Yoshihiko Kobayashi

Amycolamicin: A Novel Broad‐Spectrum Antibiotic Inhibiting Bacterial Topoisomerase

The abuse of antibacterial drugs imposes a selection pressure on bacteria that has driven the evolution of multidrug resistance in many pathogens. Our efforts to discover novel classes of antibiotics to combat these pathogens resulted in the discovery of amycolamicin (AMM). The absolute structure of AMM was determined by NMR spectroscopy, X-ray analysis, chemical degradation, and modification of its functional groups. AMM consists of trans-decalin, tetramic acid, two unusual sugars (amycolose and amykitanose), and dichloropyrrole carboxylic acid. The pyranose ring named as amykitanose undergoes anomerization in methanol. AMM is a potent and broad-spectrum antibiotic against Gram-positive pathogenic bacteria by inhibiting DNA gyrase and bacterial topoisomerase IV. The target of AMM has been proved to be the DNA gyrase B subunit and its binding mode to DNA gyrase is different from those of novobiocin and coumermycin, the known DNA gyrase inhibitors.

α-Hydrogen elimination in some carbohydrate triflates

Abstract Treatment of 1,2;5,6- di -O- isopropylidene -3-O- triflyl- d -gluco- and d -allo-furanoses (2 and 6) with MeLi (or BuLi) in diethyl ether afforded different products; the former gave a 3,4-unsaturated product (4), the latter a 3-methyl(or butyl)- d -allofuranose derivative (7, 8). Similar treatment of the 2-triflates (27, 30) of methyl 3-O-benzyl-4,6-O-benzylidene-α- and -β- d -glucopyranosides gave the corresponding 2-C-alkyl derivatives. The 3- and 4-triflates of similar pyranoside structures examined gave, in most cases, the corresponding unsaturated compounds. Both of the reactions (unsaturation and C-alkylation) are explained, in most cases, on the basis of α-elimination, that is, the reactions commenced with abstraction of the hydrogen attached to the carbon bearing a triflyloxy group, this fact being confirmed by studies with deuterated analogs. Transition states for these reactions were also studied by computer calculations.

A synthetic study of methyl 3-deoxy-3-fluoro-α-d-glucopyranosides from methyl 2,3-anhydro-α-d-allopyranosides, and synthesis of 3′-deoxy-3′-fluorokanamycin A and 3′-chloro-3′-deoxykanamycin A

Abstract Reactions of 4,6-disubstituted 2,3-anhydro-α- d -allopyranosides with potassium hydrogenfluoride (KHF 2 ) in ethane-1,2-diol gave, by oxirane-ring opening, the corresponding 2-deoxy-2-fluoro-α- d -altro- and 3-deoxy-3-fluoro-α- d -gluco-pyranosyl derivatives, with the latter always in preponderance. The influence of the substituents at C-4 and C-6 on the d - gluco — d - altro ( r ) have been studied by molecular mechanics, and the discrepancy between the experimental and calculated r values has been positively utilized to measure the effects of solvation and hydrogen bonding relative to the C-4 and C-6 substituents. By application of this reaction, 3′-deoxy-3′-fluorokanamycin A has been prepared by treatment of a 2′,3′-anhydro-3′-epikanamycin A derivative ( 35 ) with KHF 2 . 3′-Chloro-3′-deoxykanamycin A was also prepared.

Synthesis and antibacterial activity of 4″ or 6″-alkanoylamino derivatives of arbekacin.

Arbekacin, an aminoglycoside antibiotic, is an important drug because it shows a potent efficacy against methicillin-resistant Staphylococcus aureus. However, resistance to arbekacin, which is caused mainly by the bifunctional aminoglycoside-modifying enzyme, has been observed, becoming a serious problem in medical practice. To create new arbekacin derivatives active against resistant bacteria, we modified the C-4″ and 6″ positions of its 3-aminosugar portion. Regioselective amination of the 6″-position gave 6″-amino-6″-deoxyarbekacin (1), and it was converted to a variety of 6″-N-alkanoyl derivatives (6a−z). Furthermore, regioselective modifications of the 4″-hydroxyl group were performed to give 4″-deoxy-4″-epiaminoarbekacin (2) and its 4″-N-alkanoyl derivatives (12 and 13). Their antibacterial activity against S. aureus, including arbekacin-resistant bacteria, was evaluated. It was observed that 6″-amino-6″-N-[(S)-4-amino-2-hydroxybutyryl]-6″-deoxyarbekacin (6o) showed excellent antibacterial activity, even better than arbekacin.

New anti-cancer chemicals Ertredin and its derivatives, regulate oxidative phosphorylation and glycolysis and suppress sphere formation in vitro and tumor growth in EGFRvIII-transformed cells.

BackgroundEGFRvIII is a mutant form of the epidermal growth factor receptor gene (EGFR) that lacks exons 2–7. The resulting protein does not bind to ligands and is constitutively activated. The expression of EGFRvIII is likely confined to various types of cancer, particularly glioblastomas. Although an anti-EGFRvIII vaccine is of great interest, low-molecular-weight substances are needed to obtain better therapeutic efficacy. Thus, the purpose of this study is to identify low molecular weight substances that can suppress EGFRvIII-dependent transformation.MethodsWe constructed a new throughput screening system and searched for substances that decreased cell survival of NIH3T3/EGFRvIII spheres under 3-dimensional (3D)-culture conditions, but retained normal NIH3T3 cell growth under 2D-culture conditions. In vivo activity was examined using a mouse transplantation model, and derivatives were chemically synthesized. Functional characterization of the candidate molecules was investigated using an EGFR kinase assay, immunoprecipitation, western blotting, microarray analysis, quantitative polymerase chain reaction analysis, and measurement of lactate and ATP synthesis.ResultsIn the course of screening 30,000 substances, a reagent, “Ertredin” was found to inhibit anchorage-independent 3D growth of sphere-forming cells transfected with EGFRvIII cDNA. Ertredin also inhibited sphere formation in cells expressing wild-type EGFR in the presence of EGF. However, it did not affect anchorage-dependent 2D growth of parental NIH3T3 cells. The 3D-growth-inhibitory activity of some derivatives, including those with new structures, was similar to Ertredin. Furthermore, we demonstrated that Ertredin suppressed tumor growth in an allograft transplantation mouse model injected with EGFRvIII- or wild-type EGFR-expressing cells; a clear toxicity to host animals was not observed. Functional characterization of Ertredin in cells expressing EGFRvIII indicated that it stimulated EGFRvIII ubiquitination, suppressed both oxidative phosphorylation and glycolysis under 3D conditions, and promoted cell apoptosis.ConclusionWe developed a high throughput screening method based on anchorage-independent sphere formation induced by EGFRvIII-dependent transformation. In the course of screening, we identified Ertredin, which inhibited anchorage-independent 3D growth and tumor formation in nude mice. Functional analysis suggests that Ertredin suppresses both mitochondrial oxidative phosphorylation and cytosolic glycolysis in addition to promoting EGFRvIII degradation, and stimulates apoptosis in sphere-forming, EGFRvIII-overexpressing cells.

Discovery of 2-hydroxyarbekacin, a new aminoglycoside antibiotic with reduced nephrotoxicity

The emergence and spread of bacteria with resistance to antibacterial drugs in recent years is now considered a significant threat to global public health and the world economy.1, 2 In particular, the severe bacterial infections caused by methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa have become serious clinical problems because of increased antimicrobial resistance, as observed for vancomycin-resistant S. aureus and multi-drug resistant P. aeruginosa.3 Arbekacin4 (ABK), an aminoglycoside antibiotic, is efficacious against MRSA, and is commonly used to treat infected patients in the clinical setting. This semi-synthetic antibiotic is stable toward AAC(6′)-APH(2″), a bifunctional enzyme present in MRSA, and is also effective against almost all antibiotic-resistant bacteria that produce aminoglycoside-modifying enzymes.5 However, despite its superior antibacterial activity and stability toward aminoglycoside-modifying enzymes, treatment with ABK is limited because of its adverse effect on the kidneys.6, 7 Therefore, we have conducted synthetic studies on a number of ABK derivatives in an effort to decrease the associated toxicity.8, 9