High performance liquid chromatography equipped with a cathodic detector and column-switching device as a high-throughput method for a phosphatase assay with p-nitrophenyl phosphate

A preparative high-speed counter-current chromatography (HSCCC) method for isolation and purification of coumarin compounds from the Chinese medicinal plant Peucedanum decursivum (Miq.) Maxim (Zihuaqianhu in Chinese) was successfully established by using light petroleum-ethyl acetate-methanol-water (5:5:7:4, v/v) as the two-phase solvent system. The upper phase of light petroleum-ethyl acetate-methanol-water (5:5:7:4, v/v) was used as the stationary phase of HSCCC. Nodakenetin (2.8 mg), 6.1 mg of Pd-C-IV, 7.3 mg of Pd-D-V, 4.7 mg of ostruthin, 7.8 mg of decursidin and 11.2 mg of decursitin C with the purity of 88.3%, 98.0%, 94.2%, 97.1%, 97.8% and 98.4%, respectively, were separated successfully in one-step separation from 150 mg of crude sample from P. decursivum (Miq.) Maxim. After purified by HSCCC again with light petroleum-ethyl acetate-methanol-water (5:5:4:5, v/v) as the two-phase solvent system, the purity of (I) can reach 99.4%. The structures of all the compounds were identified by 1H NMR and 13C NMR.     

General synthesis of sugar-pendant 1,3-propanediamines containing a C-glycoside linkage

A straightforward route to C-glycoside linked sugar-pendant 1,3-propanediamines is described. The three-step preparation procedure involves (1) C-glycosylation of an OH-protected α-glycosyl halide with malononitrile, (2) catalytic hydrogenation of the nitriles to amines, and (3) deprotection of acetyl groups via acid-catalyzed hydrolysis. In the case of the galactose derivative, excess sodiomalononitrile promotes the second addition of a carbanion in the first step. The β-anomeric configuration was confirmed by X-ray crystallography of the glycosylated intermediates. This method demonstrates a general method to access a new class of carbohydrate-pendant C-glycoside chelators.     

Synthesis of Optically Active Vasicinone Based on Intramolecular Aza-Wittig Reaction and Asymmetric Oxidation(1)

Both optical isomers of a quinazoline alkaloid, vasicinone, were synthesized by two different methods. The first method used (3S)-3-hydroxy-gamma-lactam as a chiral synthon, which was, after O-TBDMS protection, o-azidobenzoylated followed by treatment with tri-n-butylphosphine to afford (S)-(-)-vasicinone via the tandem Staudinger/intramolecualr aza-Wittig reaction. The second method utilized asymmetric oxygenation of deoxyvasicinone with (1S)-(+)- or (1R)-(-)-(10-camphorsulfonyl)oxaziridine (the Davis reagent), respectively. The aza-enolate anion of deoxyvasicinone was treated with (S)-(+)-reagent to afford (R)-(+)-vasicinone in 71% ee, while the reaction with (R)-(-)-reagent gave (S)-(-)-vasicinone in 62% ee. The optical purity was analyzed by HPLC on specially modified cellulose as a stationary phase. These results provided a facile method to prepare both optical isomers of vasicinone and confirmed the recently reversed stereochemistry of natural (-)-vasicinone.     

Effects of ligands on the “living” radical polymerization initiated by the aged Cr2+ plus benzoyl peroxide system

The “living” radical polymerization of methyl methacrylate with the aged Cr²⁺ plus benzoyl peroxide (BPO) system in the presence of various amines as ligand has been studied in N,N′-dimethylformamide. Aliphatic amines such as ethylenediamine diminished the rate of polymerization, while dipyridyl (dipy) and o-phenanthroline (phen) accelerated the polymerization rate as follows: phen > dipy > pyridine ? none. Specifically, the rate of polymerization in the presence of phen had a maximum value at [phen]/[Cr²⁺] = 0.5. The retardation of polymerization by aliphatic amines was explained by the interaction of BPO with free and coordinated amines. The latter result may support the mechanism involving the complexed radical proposed for the living radical polymerization with the aged Cr²⁺ + BPO system. In the presence of phen the effects of aging period and aging temperature as well as polymerization temperature were studied and the nature of complexed radicals is discussed.     

Product-retardation and -activation of catalytic hydrolysis by phospholipase D in small unilamellar vesicles of egg yolk phosphatidylcholine

 We evaluated the hydrolysis of egg yolk phosphatidylcholine (PC) by phospholipase D from Streptomyces chromofuscus (PLD) in small unilamellar vesicles (SUV) in presence of 50 μM Ca²⁺. After initial choline production (hydrolysis of 1.5% of the PC at the outer leaflets of the vesicle bilayers), the hydrolysis was reduced to 5% of the initial velocity. The kinetic behavior in SUV of premixed PC and a low percentage of the hydrolysis product, phosphatidic acid (PA), was similar to that of PC SUV. The reduced velocity disappeared when the membrane structure was disintegrated by means of a nonionic surfactant. In the retardation phase, the partially hydrolyzed vesicles (postsubstrates) had much higher affinity for PLD than fresh PC SUV. These results indicated that small clusters of the product, PA, at the vesicle surface were responsible for the reduced velocity of hydrolysis. The initial velocity increased in a biphasic manner with the substrate concentration. At a PC concentration range up to 4 mM, the experimental data fit Michaelis–Menten kinetics. At concentrations above 6 mM, the velocity again markedly increased. Negatively charged mixed vesicles of PC and PA did not have such kinetics. Furthermore, adding PC SUV to the postsubstrates, where the fraction of free PLD was less than 0.05, induced steep choline production. These results showed that PLD bound to vesicles had higher activity than free PLD. We speculated that PLD bound to vesicles collided with and was directly transferred to PC SUV when the fraction of free PLD in aqueous medium was very small. Received: 5 November 1996 Accepted: 26 February 1997     

Preferential CO oxidation promoted by the presence of H2 over K-Pt/Al2O3

In preferential CO oxidation in H2-rich gas, K-Pt/Al2O3(K/Pt = 10) was very effective in decreasing CO concentration below 10 ppm in the 375-410 K range, and the turnover frequency of the K-Pt/Al2O3 was 20 times as high as that of Pt/Al2O3 at 353 K; furthermore, the activity of CO oxidation was promoted drastically by the presence of H2.     

Novel carbohydrate-appended metal complexes for potential use in molecular imaging

Seven discrete sugar-pendant diamines were complexed to the {M(CO)(3)}(+) ((99m)Tc/Re) core: 1,3-diamino-2-propyl beta-D-glucopyranoside (L(1)), 1,3-diamino-2-propyl beta-D-xylopyranoside (L(2)), 1,3-diamino-2-propyl alpha-D-mannopyranoside (L(3)), 1,3-diamino-2-propyl alpha-D-galactopyranoside (L(4)), 1,3-diamino-2-propyl beta-D-galactopyranoside (L(5)), 1,3-diamino-2-propyl beta-(alpha-D-glucopyranosyl-(1,4)-D-glucopyranoside) (L(6)), and bis(aminomethyl)bis[(beta-D-glucopyranosyloxy)methyl]methane (L(7)). The Re complexes [Re(L(1)-L(7))(Br)(CO)(3)] were characterized by (1)H and (13)C 1D/2D NMR spectroscopy which confirmed the pendant nature of the carbohydrate moieties in solution. Additional characterization was provided by IR spectroscopy, elemental analysis, and mass spectrometry. Two analogues, [Re(L(2))(CO)(3)Br] and [Re(L(3))(CO)(3)Br], were characterized in the solid state by X-ray crystallography and represent the first reported structures of Re organometallic carbohydrate compounds. Conductivity measurements in H(2)O established that the complexes exist as [Re(L(1)-L(7))(H(2)O)(CO)(3)]Br in aqueous conditions. Radiolabelling of L(1)-L(7) with [(99m)Tc(H(2)O)(3)(CO)(3)](+) afforded in high yield compounds of identical character to the Re analogues. The radiolabelled compounds were determined to exhibit high in vitro stability towards ligand exchange in the presence of an excess of either cysteine or histidine over a 24 h period.     

Novel synthesis of carbapenam by intramolecular attack of lactam nitrogen toward eta1-allenyl and eta3-propargylpalladium complex

When a THF solution of beta-lactam having propargyl phosphate was warmed in the presence of 5 mol % of Pd(2)(dba)(3) x CHCl(3), 20 mol % of a bidentate ligand, and sodium acetate (1.5 equiv) at 40 degrees C for 22 h, carbapenam was produced in high yield. In this reaction, the lactam nitrogen attacked the central carbon of a eta(3)-propargylpalladium complex, which was formed from propargyl phosphate and Pd(0).     

From penicillin to penem and carbapenem. VI1) : Synthesis of dethiathienamycin

A new C₃-unit substitution reaction at C-4 position of 4- acetoxyazetidinone derivative ($\text{1}$ and $\text{5}$) by tetraallyltin ($\text{2}$) in the presence of 1/10 eq. of BF₃-ether in methylene chloride is described. From 4-allylazetidinone derivative ($\text{3}$) via ylid intermediate ($\text{14}$) dethiathienamycin ($\text{16}$) was synthesized.     

Completely stereocontrolled synthesis of the right fragment of salinomycin,a polyether antibiotic,by means of the chelation-controlled grignard reaction

In the course of our synthetic study of salinomycin ($\text{1}$), an ionophorous polyether antibiotic, the γ-lactone ($\text{2}$) corresponding to the C-21～C-30 fragment (the right fragment) of $\text{1}$ was synthesized from D-mannitol and ethyl L-lactate as chiral starting materials. The complete stereocontrol for the construction of new chiral centers has been achieved by means of the chelation-controlled Grignard reaction and the tetrahydropyran synthesis via the acid catalyzed epoxide ring opening.