Wayne D. Inman

A β-Carboline Alkaloid from the Papua New Guinea Marine Sponge Hyrtios reticulatus

A new 1-imidazoyl-3-carboxy-6-hydroxy-beta-carboline alkaloid, named hyrtiocarboline (1), was isolated from a Papua New Guinea marine sponge, Hyrtios reticulatus. The structure was elucidated from spectroscopic data, including (1)H-(15)N HMBC NMR experiments, which provided complementary (15)N chemical shift information in support of the structure. This compound showed selective antiproliferative activity against H522-T1 non-small cell lung, MDA-MB-435 melanoma, and U937 lymphoma cancer cell lines.

Natural Product Libraries to Accelerate the High Throughput Discovery of Therapeutic Leads

A high-throughput (HT) paradigm generating LC-MS-UV-ELSD-based natural product libraries to discover compounds with new bioactivities and or molecular structures is presented. To validate this methodology, an extract of the Indo-Pacific marine sponge Cacospongia mycofijiensis was evaluated using assays involving cytoskeletal profiling, tumor cell lines, and parasites. Twelve known compounds were identified including latrunculins (1-4, 10), fijianolides (5, 8, 9), mycothiazole (11), aignopsanes (6, 7), and sacrotride A (13). Compounds 1-5 and 8-11 exhibited bioactivity not previously reported against the parasite T. brucei, while 11 showed selectivity for lymphoma (U937) tumor cell lines. Four new compounds were also discovered including aignopsanoic acid B (13), apo-latrunculin T (14), 20-methoxy-fijianolide A (15), and aignopsane ketal (16). Compounds 13 and 16 represent important derivatives of the aignopsane class, 14 exhibited inhibition of T. brucei without disrupting microfilament assembly, and 15 demonstrated modest microtubule-stabilizing effects. The use of removable well plate libraries to avoid false positives from extracts enriched with only one or two major metabolites is also discussed. Overall, these results highlight the advantages of applying modern methods in natural products-based research to accelerate the HT discovery of therapeutic leads and/or new molecular structures using LC-MS-UV-ELSD-based libraries.

Synthesis, conformational analysis, and antimalarial activity of tricyclic analogs of artemisinin

Abstract Aspects of synthesis, conformational analysis, and antimalarial activity of artemisinin analogs (±)-5-nor-6-desmethyl-4,5-secoartemisinin (2), (−)-5-nor-4,5-secoartemisinin (3), (+)-4,5-secoartemisinin (4), and (+)-4,5-desethano-artemisinin (5)22 are described. The conformations of these multicyclic structures were determined through a combination of X-ray crystallography, NMR, and computational analysis, with an emphasis on the 1,2,4-trioxane geometry. Two major solution conformations for both 2 and 3 were found: all chair forms 2a and 3a, and twist-boat/twist-boat/chair forms 2b and 3b, respectively. The major solution conformer 2a matched the solid state structure found via X-ray crystallography. Computations suggest that (+)-4,5-Secoartemisinin (4) has three conformations of equal energy: chair/twist-boat, 4a, twist-boat/twist-boat/chair, 4b, corresponding to the X-ray crystal structure, and twist boat/chair/chair, 4c. The 1,2,4-trioxane and lactone rings adopt the twist-boat conformations in 2b, 3b, 4a, and 4c. When compared to artemisinin, these tricyclic, flexible analogs have different geometry yet retain some in vitro antimalarial activity against resistant strains of Plasmodium falciparum. Possible structure/activity correlations are discussed.

Additional Insights on the Bastadins: Isolation of Analogues from the Sponge Ianthella cf. reticulata and Exploration of the Oxime Configurations†

The focus of this study is on the bastadin class of bromotyrosine derivatives, commonly isolated from Ianthella marine sponges, and is the first report on the secondary metabolites from Ianthella cf. reticulata. Two new bastadins were isolated, (E,Z)-bastadin 19 (1a), a diastereoisomer of the known (E,E)-bastadin 19 (1b), and dioxepine bastadin 3 (2), an unusual dibenzo-1,3-dioxepine. A bastadin NMR database was created and assisted in the structure determination of 1b and 2 and the rapid dereplication of 10 other known compounds including bastadins 2-9 (3-10), 13 (11), and 19 (1a). The geometry of the 2-(hydroxyimino)-N-alkylamide chains, a chemical feature present in all bastadins, was further probed, and new insights regarding the natural oxime configuration are discussed. Bastadins possessing (E,Z)-, (Z,E)-, or (E,E)-dioxime configurations could be artifacts of isolation or storage in solution. Therefore, this point was explored by photochemical and thermal isomerization studies, as well as molecular mechanics calculations. Bastadins 13 (11) and 19 (1a) exhibited moderate inhibition against Trypanosoma brucei, and bastadin 4 (5) was cytotoxic to HCT-116 colon cancer cells.

Lipophilic stinging nettle extracts possess potent anti-inflammatory activity, are not cytotoxic and may be superior to traditional tinctures for treating inflammatory disorders.

Extracts of four plant portions (roots, stems, leaves and flowers) of Urtica dioica (the stinging nettle) were prepared using accelerated solvent extraction (ASE) involving water, hexanes, methanol and dichloromethane. The extracts were evaluated for their anti-inflammatory and cytotoxic activities in an NF-κB luciferase and MTT assay using macrophage immune (RAW264.7) cells. A standardized commercial ethanol extract of nettle leaves was also evaluated. The methanolic extract of the flowering portions displayed significant anti-inflammatory activity on par with a standard compound celastrol (1) but were moderately cytotoxic. Alternatively, the polar extracts (water, methanol, ethanol) of the roots, stems and leaves displayed moderate to weak anti-inflammatory activity, while the methanol and especially the water soluble extracts exhibited noticeable cytotoxicity. In contrast, the lipophilic dichloromethane extracts of the roots, stems and leaves exhibited potent anti-inflammatory effects greater than or equal to 1 with minimal cytotoxicity to RAW264.7 cells. Collectively these results suggest that using lipophilic extracts of stinging nettle may be more effective than traditional tinctures (water, methanol, ethanol) in clinical evaluations for the treatment of inflammatory disorders especially arthritis. A chemical investigation into the lipophilic extracts of stinging nettle to identify the bioactive compound(s) responsible for their observed anti-inflammatory activity is further warranted.

Unraveling the bastarane and isobastarane oximo amide configurations and associated macrocycle conformations: implications of their influence on bioactivities.

Our rigorous re-examination of the conformational properties of bastadins that comprise the isobastarane and bastarane-type macrocycle has generated some interesting new insights. We determined that these macrocycles are flexible and possess a surprising degree of reflection symmetry that generates enantiomeric conformations. The macrocycle symmetry arises from its ability to twist in a disrotatory fashion, providing one set of conformers, and then twists with the opposite disrotation to generate a corresponding set of enantiomers. Overall, the isobastarane conformations for (E,E)-bastadin 19 (1a) are complex and can access several distinct ring conformations. In contrast, the bastarane macrocycle in bastadin 5 (2) and bastadin 6 (3) maintains a similar overall shape. We postulate that the short-term stability of the (Z)-oximo amide, an uncommon configuration found in bastadins and psammaplins, is due to the existence of conformers with intramolecular hydrogen bonds involving the (Z)-oxime, and hydrogen bonding impedes oxime isomerization to the more stable (E)-oximo amide in solution. Finally, the modeling results provided insights toward understanding the different antiproliferative activity against endothelial cells as well as Ca(2+) channel modulation activities attributed to bastaranes 2 and 3 versus isobastarane 1a.