The psychostimulant drug khat (Catha edulis): A mini-review

Khat (Catha edulis Forsk) is a shrub native to the Horn of Africa and the Middle East. The leaves of this small tree are chewed by millions worldwide as a mild, amphetamine-like psychostimulant drug. Whilst khat has enjoyed grey-area legality in many countries including the United Kingdom that otherwise prohibit the use of recreational drugs, recent years have seen the appearance of new legislation to control its production, importation and consumption. This mini-review will consolidate what is known about the pharmacology, chemistry, and effects on health of khat to provide a brief synopsis of the properties of this plant stimulant.     

Antiplasmodial sesquiterpenes from the seeds of Salacia longipes var. camerunensis

Phytochemical investigation of the seeds of Salacia longipes var. camerunensis led to the isolation of four sesquiterpenoid derivatives, salaterpene A (1) (1α,2β,8β-triacetoxy-6β,9β-dibenzoyloxy-4β-hydroxy-dihydro-β-agarofuran), salaterpene B (2) (1α,2β,8β-triacetoxy-9β-benzoyloxy-6β-cinnamoyloxy-4β-hydroxy-dihydro-β-agarofuran), salaterpene C (3) (1α,2β-diacetoxy-6β,9β-dibenzoyloxy-4β-hydroxy-dihydro-β-agarofuran) and salaterpene D (4) (2β-acetoxy-1α,6β-dibenzoyloxy-4β-hydroxy-9β-nicotinoyloxy-dihydro-β-agarofuran) together with two known compounds (5 and 6). The structures of the compounds were established by means of NMR spectroscopy. Compounds 1–4 and 6 were tested in vitro for their antiplasmodial activity against Plasmodium falciparum chloroquine-resistant strain W2. All the tested compounds exhibited a moderate potency with IC₅₀ below 2.7 μM.     

Diterpenoids from the stems of Tripterygium hypoglaucum (Celastraceae) and cytotoxic evaluation

Four new diterpenoids, 2α,16α-hydroxy-ent-kauran-19,20-olide (1), isopimara-8(14),15-diene-11β,19-diol (2), isopimara-8(14),15-diene-12α,19-diol (3), and 3-oxo-14,15-dihydroxyabieta-8,11,13-trien-19-ol (4), along with seven known compounds (5–11) were isolated from Tripterygium hypoglaucum. Their structures were established on the basis of extensive spectroscopic analysis. Triptolide (5) and 2-epitripdiolide (6) showed significant cytotoxicity against A549, DU145, KB, KBvin and MDA-MB-231 cell lines with IC₅₀ values of 0.0012–0.1306 μM in vitro.     

Isolation and structure of mortonol A,a possible biogenetic sesquiterpene precursor of mortonins A,C and D

The structure of mortonol A isolated from Mortonia greggii was established as a benzoate diester of 1α,4β,9β-trihydroxy-dihydroagarofurane-6-one. Its structure and stereochemistry were determined by chemical and spectroscopic means.     

Evaluation of Cytotoxicity and Antifungal Activity of Friedelanes from Salacia elliptica Roots

Plants from Salacia genus are used in traditional medicine for a wide range of diseases. Previous studies reported bioactive pentacyclic triterpenoids from S. elliptica leaves and branches. In this study, the novel pentacyclic triterpenoid 7α,15α-dihydroxyfriedelan-3-one ( 1 ) was obtained from the roots of Salacia elliptica, along with seven known compounds: friedelan-3-one ( 2 ), friedelan-3β-ol ( 3 ), friedelan-1,3-dione ( 4 ), friedelan-3,15-dione ( 5 ), 15α-hydroxyfriedelan-3-one ( 6 ), 15α,26-dihydroxyfriedelan-3-one ( 7 ), and 26-hydroxyfriedelan-3,15-dione ( 8 ). Additionally, one steroid, spinasterol ( 9 ), was also identified. The chemical structures of all compounds were established through ¹H and ¹³C-NMR. Compound 1 was analysed by additional 2D experiments (HMBC, HSQC, COSY, and NOESY) for complete elucidation. Furthermore, the cytotoxicity of compounds 2 , 3 , 6 , 7 and 8 against the A549 lung cancer cells model was evaluated. The flow cytometry analysis revealed a significant cytotoxic activity similar to that exhibited by the triterpenoid lupeol. Additionally, compounds 2 , 3 , 6 , and 7 were tested for in vitro antifungal activity against Candida, Cryptococcus and Sporothrix strains. However, all compounds showed no activity at the tested concentrations.     

A revised structure for the triterpene rigidenol

The structure of the triterpene rigidenol has been revised to 11α-hydroxy-lup-20(30)-en-3-one.     

New sesquiterpenoid alkaloids from Euonymus europea

Two new minor alkaloids from seeds of Euonymus europea L. have been characterised as 2-deacetylevonine and 2,5-bisdeacetylevonine by NMR. A selective one-step 5-deacetylation-bromobenzylation reaction of evonine is reported.     

Friedelin,D:A-friedo-olean-3,21-dione and 21α-hydroxy-D:A-friedo-olean-3-one from Kokoona zeylanica

Three triterpenes obtained from the inner bark of Kokoona zeylanica have been identified as friedelin, D:A-friedo-olean-3, 21-dione and 21α-hydroxy- D:A-friedo-olean-3-one by spectroscopic properties and chemical interconversions. Their chemotaxonomic significance is emphasized.     

Agarofuran sesquiterpenes from Schaefferia argentinensis

Sixteen dihydro-β-agarofuran sesquiterpenes were isolated from the aerial parts of Schaefferia argentinensis Speg. Their structures were determined by a combination of 1D and 2D NMR and MS techniques. The in vitro antiproliferative activity of the major sesquiterpenes was examined in T47D, MCF7, and MDA-MB231 human cancer cell lines, but was found to be marginal.