spectroscopic techniques.

Two saponins from Pteleopsis hylodendron

Abstract Two new saponins, 2α,3α,19α,23-tetrahydroxyolean-12-en-28-O-β- d -galactoside, and sitosterol α(1→3) diglucoside, were isolated from the stem barks of Pteleopsis hylodendron along with a known triterpenoid, 2α,3β,21β,23-tetrahydroxyolean-12-en-28-oic acid, which was isolated for the first time from this plant. The structures of these compounds were elucidated with the help of spectroscopic studies.

Triterpenes from Mimusops elengi

Abstract Pentacyclic triterpenes (1) and (2) have been isolated from Mimusops elengi and assigned structures 3β,6β,19α,23-tetrahydroxy-urs-12-ene and 1β-hydroxy-3β-hexanoyllup-20 (29)-ene-23, 28-dioic acid, respectively, on the basis of spectroscopic studies including 2D-NMR. The compound 1 showed moderate inhibiting activity against β-glucuronidase enzyme

Chirality Recognition of Selenium Compounds by NMR Spectroscopy in the Presence of a Chiral Dirhodium Complex

Abstract Diastereomeric adducts of chiral soft-base selenium ligands with the enantiopure dirhodium complex Rh* allows stereodifferentiation by NMR spectroscopy of various nuclei (dirhodium method). The individual adduct species can be identified by low-temperature NMR spectroscopy.

Chemical Composition and Antitumor Activities from Givotia madagascariensis

Abstract Two new erythroxylane diterpenes, named givotin A (1) and givotin B (2) were isolated from the bark of Givotia madagascariensis. Their structures have been established as 3α,12α-dihydroxy- 4(19),15-erythroxyladiene (1) and 3α-hydroxy-4(19),15-erythroxyladiene (2), respectively, on the basis of one and two-dimensional NMR spectroscopic studies (1H, 13C, COSY, HMQC, HMBC, NOESY, NOE difference spectra) as well as on mass spectral analysis. In addition six known compounds (3 - 8) have been isolated and identified. Cleistanthol (3), spruceanol (4) and 1,2- dihydroheudelotinol (5) demonstrated significant antitumor activities against three tumor cell lines (HM02, Hep G2, MCF7).

Chemical Constituents From Marine Organisms

Abstract Two new compounds, spatosterol (1) and thyminol (2) were isolated from Spatoglossum variabile and colonial Zoanthid, respectively. Three known compounds, 2-deoxyinosine (3), 2-deoxythymidine (4) and hexadecylhexadecanoate (5) were also isolated for the first time from the methanolic extract of the colonial Zoanthid.

Dirhodium tetraacylate complexes and monovalent ligands. Adduct formation in solution as monitored by NMR spectroscopy

Evidences of adduct formation between the dirhodium complex Rh2[(R)-MTPA4] (Rh–Rh; MTPA-H = Mosher acid) and various monovalent ligands L were obtained in solution by using NMR spectroscopy. Strongly binding ligands, e.g. selenoethers or nitriles, prefer L → Rh–Rh ← L adducts whereas weaker ligands, e.g. olefins with low steric hindrance, tend to form oligomers with bridging L molecules: ⋯Rh–Rh⋯L⋯Rh–Rh⋯. Larger steric congestion forces olefins to avoid bridge situations or even prohibits adduct formation at all.