Published papers

Africane-type sesquiterpenoids consist of a bicyclo[5.3.0]decane structure and have been isolated from various natural environments. Their characteristic C–C bond motifs, including a seven-membered ring core, fascinate many synthetic organic chemists. Thirteen total syntheses have been reported over the past four decades. The purpose of this digest is to provide an overview of these total syntheses of africane-type sesquiterpenoids, with an emphasis on methods for constructing the seven-membered ring structure.

Africane-type sesquiterpenoids are a unique tricyclic carbon architecture sesquiterpenoid isolated as natural products. Δ9(15) -africanene has been reported to exhibit anti-inflammatory activity for carrageenan-induced rat foot edema. In this study, we reported structure–activity relationship study of africane-type sesquiterpenoids and found that some africane-type sesquiterpenoid analogs and their synthetic intermediate showed potent anti-inflammatory activity. To identify the mode of action of africane-type sesquiterpenoids and their synthetic intermediate, we evaluated the anti-inflammatory activity using lipopolysaccharide (LPS)-stimulated mouse macrophage RAW264.7 cells. Treatment with the africane-type compounds and their synthetic intermediate suppressed LPS-induced expressions of Cox-2 protein and mRNAs of the inflammatory cytokines IL-1β and IL-6 at the concentrations that did not affect cell viability. Interestingly, although these africane-type compounds and their synthetic intermediate suppressed the pro-inflammatory cytokines’ expressions, the compounds did not modulate NF-κB activation. These results suggest that the africane-type compounds and their synthetic intermediate are anti-inflammatory compounds that suppress the expression of LPS-induced inflammatory mediators independently of NF-κB activation.

Coenzyme A (CoA) is a well-known cofactor that plays an essential role in many metabolic reactions in all organisms. In Plasmodium falciparum, the most deadly among Plasmodium species that cause malaria, CoA and its biosynthetic pathway have been proven to be indispensable. The first and rate-limiting reaction in the CoA biosynthetic pathway is catalyzed by two putative pantothenate kinases (PfPanK1 and 2) in this parasite. Here we produced, purified, and biochemically characterized recombinant PfPanK1 for the first time. PfPanK1 showed activity using pantetheine besides pantothenate, as the primary substrate, indicating that CoA biosynthesis in the blood stage of P. falciparum can bypass pantothenate. We further developed a robust and reliable screening system to identify inhibitors using recombinant PfPanK1 and identified four PfPanK inhibitors from natural compounds.

The orange leafhopper, Cicadulina bipunctata (Melichar) (Hemiptera: Cicadellidae), is an insect pest of various Poaceae plants. Feeding by this leafhopper species induces growth suppression and gall formation, which is characterized by severe swelling of leaf veins, named wallaby ear symptoms. In this study, we performed histological analysis of the cell differentiation in the galled leaves of rice seedlings and devised a new method to quantify the degree of gall formation. In the histological study, abnormal vascular cell patterning and differentiation were observed in the galled leaves. Morphological changes during gall formation were quantitatively evaluated through image analysis.

Unlike our previous study that identified D-myo-inositol 4,5-bisphosphate (Ins(4,5)P2, 1) from ostrich eggshell, the compound myo-inositol 1,4,5,6-tetrakisphosphate (Ins(1,4,5,6)P4, 2) was isolated as an almost racemic mixture from the internal region of chicken eggshell. Furthermore, 2, 2-[2H]-2, and amorphous CaCO3 were prepared as tools for assessment about transformation of CaCO3 during bone formation.

Orange leafhopper Cicadulina bipunctata feeding induces wallaby ear symptoms, namely growth suppression and gall formation characterized by severe swelling of leaf veins, on various Poaceae, thereby leading to low crop yields. Here, we investigated the development of wallaby ear symptoms on rice seedlings due to C. bipunctata feeding. After confirming that C. bipunctata feeding induces growth suppression and gall formation on rice seedlings, we further demonstrated that gall formation score decreased with decreasing levels of nitrogen in the medium and that C. bipunctata feeding induces the expression levels of nitrogen transporter genes. These gene expression changes may participate in the nutrient accumulation observed in galled tissues and in gall formation. In addition, these expression changes should induce growth promotion but the inhibition of gibberellin signaling by C. bipunctata feeding might be the reason why growth is suppressed. Treatment with plant growth regulators did not affect gall formation, suggesting the existence of a complex gall formation mechanism by C. bipunctata feeding.

Practical total syntheses of africane-type sesquiterpenoids were realized by reexamination of a divergent strategy employing optimized three-component coupling followed by ring-closing metathesis and substrate-controlled cyclopropanation. This sequential eight-step conversion provided Δ9(15)-africanene, a common bicyclo[5.3.0]decane intermediate for the syntheses of africane derivatives, in more than twice the yield as in the previous approach. The scalability and robustness of this improved synthetic route were confirmed by gram-scale preparation of Δ9(15)-africanene. In vitro cell-based assays of the synthesized africane-type sesquiterpenoids disclosed that ester-incorporating derivatives showed cytotoxic activity against HeLa cells. The effect of relative and absolute configuration of africane-9,15-diol monoacetates on the cytotoxicity against HeLa cells was also investigated.

Calcium carbonate in avian eggshell is used as a calcium source for bone formation during embryonic development. We studied ostrich eggshells as a representative avian egg and found that the calcium reserve assembly (CRA) region, eventually dissolving for bone formation, consists of nano-granules comprising amorphous calcium carbonate (ACC) by careful microscopic observation. ACC is unstable phase of calcium carbonate with high solubility and is stabilized by additives. As such a stabilizer, we found small molecules from eggshell internal region. Particularly, the ACC was recreated by the formation of calcium carbonate in the presence of D-myo-inositol 4,5-bisphosphate (Ins(4,5)P2), isolated from ostrich eggshell for the first time in this study. Further mass spectrometric imaging technique revealed that Ins(4,5)P2 is localized at the CRA region, suggesting that this compound could play a major role that makes it easier to dissolve and internalize eggshell calcium during embryogenesis.

Hydrazine-embedded unsubstituted butterfly-shaped biphenothiazine and its sulfoxides were synthesized by dimerization of 1,9-dibromophenothiazine, which was prepared by realizing selective debromination at the 3,7-positions of 1,3,7,9-tetrabromophenothiazine. cis/trans-Biphenothiazine sulfoxide was selectively prepared by changing the oxidation temperature to control the inversion rate of the butterfly shape of the intermediate. Their butterfly-shapes, conformations, photophysical properties (UV-vis absorption, fluorescence), and redox properties were elucidated by X-ray analysis, DFT calculations, spectral and electrochemical measurements. Fluorescent hydrazine-embedded biphenothiazine sulfoxides and bicarbazoles were applied to cell imaging of HeLa cells. The bicarbazoles exhibited high fluorescence signals in the cells with low toxicity.

The first total synthesis of pactalactam was accomplished using substrate-controlled stereoselective aziridination and regioselective aziridine ring-opening to construct three continuous amino groups on an octasubstituted cyclopentane core. The cyclopentane framework was obtained by ring-closing metathesis and aldol coupling using a l-threonine-derived oxazoline compound. Cyclic urea formation, m-acetylphenyl group introduction by Chan-Lam coupling, and primary alcohol-selective acylation yielded the reported pactalactam structure. The presence of pactalactam in the fermentation broth of pactamycin-producing bacteria was also confirmed.

カエンタケは近年中毒死亡事故を引き起こしている猛毒キノコである。このキノコの培養液より３種のmacrocyclic trichothecene類を単離した。また、子実体より、新規天然物3種を含む４種のmacrocyclic trichothecene類を単離、構造決定した。

青いキノコ、ロクショウグサレキン類の青色色素主成分はxylindeinである。Xylindeinの誘導体のX線結晶解析によりxylindeinの絶対立体配置を決定した。また、xylindein自体のX線結晶解析によりxylindeinの可能なatutomerのうち、これまでに提出されていた構造が正しいことを明らかにした。