Synthesis of Optically Pure Norcantharidin Analogue NCA‐01, a Highly Selective Protein Phosphatase 2B Inhibitor,and its Derivatives

An efficient synthetic route to optically pure norcantharidin analogue NCA‐01, a highly selective inhibitor of protein phosphatase 2B (PP2B; calcineurin), has been developed. The absolute stereochemistry of the enantiomers was determined by X‐ray crystallographic analysis. Optically pure NCA derivatives that had various substituents at the C1 position were synthesized in a similar manner. The PP2B‐inhibitory activities of NCA‐01 and its derivatives were independent of the enantiomeric form. NCA‐01 dimethyl ester potently inhibited IL‐2 production in Jurkat cells.     

Aggregation of 1-dodecyl-3-methylimidazolium nitrate in water and benzene studied by SANS and 1H NMR

Aggregation of imidazolium-based ionic liquid, C(12)mim(+)NO(3)(-), in both polar solvent of water and nonpolar solvent of benzene was elucidated by electrical conductivity, small-angle neutron scattering (SANS), and (1)H NMR measurements. The electrical conductivities of C(12)mim(+)NO(3)(-)-water solutions at 298 K as a function of ionic liquid concentration showed a break point at 8.4 mmol dm(-3) as a cmc. However, those of C(12)mim(+)NO(3)(-)-benzene solutions drastically increase in accordance with a cubic function of concentration, but without a break point. The SANS profiles of both aqueous and benzene solutions obviously differ from each other. The profiles of the aqueous solutions indicated the formation of polydisperse spherical micelles. Those of the benzene solutions revealed Ornstein-Zernike behavior. Thus, C(12)mim(+)NO(3)(-) forms clusters in the benzene solutions, but the shape of clusters is indefinite. On the basis of the (1)H NMR chemical shifts of the aqueous solutions, the effect of nitrate on the formation of micelles was discussed on a microscopic scale. Furthermore, the interactions among C(12)mim(+), NO(3)(-), and benzene molecules in the benzene solutions were considered according to the (1)H NMR data.     

Platinum‐Catalyzed Friedel–Crafts‐Type C−H Coupling–Allylic Amination Cascade to Synthesize 3,4‐Fused Tricyclic Indoles

A novel platinum‐catalyzed cascade cyclization reaction was developed by intramolecular Friedel–Crafts‐type C?H coupling of aniline derivatives with a propargyl carbonate unit‐allylic amination sequence. Treatment of various propargyl carbonates tethered to meta‐aniline derivatives with a Pt(dba)₃/DPEphos catalyst system afforded the corresponding 3,4‐fused tricyclic 3‐alkylidene indolines in 42–99 % yield, which were transformed into 3,4‐fused indole derivatives by reaction with trifluoroacetic acid. The reaction products exhibited antiproliferative activities against cancer cells, but not normal cells, revealing the potential usefulness of this reaction for medicinal chemistry.     

Total syntheses of chaetocin and ent-chaetocin

The first total synthesis of chaetocin (1), a potent histone methyltransferase inhibitor, is described in detail. Key reactions were radical bromination for α-oxidation of the diketopiperazine ring, and reductive radical coupling for construction of the dimeric core structure. Stereoselective construction of the disulfide bridges was achieved via substitution reaction with H₂S. The total synthesis of 1 was accomplished in nine steps starting from known d-amino acid derivatives. Total synthesis of non-natural ent-chaetocin (ent-1) was also achieved via the established synthetic route, starting from l-amino acid derivatives.     

New approach for two chromene carboxylic acids having a fully substituted benzene ring

Two chromene carboxylic acids having a fully substituted benzene ring, 8-chlorocannabiorcichromenic acid (1) and mycochromenic acid (2), were synthesized via thermal cyclization of the corresponding four substituted phenyl propargyl ethers.     

Symbioimine exhibiting inhibitory effect of osteoclast differentiation, from the symbiotic marine dinoflagellate Symbiodinium sp

An amphoteric iminium metabolite, symbioimine (1), was isolated from a cultivated symbiotic marine dinoflagellate Symbiodinium sp. Its structure was deduced by spectroscopic analysis and X-ray crystallographic analysis. Symbioimine (1) has a characteristic 6,6,6-tricyclic iminium ring structure and an aryl sulfate moiety. The plausible biogenetic pathway of 1 can be explained by an intramolecular Diels-Alder reaction followed by imine cyclization. Symbioimine (1) inhibited the differentiation of RAW264 cells into osteoclasts, whereas its cell viability was not affected. Thus, symbioimine (1) is an antiresorptive drug candidate for the prevention and treatment of osteoporosis in postmenopausal women.     

Electrooxidation of alcohols using a new double mediatory system

The electrochemical oxidation of alcohols was accomplished by using a double mediatory system in which both alkyl methyl sulfide and bromide act in concert as mediators.     

An efficient enantioselective fluorination of various beta-ketoesters catalyzed by chiral palladium complexes

Reflecting the importance of fluorinated organic compounds in medicinal chemistry, development of an efficient method for catalytic enantioselective fluorination is increasingly desirable. Using a novel palladium complex 2 (1-2.5 mol %), various beta-ketoesters including cyclic and acyclic substrates were fluorinated with excellent enantioselectivity in the range of 83-94% ee. It is environmentally advantageous that this reaction proceeds well in solvents such as EtOH, rather than usual organic solvents. Furthermore, the product was successfully tranformed into both alpha-fluoro beta-hydroxy and beta-amino acid derivatives, which should be extremely useful in developing novel drugs.     

A facile preparation of 4-(1-Acetyl-4(1H)-pyridylidene)-2-oxazohn-5-ones

4-(1-Acetyl-4(1H)-pyridylidene)-2-oxazolin-5-ones were prepared by the reaction of acylglycines with pyridine and acetic anhydride under oxygen. Acidic and alkaline hydrolysis of 2-oxazolin-5-ones provided oxazole derivatives, pyridine derivatives, and carboxylic acids.