Aurilide, a cytotoxic depsipeptide from the sea hare Dolabella auricularia: isolation, structure determination, synthesis, and biological activity

The bioassay-guided fractionation of the cytotoxic constituents of the Japanese sea hare Dollabella auricularia led to the isolation of aurilide (1), a 26-membered cyclodepsipeptide. The gross structure of 1 was established by spectroscopic analysis including 2D NMR techniques. The absolute stereostructure was determined by chiral HPLC analysis of acid hydrolysates of 1 and by the enantioselective synthesis of a degradation product arising from a dihydroxylated fatty acid portion. The enantioselective synthesis of 1 was achieved in 12% overall yield (16 steps) and confirmed the absolute stereostructure of 1. The cytotoxicity of 1 was evaluated using a synthetic sample, which was found to exhibit potent cytotoxicity against HeLa S₃ cells with an IC₅₀ of 0.011 μg/mL. Further biological and pharmacological studies of 1 have been carried out by using synthetic 1.     

Diastereoselective inter- and intramolecular pinacol coupling of aldehydes promoted by monomeric titanocene(II) complex Cp(2)TiPh

A monomeric titanocene(III) derivative, Cp(2)TiPh, effectively promoted the pinacol coupling of both an aromatic aldehyde, benzaldehyde, and an aliphatic aldehyde, 3-phenylpropionaldehyde. The same reactive complex was successfully generated by a catalytic amount of a precursor, Cp(2)Ti(Ph)Cl, and its stoichiometric amount of Zn. The Cp(2)TiPh-catalyzed pinacol coupling of benzaldehyde derivatives and aliphatic aldehydes afforded the corresponding 1,2-diols in high yields with moderate to good threo-selectivity. On the other hand, Cp(2)TiPh-catalyzed pinacol cyclization of dials gave cyclic 1,2-diols with excellent diastereoselectivity. The extension of this protocol to chiral dials demonstrated that the phenyltitanium complex catalytically transmitted an axial chirality or a central chirality of the starting dials to the central chirality of the resultant 1,2-diols.     

PICOSECOND LASER PHOTOLYSIS STUDIES OF FLUORESCENCE QUENCHING MECHANISMS OF FLAVIN: A DIRECT OBSERVATION OF INDOLE-FLAVIN SINGLET CHARGE TRANSFER STATE FORMATION IN SOLUTIONS and FLAVOENZYMES

Formation of singlet charge transfer (heteroexcimer) states in the course of the fluorescence quenching of lumiflavin and riboflavin tetrabutyrate by indole and N-methylindole have been directly observed by means of time-resolved absorption spectral measurements using a picosecond laser photolysis method. Similar transient spectra have been observed also in the case of a flavoenzyme, D-amino acid oxidase.     

Structures of Ganoderic Acid A and B,Two New Lanostane Type Bitter Triterpenes from Ganoderma lucidum (FR.) KARST.

The structures of two new bitter triterpenes, ganoderic acid A and B. isolated from a mushroom Ganoderma lucidum (FR.) Karst. (Polyporaceae) were determined as 1 and 2 on the basis of spectral data. Ganoderic acid A is a novel highly oxidized triterpene bearing a boat-shaped A-ring of lanostane.     

Synthesis of block copolymer with polystyrene and nylon units

Bis-ε-aminocaproylaminocaproylhexamethylenediamine ( I ) was synthesized as an analog of 6-nylon pentamer diamine, and its incorporation into block copolymers was studied with the use of α,ω-dihydroxyl, α,ω-bisdimethylchlorosilyl, and α,ω-diepoxy polystyrene. In the course of the experiments, the stability and the reactivity of 4,4′-diphenylmethane diisocyanate and tetramethylene diisocyanate in aprotic dipolar solvents were examined by infrared spectroscopy. The only usable solvent, N-methylpyrrolidone, was found still inadequate for the synthesis involving I, diisocyanate, and α,ω-dihydroxyl polystyrene. A block copolymer having M _n = 18,000 was obtained by the reaction of I and α,ω-diepoxy polystyrene. All T_g values of the block copolymers were above 90°C, higher than for polystyrenes with corresponding molecular weight.     

Reaction of tetraazathiapentalene and thiadiazolopyrimidine derivatives with heterocumulenes: Cycloaddition and elimination reactions via hypervalent sulfur intermediates

Tetraazathiapentalene derivative 1 reacts with heterocumulenes such as diphenylketene (2) and 2‐pyridylisothiocyanate (5) to give heterocycles 3, 6 and 7 with elimination of methylisothiocyanate. The reactions of thiadiazolopyrimidine derivatives 8a‐b with ethoxycarbonyl isothiocyanate (9) and carbon disulfide (11) gives heterocycles 10 and 12 via thermal decomposition of 1:1 cycloadducts C and D which have a hypervalent sulfur. The mechanistic and reactivity features of these reactions are described.     

Effect of monomer concentration on characteristics of methacrylic acid-grafted polyethylene film prepared by photografting

The effect of monomer concentration on photografting of methacrylic acid (MAA) onto linear low-density polyethylene (PE) film (thickness=30 μm) was investigated at 60 °C in water solvent together with the location of MAA-grafted chains. Xanthone was used as a photoinitiator which was coated on the film sample earlier. The higher percentage of grafting and graft efficiency were afforded for the system with the higher monomer concentration. The resultant MAA-grafted films were subjected to measurements of pH-responsive character and ability to adsorb cupric ion in order to understand the characteristics of function introduced. The grafted samples exhibited the pH-responsive character, where they shrank and swelled in acidic and alkaline media, respectively. The pH-responsive character of the grafted films was higher for the samples prepared in the system with a higher monomer concentration. Moreover, the grafted samples exhibited the ability to adsorb cupric ion, and the ability was reduced when the sample was prepared in the system with a higher monomer concentration. The different extents of the pH-responsive character and ability to adsorb cupric ion of the resulting grafted PE films were discussed in terms of location of grafted chains in the film substrate, which was determined by a scanning electron microscope and an attenuated total reflection infrared spectroscopy.     

Absolute stereochemistry of amphidinolide C

[structure in text] The absolute configurations at 12 chiral centers in amphidinolide C (1), a potent cytotoxic 25-membered macrolide isolated from a marine dinoflagellate Amphidinium sp., were determined to be 3S, 4R, 6R, 7R, 8R, 12R, 13S, 16S, 20R, 23R, 24R, and 29S by combination of NMR analyses, degradation experiments, and synthesis of the C-1-C-7 segment.     

A new synthetic method: Direct replacement of the nitro group by hydrogen or deuterium

The nitro group in tertiary or secondary aliphatic nitro compounds is replaced by hydrogen or deuterium on treatment with tributyltin hydride or tributyltin deuteride, respectively.     

Photodegradation of polyethylene in the presence of ferric salt: Influence of ferric acetylacetonate on model compounds

The influence of ferric acetylacetonate [Fe(acac)₃] on the photodegradation of model compounds of polyethylene (PE) was examined. By studying electron-spin-resonance (ESR) spectra of photoirradiated compounds such as 1-octene and 1,7-octadiene, which contain carbon double bonds, Fe(acac)₃ was found to accelerate the formation of allyl radical by contact with them. On the other hand, Fe(acac)₃ suppressed the radical formation based on Norrish type I reaction in a carbonyl group of compounds such as 2-octanone and 3-octanone. Based on the study of ultraviolet (UV) spectra as well as ESR spectra on photoirradiated samples, the influence of Fe(acac)₃ on the photodecomposition of model compounds of PE was discussed. Finally, the discussion turned to the mechanism of photodecomposition of PE in the presence of ferric salt.