Total synthesis of citridone A

The first total synthesis of citridone A has been achieved through regioselective intramolecular iodocyclization and regio- and stereoselective Pd(0)-catalyzed coupling as key reactions.     

Time-dependent fluctuations in infrared vsCH2 frequencies in acyl chain membranes of Acholeplasma laidlawii cells

We measured FT-IR spectra of intact Acholeplasma laidlawii cells grown at 37 °C on palmitic acid (C16:0) or on binary palmitic acid-d31/oleic acid (C16:0-d31/C18:1(9)) at an initial mole ratio of 2:3, which have been previously reported to produce significant fluctuations in CH₂ symmetric stretching (ν_sCH₂) and CD₂ asymmetric stretching (ν_aCD₂) frequencies (Biochim. Biophys. Acta 1279 (1996) 49). Time courses for acyl chain ν_sCH₂ and ν_aCD₂ frequencies determined from fourth derivative spectra are presented. Fluctuations were detected with the C16:0 enriched cells at temperatures above 40 °C as well as with the cells enriched in 2:3 C16:0-d₃₁/C18:1(9). These observations at temperatures above 40 °C for the C16:0 enriched cells were not in agreement with the conclusion in the previous work by Moore et al. Our results have suggested that the 2850 cm⁻¹ ν_sCH₂ band comprises two components arising from trans and gauche conformations, and that the fluctuations in ν_sCH₂ frequency are caused by random temporal changes in the relative intensities of these two components.     

A caffeine-sensitive membrane electrode: previous misleading report and present approach

Although a previous study [S.S.M. Hassan, M.A. Ahmed, M.M. Saoudi, Anal. Chem. 57 (1985) 1126] had shown that a caffeine-sensitive electrode made with picrylsulfonate and 1-octanol as a cation-exchanger and a solvent mediator, respectively, had a wide working pH range (5.5–9.5) and exhibited a Nernstian response, we could not find such response in this electrode. The present result was reasonable, because the pK_a value of caffeinium ion was reported to be around 0.7 and the neutral form of caffeine was predominant in the pH range examined. Thus, we reinvestigated the response characteristics of a caffeine electrode, taking into consideration the pK_a value, and constructed a new electrode with a combination of the lipophilic cation-exchanger, tetrakis[3,5-bis(2-methoxyhexafluoro-2-propyl)phenyl]borate (HFPB), and the solvent mediator with high degree of dielectric constant, 2-fluoro-2′-nitrodiphenyl ether (FNDPE). This electrode showed a pH-dependent response to caffeinium ion and gave a detection limit of 50 μM with a slope of 55 mV per concentration decade at pH 2. The use of other solvent mediators was less effective than that of FNDPE. The electrode was applied for the determination of caffeine in some central stimulants.     

Relative and absolute stereochemistry of quinadoline B, an inhibitor of lipid droplet synthesis in macrophages

New fungal metabolites, designated quinadolines A (1) and B (2), were isolated from culture broth of Aspergillus sp. FKI-1746, and their structures were elucidated by NMR spectroscopy. The complete relative and absolute stereochemistry of 2 was determined by X-ray crystallography and amino acid analysis using a chiral column. Quinadolines moderately inhibited lipid droplet synthesis in mouse macrophages.     

Asymmetric total synthesis of (+)-K01-0509 B: determination of absolute configuration

K01-0509 B is a novel natural product which contains a carbamoylated cyclic guanidine. Our asymmetric total synthesis features a Sharpless asymmetric epoxidation and a stereocontrolled construction of the cyclic guanidine via an asymmetric nitroaldol reaction, followed by intramolecular SN2 cyclization. These reactions allowed the cyclic guanidine and the adjacent hydroxy group to be assembled, facilitating the asymmetric total synthesis and determination of the absolute stereochemistry of K01-0509 B. [reaction: see text].     

Synthesis of bridged heteroaromatic compounds as reference standards for coal degradation products

The synthesis of 2-naphthyl 2′-dibenzothienyl ether, 1-(1′-naphthyl)-2-(4″-acridinyl)ethane and a series of naphthylethyldibenzothiophenes is reported.     

Total synthesis of borrelidin

The total synthesis of borrelidin has been achieved. The best feature of our synthetic route is macrocyclization at C11-C12 for the construction of an 18-membered ring after esterification between two segments. A detailed examination of the macrocyclization led us to the samarium(II) iodide-mediated intramolecular Reformatsky-type reaction as the most efficient synthetic approach. The two key segments were synthesized through regioselective methylation, directed hydrogenation, stereoselective Reformatsky-type reaction, and MgBr2.Et2O-mediated chelation-controlled allylation.     

Tensyuic acids, new antibiotics produced by Aspergillus niger FKI-2342

Six new alkylitaconic acids, designated tensyuic acids A to F, were isolated from the culture broth of Aspergillus niger FKI-2342 by solvent extraction, silica gel column chromatography and HPLC. Their structures were elucidated by spectroscopic analysis including UV, NMR, and MS. They are all alkylitaconic acid derivatives. Only tesyuic acid C showed moderate antimicrobial activity against Bacillus subtilis.     

Yaequinolones J1 and J2, novel insecticidal antibiotics from Penicillium sp. FKI-2140

[chemical reaction: see text]. Two novel insecticidal antibiotics with a p-methoxyphenylquinolinone skeleton fused with a pyran ring, yaequinolones J1 (1) and J2 (2), have been isolated from Penicillium sp. FKI-2140, and structures were elucidated by spectroscopic studies including various NMR experiments. The relative stereochemistries were assigned by NOE experiments. Yaequinolones J1 and J2 showed toxicity against Artemia salina (brine shrimp) with the MIC value of 6.25 microg/mL.