Ruchi G. Marwah

Antimicrobial activity and the major components of the essential oil of Plectranthus cylindraceus

Aims:  The traditional uses of the aerial parts of fresh Plectranthus cylindraceus by the Dhofaris in Oman were investigated on the basis of antimicrobial properties and composition of its herb oil.

Identification of the chemotypes of Ocimum forskolei and Ocimum basilicum by NMR spectroscopy

The chemotypes of Ocimum forskolei Benth and Ocimum basilicum L. growing wild in Oman have been established by 13C‐NMR analyses of the vegetative and floral oils of the plants. The chemotypes, estragole for O. forskolei and linalool for O. basilicum, suggested by 13C‐NMR fingerprinting were also confirmed by GC‐FID and GC/MS analyses. The oil of O. forskolei demonstrated better activities against bacteria and dermatophytes. The significance of the presence of estragole and linalool in the volatile oils of plants whose fragrances are traditionally inhaled, added to food, or rubbed on the skin are discussed.

13C NMR Analysis and Antifungal and Insecticidal Activities of Oman Dill Herb Oil

Abstract The major chemical components of Oman dill herb oil (oil from the leaves and flowering tops of Anethum graveolens. L. grown in Oman) were analyzed by 13C NMR spectroscopy. The activities of oil against bacteria, fungi, and aphids were also evaluated. The oil was inactive against Gram-positive and Gram-negative bacteria at low concentrations. It inhibited the growth of Candida albicans. and some molds that cause crop or food damage but demonstrated weak contact toxicity to aphids. The most abundant oil components were identified as limonene and dillapiole by 13C NMR analysis. Carvone, the spicy and antibacterial component of European dill oil, was absent.

ent-kaurene diterpenoids from Blepharispermum hirtum

The twigs and leaves of Blepharispermum hirtum Oliver (Asteraceae) were investigated for their larvicidal and antimicrobial activity. Fractionation of the extracts of the twigs, directed by brine shrimp test and antibacterial activities, led to the isolation of compounds 1–4; two of which are new ent‐kaurene diterpenoids, blepharispins A and B (1 and 2, resp.). The structures of compounds 1 and 2 were established from spectral data. The absolute configuration at C(15) in 1 was inferred from Mosher ester analysis and relative configurations were suggested by a NOESY experiment. Compound 4 was significantly larvicidal to newly hatched naupleii of Artemia salina L. (BST LC50=1.3 (3.7–0.0) μg/ml), but the blepharispins were not (BST LC50>500 μg/ml). Nevertheless, compound 1 inhibited the growth of Staphylococcus aureus and Bacillus subtilis at a MIC value of 62.5 μg/ml. The significance of the bioactivity results and the presence of ent‐kaurene diterpenoids in B. hirtum are discussed from biosynthetic and local utilization viewpoints.