Enantioselective Total Synthesis of Eurylene, 14-Deacetyl Eurylene, and Their 11-Epimers: The Relation between Ionophoric Nature and Cytotoxicity

The direct oxidative diene cyclization and related reactions in natural product synthesis

The direct oxidative cyclization of 1,5-dienes is a valuable synthetic method for the (dia)stereoselective preparation of substituted tetrahydrofurans. Closely related reactions start from 5,6-dihydroxy or 5-hydroxyalkenes to generate similar products in a mechanistically analogous manner. After a brief overview on the history of this group of transformations and a survey on mechanistic and stereochemical aspects, this review article provides a summary on applications in natural product synthesis. Moreover, current limitations and future directions in this area of chemistry are discussed.

Review on a Traditional Herbal Medicine, Eurycoma longifolia Jack (Tongkat Ali): Its Traditional Uses, Chemistry, Evidence-Based Pharmacology and Toxicology

Eurycoma longifolia Jack (known as tongkat ali), a popular traditional herbal medicine, is a flowering plant of the family Simaroubaceae, native to Indonesia, Malaysia, Vietnam and also Cambodia, Myanmar, Laos and Thailand. E. longifolia, is one of the well-known folk medicines for aphrodisiac effects as well as intermittent fever (malaria) in Asia. Decoctions of E. longifolia leaves are used for washing itches, while its fruits are used in curing dysentery. Its bark is mostly used as a vermifuge, while the taproots are used to treat high blood pressure, and the root bark is used for the treatment of diarrhea and fever. Mostly, the roots extract of E. longifolia are used as folk medicine for sexual dysfunction, aging, malaria, cancer, diabetes, anxiety, aches, constipation, exercise recovery, fever, increased energy, increased strength, leukemia, osteoporosis, stress, syphilis and glandular swelling. The roots are also used as an aphrodisiac, antibiotic, appetite stimulant and health supplement. The plant is reported to be rich in various classes of bioactive compounds such as quassinoids, canthin-6-one alkaloids, β-carboline alkaloids, triterpene tirucallane type, squalene derivatives and biphenyl neolignan, eurycolactone, laurycolactone, and eurycomalactone, and bioactive steroids. Among these phytoconstituents, quassinoids account for a major portion of the E. longifolia root phytochemicals. An acute toxicity study has found that the oral Lethal Dose 50 (LD50) of the alcoholic extract of E. longifolia in mice is between 1500-2000 mg/kg, while the oral LD50 of the aqueous extract form is more than 3000 mg/kg. Liver and renal function tests showed no adverse changes at normal daily dose and chronic use of E. longifolia. Based on established literature on health benefits of E. longifolia, it is important to focus attention on its more active constituents and the constituents' identification, determination, further development and most importantly, the standardization. Besides the available data, more evidence is required regarding its therapeutic efficacy and safety, so it can be considered a rich herbal source of new drug candidates. It is very important to conserve this valuable medicinal plant for the health benefit of future generations.

Comparative perspective and synthetic applications of transition metal mediated oxidative cyclisation of 1,5-dienes towards cis-2,5-disubstituted tetrahydrofurans

Synthesis ofcis-2,5-disubstituted tetrahydrofuran rings from 1,5-diene precursors using metal-oxo species along with their mechanistic proposals and synthetic applications is concisely reviewed.

Synthetic endeavours towards oxasqualenoid natural products containing 2,5-disubstituted tetrahydrofurans – eurylene and teurilene

Given the unique structural features of oxasqualenoid natural products and their cytotoxicity, representative examples from oxasqualenoids, eurylene and teurilene have been briefly reviewed. Both compounds possess cis- and trans-2,5-disubstituted tetrahydrofuran rings and represent chiral and achiral facets found in this class of natural products.

Enantioselective formal synthesis of eurylene: synthesis of the cis- and trans-THF fragments using oxidative cyclization

A formal synthesis of eurylene is described, where both cis- and trans-THF-containing fragments were prepared using diastereo- and chemoselective permanganate-mediated oxidative monocyclizations of trienes.

Bacterial cytoplasmic membrane permeability assay using ion-selective electrodes

We used K(+) and tetraphenylphosphonium (TPP(+)) electrodes simultaneously to evaluate the ability of antimicrobial peptides to form channels (or more generally to increase permeability) and to abolish membrane potential in bacterial cytoplasmic membranes in situ. Such evaluations are usually made independently by colorimetric monitoring of the hydrolysis of a chromogenic substrate by a cytoplasmic enzyme or by fluorimetric determination of membrane depolarization using a membrane potential-sensitive dye. In the present study, the K(+) electrode was used to evaluate channel-forming ability by monitoring the efflux of K(+) originally present in the cytoplasm of bacteria, while the TPP(+) electrode was used to examine membrane depolarization causing the efflux of TPP(+) accumulated in the cytoplasm of bacteria dependent on membrane potential. Thus, the combination of these two electrodes enabled us to clarify how the peptide-induced formation of ion channels is involved in disrupting the energy-generating system in situ.