Christopher A. Gray

The absolute stereochemistry of a diterpene from Ballota aucheri.

The semi-synthetic transformation of hispanolone, isolated from Ballota africana, into 6beta-hydroxy-15,16-epoxylabda-8,13(16),14-trien-7-one has established an ent-labdane absolute stereochemistry for a diterpene metabolite originally isolated from B. aucheri.

Labdane Diterpenes From the South African Marine Pulmonate Trimusculus Costatus

Abstract The endemic South African marine pulmonate gastropod Trimusculus costatus yielded two labdane diterpenes, the known 6β,7a-diacetoxylab-8,13-dien-15-ol (1), and the new 2α,6β,7a-triacetoxylabda-8,13-dien-15-ol (2). Standard spectroscopic methods were used to establish the structures of these compounds which were both toxic to Artemia salina and inhibited feeding of the predatory fish Pomadasys commersonnii.

Bioactive metabolites from the South African marine mollusk Trimusculus costatus.

A reinvestigation of extracts of the endemic South African intertidal limpet Trimusculus costatus yielded the known labdane diterpenes 6beta,7alpha-diacetoxylabda-8,13 E-dien-15-ol ( 1) and 2alpha,6beta,7alpha-triacetoxylabda-8,13 E-dien-15-ol ( 2) and three new metabolites, 6beta,7alpha,15-triacetoxylabda-8,13 E-diene ( 3), 3alpha,11-dihydroxy-9,11-seco-cholest-4,7-dien-6,9-dione ( 4), and cholest-7-en-3,5,7-triol ( 5). Chiral derivatization and X-ray analysis were used to confirm the labdane absolute configuration of 2. Compounds 1, 2 and 4 exhibited moderate activity (3-25 microM) against the WHCO1 human esophageal cancer cell line.

An improved synthesis of rhinocerotinoic acid

Abstract The stereoselective synthesis of E -rhinocerotinoic acid has been achieved in five steps from (−)-sclareol in an overall yield of 32%. This constitutes a significant improvement on the previous synthesis of this anti-inflammatory compound.

Macroalgal Endophytes from the Atlantic Coast of Canada: A Potential Source of Antibiotic Natural Products?

As the need for new and more effective antibiotics increases, untapped sources of biodiversity are being explored in an effort to provide lead structures for drug discovery. Endophytic fungi from marine macroalgae have been identified as a potential source of biologically active natural products, although data to support this is limited. To assess the antibiotic potential of temperate macroalgal endophytes we isolated endophytic fungi from algae collected in the Bay of Fundy, Canada and screened fungal extracts for the presence of antimicrobial compounds. A total of 79 endophytes were isolated from 7 species of red, 4 species of brown, and 3 species of green algae. Twenty of the endophytes were identified to the genus or species level, with the remaining isolates designated codes according to their morphology. Bioactivity screening assays performed on extracts of the fermentation broths and mycelia of the isolates revealed that 43 endophytes exhibited antibacterial activity, with 32 displaying antifungal activity. Endophytic fungi from Bay of Fundy macroalgae therefore represent a significant source of antibiotic natural products and warrant further detailed investigation.

The X-ray crystal structures of ambraketal and 8-epi-ambraketal

The crystal structures of ambraketal and 8-epi-ambraketal, synthesised in five steps from (–)-sclareol, are reported.

Dibenz[b,f]oxepin and Antimycobacterial Chalcone Constituents of Empetrum nigrum

Two new dibenz[b,f]oxepins, empetroxepins A and B (1 and 2), and seven known compounds (3-9) were isolated from an extract of the Canadian medicinal plant Empetrum nigrum that significantly inhibited the growth of Mycobacterium tuberculosis H37Ra. The structures of 1 and 2 were established through analysis of NMR and MS data. The antimycobacterial activity of the plant extract was attributed primarily to the presence of two chalcone derivatives (6 and 7) that exhibited selective antimycobacterial activity (IC50 values of 23.8 and 32.8 μM, respectively) in comparison to mammalian (HEK 293) cells (IC50 values of 109 and 249 μM, respectively).

Chromone studies. Part 11. Synthesis and electron-impact mass spectrometric study of granulosin and side-chain analogues

Granulosin, a chromone constituent of the bark of Galipea granulosa, and four analogues, all of which exhibit toxicity to the brine shrimp Artemia salina, have been prepared from 2′,3′,4′-trihydroxyacetophenone. High-resolution mass spectrometric analysis has permitted elucidation of the fragmentation patterns exhibited by these systems following electron-impact ionisation.