Aki Ishiyama

Selective and Potent in Vitro Antitrypanosomal Activities of Ten Microbial Metabolites

More than 400 compounds isolated from soil microorganisms, and catalogued in the antibiotic library of the Kitasato Institute for Life Sciences, were screened against African trypanosomes. Ten compounds were found to have selective and potent antitrypanosomal activity in vitro: aureothin, cellocidin, destomycin A, echinomycin, hedamycin, irumamycin, LL-Z 1272β, O-methylnanaomycin A, venturicidin A and virustomycin A. Results of the in vitro assays using the GUTat 3.1 strain of Trypanosomal brucei brucei and the STIB900 strain of T. b. rhodesiense are presented. Cytotoxicity was determined using a human MRC-5 cell line. This is the first report of antitrypanosomal activities of the 10 microbial metabolites listed above.

Spoxazomicins A–C, novel antitrypanosomal alkaloids produced by an endophytic actinomycete, Streptosporangium oxazolinicum K07-0460 T

Three novel antitrypanosomal alkaloids, named spoxazomicins A–C, were isolated by silica gel column chromatography and HPLC from the culture broth of a new endophytic actinomycete species, Streptosporangium oxazolinicum K07-0460T. The structures of the spoxazomicins were elucidated by NMR and X-ray crystal analyses and shown to be new types of pyochelin family antibiotic. Spoxazomicin A showed potent and selective antitrypanosomal activity with an IC50 value of 0.11 μg ml−1 in vitro without cytotoxicity against MRC-5 cells (IC50=27.8 μg ml−1).

Acylated pregnane glycosides from Caralluma tuberculata and their antiparasitic activity.

Five pregnane glycosides were isolated from Caralluma tuberculata (1-5), in addition to a known one (russelioside E, 6). The structures of the isolated compounds were elucidated by the analysis of NMR data and FAB-MS experiments. All the isolated compounds were tested for their antimalarial and antitrypanosomal activities as well as their cytotoxicity against human diploid embryonic cell line (MRC5).

Generation of Anti-trypanosomal Agents through Concise Synthesis and Structural Diversification of Sesquiterpene Analogues

To access high-quality small-molecule libraries to screen lead candidates for neglected diseases exemplified by human African trypanosomiasis, we sought to develop a synthetic process that would produce collections of cyclic scaffolds relevant to an assortment of natural products exhibiting desirable biological activities. By extracting the common structural features among several sesquiterpenes, including artemisinin, anthecularin, and transtaganolides, we designed six types of scaffolds with systematic structural variations consisting of three types of stereochemical relationships on the sp(3) ring-junctions and two distinct arrays of tricyclic frameworks. A modular and stereodivergent assembly of dienynes exploiting a versatile manifold produced a series of cyclization precursors. Divergent cyclizations of the dienynes employing tandem ring-closing metathesis reactions overrode variant reactivities of the cyclization precursors, leading to the six canonical sets of the tricyclic scaffolds incorporating a diene group. Screenings of trypanosomal activities of the canonical sets, as well as regio- and stereoisomers of the tricyclic dienes, allowed generation of several anti-trypanosomal agents defining the three-dimensional shape of the pharmacophore. The candidate tricyclic dienes were selected by primary screenings and further subjected to installation of a peroxide bridge, which generated artemisinin analogues that exhibited potent in vitro anti-trypanosomal activities comparable or even superior to those of artemisinin and the approved drugs, suramin and eflornithine.

In vitro antitrypanosomal activity of plant terpenes against Trypanosoma brucei.

During the course of screening to discover antitrypanosomal compounds, 24 known plant terpenes (6 sesquiterpenes, 14 sesquiterpene lactones and 4 diterpenes) were evaluated for in vitro antitrypanosomal activity against Trypanosoma brucei brucei. Among them, 22 terpenes exhibited antitrypanosomal activity. In particular, α-eudesmol, hinesol, nardosinone and 4-peroxy-1,2,4,5-tetrahydro-α-santonin all exhibited selective and potent antitrypanosomal activities in vitro. Detailed here in an in vitro antitrypanosomal properties and cytotoxicities of the 24 terpenes compared with two therapeutic antitrypanosomal drugs (eflornithine and suramin). This finding represents the first report of promising trypanocidal activity of these terpenes. Present results also provide some valuable insight with regard to structure-activity relationships and the possible mode of action of the compounds.

Merobatzelladines A and B, Anti-Infective Tricyclic Guanidines from a Marine Sponge Monanchora sp.

Merobatzelladines A (1) and B (2) have been isolated from a marine sponge Monanchora sp. as antibacterial constituents. Their structures including relative stereochemistry were determined by interpretation of spectral data. The absolute stereochemistry of merobatzelladine B (2) was elucidated after introduction of the fourth ring system preinstalled with a secondary hydroxyl group to which the modified Mosher method was applied. Merobatzelladines exhibit moderate anti-infective activity against a bacterium and protozoa.

In vitro and in vivo antimalarial activity of puberulic acid and its new analogs, viticolins A–C, produced by Penicillium sp. FKI-4410

In the course of screening for antimalarial agents, five tropolone compounds were isolated from the culture broth of Penicillium sp. FKI-4410. Two were known compounds, puberulic acid and stipitatic acid. Three were new analogs of puberulic acid, designated viticolins A–C. Among them, puberulic acid exhibited potent antimalarial inhibition, with IC50 values of 0.01 μg ml−1 against chloroquine-sensitive and -resistant Plasmodium falciparum strains in vitro. Furthermore, puberulic acid showed weak cytotoxicity against human MRC-5 cells, with an IC50 value of 57.2 μg ml−1. The compound also demonstrated a therapeutic effect in vivo, which compared well against the currently used antimalarial drugs, and thus shows promise as a leading candidate for development into a new antimalarial compound.

Mangromicins A and B: structure and antitrypanosomal activity of two new cyclopentadecane compounds from Lechevalieria aerocolonigenes K10-0216.

Two new cyclopentadecane antibiotics, named mangromicins A and B, were separated out from the culture broth of Lechevalieria aerocolonigenes K10-0216 by Diaion HP-20, silica gel and ODS column chromatography, and were finally purified by HPLC. The chemical structures of the two novel compounds were elucidated by instrumental analyses, including various NMR, MS and X-ray crystallography. Mangromicins A and B consist of cyclopentadecane skeletons with a tetrahydrofuran unit and a 5,6-dihydro-4-hydroxy-2-pyrone moiety. Mangromicins A and B showed in vitro antitrypanosomal activity with IC50 values of 2.4 and 43.4 μg ml−1, respectively. The IC50 values of both compounds were lower than those of cytotoxicity against MRC-5 human fetal lung fibroblast cells.

Promising lead compounds for novel antiprotozoals

Malaria and human African trypanosomiasis (HAT), also known as sleeping sickness, are devastating diseases caused by infection with the protozoan parasites of the Plasmodia and Trypanosoma genera, respectively. The diseases infect millions of people. HAT, caused by infection with Trypanosoma brucei, is a complex disease and represents a major cause of morbidity and mortality in sub-Saharan Africa, where it is endemic and an estimated 70 million people are at risk of contracting it. Several epidemics of HAT occurred during the last century, but a combination of vector control, disease surveillance and early drug treatment of those infected caused the disease to almost disappear by the mid-1960s. Over the following 2–3 decades the disease re-emerged, but recent control efforts have again reduced its incidence, annual cases totaling an estimated 50 000–70 000. HAT has two distinct forms (gambiense and rhodesiense) depending on the parasite involved, each form having two specific stages. HAT is fatal if left untreated, with treatment depending on the stage of the disease. Drugs for the early-stage (pentamidine and suramin) are well tolerated, easier to administer and more effective. Drugs used for the latestage (melarsoprol, and eflornithine which is ineffective for the acute rhodesiense form) have to cross the blood–brain barrier. They are toxic (particularly melarsoprol), often causing severe and sometimes fatal side effects, and have to be administered under costly medical supervision. Consequently, the swift development and introduction of safer, more effective, easy-to-use and affordable drugs will be instrumental in helping to achieve recent initiatives aimed at eliminating the disease as a public health problem. Unlike HAT, which is restricted to Africa, malaria is widespread globally, with an estimated 3.5 billion people at risk of contracting the disease, 1.3 billion of whom are at high risk. Massive recent global initiatives to combat the disease, integrating vector control, prevention and treatment, have resulted in significant progress. Nevertheless, some 243 million cases occurred in 2008, resulting in an estimated 863 000 deaths, almost 90% of which were in Africa. 1 Many anti

Borrelidin, a potent antimalarial: stage-specific inhibition profile of synchronized cultures of Plasmodium falciparum

Borrelidin, a potent antimalarial: stage-specific inhibition profile of synchronized cultures of Plasmodium falciparum