Optically active seleninamides: isolation, absolute configuration, and racemization mechanism

Optically active seleninamides were obtained for the first time by chromatographic resolution on an optically active column. The absolute configurations of the optically active seleninamides were determined by comparing their chiroptical properties with those of analogous sulfinamides, the stereochemistry of which was determined by transformation into chiral sulfoxides of known configurations. The optically active seleninamides were found to racemize in solution. Kinetic studies of the racemization and theoretical studies clarified that the racemization of the optically active seleninamides in solution proceeds via hypervalent hydrates formed by the reaction with water.     

Stereocontrolled total synthesis of potent immunosuppressant FR901483

A total synthesis of the potent immunosuppressant FR901483 (1) has been accomplished. The key feature of our convergent synthesis is the stereoselective incorporation of the p-methoxybenzyl and methylamino groups within the core moiety 10. Tricycle 10 was itself constructed by an intramolecular aldol reaction of the symmetrical keto-aldehyde 7. [Structure: see text]     

Protein separation with surfactant-coated polystyrene involving Cibacron Blue 3GA-conjugated triton X-100

Through mixing of porous polystyrene particles (Amberlite XAD-4), non-ionic surfactants, and surfactant-conjugated substrates (affinity ligand) in an aqueous solution led to the formation of a novel medium (affinity admicelle) for protein separation. The ligand (CB-Triton) was synthesized by mixing a triazine dye (Cibacron Blue 3GA (CB)) and a polyoxyethylene-type non-ionic surfactant (Triton X-100) in weakly alkaline solutions. Triton X-100 and CB-Triton were competitively sorbed onto XAD-4. Albumin (bovine serum), alcohol dehydrogenase (yeast), and lysozyme (chicken egg) having specific interaction to CB were collected onto the affinity admicelle. On the other hand, the collection of ovalubmin (chicken egg white), having no binding ability to CB, was negligibly small. Lysozyme in 100 microl of chicken egg white, diluted with 900 microl of 10 mM Tris-HCl (pH 7.4), was successfully collected on 18 mg of CB-Triton admicelles and, then, it was eluted with 1 ml of aqueous solution of 100 mM phosphate (pH 7.4). The recovery based on the activity for the lysis of micrococcus and the concentration factor were 60% and 40 (n = 3), respectively.     

Cytotoxic alkaloids and a flavan from the bulbs of Crinum asiaticum var. japonicum

A new pyrrolophenanthridone alkaloid, criasiaticidine A (1), was isolated from the bulbs of Crinum asiaticum var. japonicum, together with pratorimine (2), lycorine (3) and 4'-hydroxy-7-methoxyflavan (4). The structure of the new alkaloid was determined to be 4,5-etheno-9,10-dihydroxy-6-phenanthridone by spectroscopic means. The cytotoxicity of the isolated compounds 1-4 was evaluated in vitro against Meth-A (mouse sarcoma) and Lewis lung carcinoma (mouse lung carcinoma) tumor cell lines. Furthermore, 3 was examined for in vivo antitumor activity with LLC tumor cells.     

Intramolecular cycloaddition of O-tert-butyldimethylsilyloximes in the presence of BF3 x OEt2

[reaction: see text] Intramolecular cycloaddition of novel 1,3-dipoles, N-boranonitrones, was examined. Treatment of O-tert-butyldimethylsilyloximes 9-12 having olefin moieties with 2 equiv of BF3 x OEt2 generated N-boranonitrones, which underwent intramolecular cycloaddition to afford N-nonsubstituted cycloadducts 16 (and/or 18) after extractive workup. Despite the Lewis-acidic conditions, the olefin geometry of the substrates was retained in the cycloadducts in the present cycloaddition. The electronic nature of the N-boranonitrones appeared to be electrophilic. In the case of substrate 11c, having an electron-donating methyl group at an internal position of the olefin moiety, the cycloaddition gave the bridged cycloadduct 18b. The cycloaddition proceeded at relatively low temperature, and the diastereoselectivity was high.     

Himeradine A,a novel C27N3-type alkaloid from Lycopodium chinense

A novel C(27)N(3)-type Lycopodium alkaloid consisting of a fastigiatine-type skeleton (C(16)N(2)) and a quinolizidine moiety (C(11)N), himeradine A (1), has been isolated from the club moss Lycopodium chinense, and the structure and relative stereochemistry were elucidated on the basis of spectroscopic data.     

Phosphoramidites are efficient,green organocatalysts for the Michael reaction. Mechanistic insights into the phosphorus-catalyzed Michael reaction of alkynones and implications for asymmetric catalysis

Hexamethylphosphorous triamide (HMPT) and other phosphoramidites and phosphites have been found to be efficient catalysts for the Michael reaction of alkenones and alkynones with malonates, alpha-cyano esters, beta-keto esters, and nitro compounds. The relatively nontoxic, easily hydrolyzed HMPT catalyzes the Michael reaction within seconds at room temperature in the absence of a solvent, and the reaction is worked up simply by removing the catalyst in vacuo. The Michael reactions of alkynones, unlike those of alkenones, are shown to be irreversible. The implications for asymmetric catalysis are discussed.     

Racemic [1SR,2RS,(RS)]-N-cyano(phenyl)methyl-1-aminoindan-2-ol: crystal structure and reactivity towards thermal epimerization in the solid state

A diastereomeric mixture of racemic α-amino nitriles [1SR,2RS,(SR)]- (1) and [1SR,2RS,(RS)]-N-cyano(phenyl)methyl-1-aminoindan-2-ol (2) was thermally epimerized in the solid state to give diastereopure [1SR,2RS,(SR)]-1. The reaction was about 26 times slower than the same reaction of a mixture of their enantiopure counterparts, showing that different mechanisms operated between the two transformations. X-ray crystallographic analysis revealed that in the former transformation, racemic-compound crystals of 2 were converted into conglomerate crystals of 1, while in the latter, enantiomeric crystals of 2 were converted into enantiomeric crystals of 1. The difference in the reactivity toward the epimerization between the racemic and the enantiopure mixture could be rationalized by the difference in the stability of compound 2 in the two crystal forms.     

Colouring mechanism of dyed KDP crystal by quantum chemistry

Dye adsorption mechanism, in particular, colouring mechanism of KDP (KH₂PO₄) crystal was investigated by quantum chemistry in this study. Phenomena, such as different preferentially coloured faces of KDP when co-crystallised with different dyes, are explained by the minimum and maximum values of electrostatic potential (ESP). Furthermore, it is found that the ESP distribution of a dye molecule may not necessarily be the single mechanism affecting the dye adsorption in a crystal structure; and that the degree of protonation, crystal surface condition, steric exclusion of dye and the orientation of dye molecules situating on the crystal surface may as well be important factors for the dye adsorption.     

Sensitive determination of phenothiazines in body fluids by gas chromatography with surface ionization detection.

Fourteen phenothiazine derivatives were tested for their detection by gas chromatography (GC) with surface ionization detection (SID). The sensitivity of GC-SID was highest with trimeprazine and levomepromazine, which contain aliphatic tertiary amino side chains, and lowest with thiethylperazine and thioproperazine, which contain sulphur residues. Chlorpromazine, trimeprazine and promazine showed excellent linearity between the SID response and the drug amount in the range 0.25-3.0 pmol on-column. Their detection limits were as low as ca. 5-10 pg (15-30 fmol) on-column (250-500 pg per ml of body fluid). A detailed procedure for isolation of phenothiazines from human whole blood and urine using Sep-Pak C18 cartridges, before the GC with SID, is also presented. The recoveries of the drugs (100 pmol), which were added to 1 ml of whole blood or urine, were more than 79%. The baselines remained steady as the column temperature was increased.