Ayumi Tsutsui

Exclusive formation of imino[4 + 4]cycloaddition products with biologically relevant amines: plausible candidates for acrolein biomarkers and biofunctional modulators

We synthetically demonstrate that eight-membered heterocycles, namely, 2,6,9-triazabicyclo[3.3.1]nonanes and 1,5-diazacyclooctanes, are the exclusive products of the reaction of acrolein with biologically relevant amines via an imino[4 + 4]cycloaddition. These compounds are produced in much higher amounts and efficiencies than the acrolein biomarker in current use, 3-formyl-3,4-dehydropiperidine (FDP). Our results not only indicate that eight-membered heterocycles may potentially be used as new biomarkers, but also strongly suggest the involvement of these heterocycles in various important biological phenomena, e.g., an acrolein-mediated mechanism underlying oxidative stress.

1,5‐Diazacyclooctanes, as Exclusive Oxidative Polyamine Metabolites, Inhibit Amyloid‐β(1‐40) Fibrillization

Biologically relevant 1,5‐diazacyclooctanes derived from polyamines and acrolein, inhibit Aβ40 peptide fibrillization and significantly suppress cell cytotoxicity. Formal [4+4] cycloaddition reaction of imines is thus involved in modulating oxidative stress processes associated with neural diseases.

Antimalarial C-9 oxime derivatives from desmycosin, produced by click chemistry

Plasmodium falciparum parasites remain the major cause of malaria, a serious and potentially fatal infectious disease worldwide, despite the intermittent introduction of several different successive classes of potent and effective drugs. According to the World Health Organization’s Malaria Report (2011), an estimated 3.3 billion people were still at risk of malaria in 2010.1 Worldwide, in 2010, 99 countries and territories reported ongoing malaria transmission and a further 7 countries were trying to prevent the reintroduction of the disease, comprising a total of 106 countries in which malaria was considered endemic.1 The prevention and successful treatment of malaria is heavily dependent on antimalarial drugs. Chloroquine proved to be a remarkable safer, cheap and extremely effective antimalarial drug, serving as the frontline antimalarial treatment from its introduction in the mid-1940s to the 1990s.2 However, the malaria parasite has continually proved to be particularly efficient at developing resistance to virtually all drugs used to control it. Chloroquine-resistant parasites quickly emerged and spread worldwide, rendering the drug useless in many locations. The same scenario is being witnessed with the latest in the long line of potent antimalarials, artemisinin. Therefore, there is a continuing need for new antimalarial drugs that are effective, safe, affordable and easy to use and which, ideally, have a novel mode of action. In our institute, we have focused on the screening and synthesis of antimalarial agents from microbial metabolites including antibacterial macrolides.3–5 In 2007, azithromycin, a 15-membered antibacterial macrolide, was found to possess potent antimalarial activity by Fidock and co-workers.6 Azithromycin is a slow-acting antimalarial that targets the parasite apicoplast and its prokaryotic ribosomes. The effects of its action increase with prolonged incubation time (from one to two generations), giving an IC50 in the nano-molar range. Continuously, new derivatives of azithromycin have been developed with the aim to improve activity and selectivity for the malaria parasite.7 Another macrolide antibiotic, tylosin, was first isolated by McGuire and co-workers8 in 1961, and is a 16-membered macrolide isolated from a culture broth of Streptomyces fradiae. In 1984, McColm and McHardy9 reported that tylosin demonstrated antimalarial activity against P. falciparum strain Liverpool (IC501⁄4 0.1mg ml 1). However, there have been no subsequent reports concerning the antimalarial activity of tylosin or its derivatives. In this short note, we report that novel C-9 oximes of desmycosin express antimalarial activity against chloroquine-resistant P. falciparum K110 malaria parasites. The removal of mycarose from tylosin can be accomplished under mild acidic hydrolysis to give desmycosin, a known minor component in the fermentation broth of the tylosin-producing strain.11 The antimicrobial activity of desmycosin is potent but slightly lower than that of tylosin, but it has almost no efficacy in vivo when given orally.11 Likewise, C-9 oxime derivatives of tylosin and desmycosin have been evaluated in bioassays, but did not show better antimicrobial activity than tylosin.12 Our work on tylosin analog synthesis produced C-9 oximes of desmycosin (3, 6 and 7), prepared from dimethoxydesmycosin (1)13 by oxime formation with corresponding hydroxylamines HCl14 and acid hydrolysis of dimethoxyacetal moiety in good yields, respectively. These analogs showed antimicrobial activities, similar to or slightly lower than that of desmycosin, (Scheme 1, Table 1). We specifically tested for antimalarial activity in all new analogs derived from tylosin. Moreover, as the discovery of the antimicrobial alkyne-bearing lead compounds (6 and 7) for antimicrobial activities, our efforts have focused on the preparation of new analogs in this series utilizing ‘click chemistry’, which provides an important approach for simple and rapid evaluation of functional activity. The concept of ‘click chemistry’ was originally introduced by Kolb, Finn and Sharpless in 2001.15 It incorporates powerful and selective reactions for efficient synthesis of interesting compounds and combinatorial libraries through heteroatom links. The advantages of ‘click chemistry’ in biological studies of macrolides have recently been clearly demonstrated in our laboratory.16,17 The alkyne-bearing oximes (6 and 7) are intermediates allowing generation of targeted triazole compounds. Anti-selective triazole formation was carried out with a catalytic amount of Cu(MeCN)4PF6

BOROMYCIN DERIVATIVES: SYNTHESIS AND ANTIMALARIAL ACTIVITY IN VITRO AND IN VIVO

Derivatives of boromycin, which has significant antimalarial properties both in vitro and in vivo, were examined for similar the efficacy against both drug-resistance strain and drug-sensitive strain of malaria and as a means to elucidate structure-activity relationships. More potent in vitro compounds tended to lose their properties in vivo when administered orally. Some novel 16-O-acyl derivatives were found to be more potent and selective antimalarial compounds compared to boromycin. Furthermore, alkyne-bearing 16-O-alkylacyl compounds retained reasonably good efficacy in vivo when given per os.

5-O-Mycaminosyltylonolide antibacterial derivatives: design, synthesis and bioactivity

Tylosin is a 16-membered macrolide broad-spectrum antibiotic that has an important role in veterinary medicine, active against Gram-positive and a restricted range of Gram-negative bacteria. We synthesized 15 types of tylosin-related derivatives by chemical modification and evaluated them against mastitis pathogens. Among them, 20-deoxy-20-{N-methyl-N-[1-(3-quinolyl)-1H-1,2,3-triazol-4-yl]methylamino}-5-O-mycaminosyltylonolide 2f and 20-deoxy-20-{N-benzyl-N-[1-(3-quinolyl)-1H-1,2,3-triazol-4-yl]methylamino}-5-O-mycaminosyltylonolide 2k were found to not only expand their antibacterial impact to include Gram-negative bacteria, such as Escherichia coli and Klebsiella pneumoniae, but also to retain or increase antibacterial activity against Gram-positive bacteria, such as Staphylococcus aureus and Streptococcus uberis in comparison with the parent tylosin.