Resolution of N-Acyl Amino Acids with Optically Active Neutral Amino Acid Amides

A convenient method of chemical resolution of DL-N-acyl amino acids was described. The resolution by using salt of N-acyl derivatives with a certain simple base, especially L-leucin-amide, was discussed. A new agent, L-leucinamide, readily gave L-alanine, L-valine, L-leucine, L-phenylalanine, L-tryptophan and L-methionine from the corresponding DL-N-acyl derivatives. Resolution done with L-tyrosinamide and L-phenylaninamide gave products lower in yield and purity than those resolved with L-leucinamide as resolving agent.     

Preparation of Optically Active 2-Aminobutanoic Acid via Optical Resolution by Replacing Crystallization

An attempt was made to use a simple procedure to obtain (R)- and (S)-2-aminobutanoic acids [(R)- and (S)-1] which are non-proteinogenic α-amino acids and are useful as chiral reagents in asymmetric syntheses. Compound (RS)-1 p-toluenesulfonate [(RS)-2], which is known to exist as a conglomerate, was optically resolved by replacing crystallization with (R)- and (S)-methionine p-toluenesulfonate [(R)- and (S)-3] as optically active co-solutes. When (S)-3 was employed as the co-solute, (R)-2 was preferentially crystallized from a supersaturated solution of (RS)-2 in 1-propanol, as was (S)-2 in the presence of (R)-3. (R)- and (S)-2 recrystallized from 1-propanol were treated with triethylamine in methanol to give (R)- and (S)-1 in optically pure forms.     

Microbial Resolution of 2-Hydroxy-3-nitropropionic Acid for Synthesis of Optically Active Isoserine

The biocatalytic stereoselective hydrolysis of 2-hydroxy-3-nitropropionic acid esters was studied. Forty enzymes and three hundred microorganism strains were examined for their ability to hydrolyze ethyl 2-hydroxy-3-nitropropionic acid. Nocardia globerula IFO13150 gave n-butyl (R)-2-hydroxy-3-nitropropionate with a 92% enantiomeric excess (ee) and the corresponding carboxylic acid with a 92%ee, which was easily converted to (S)-isoserine, a useful β-amino acid.     

Synthesis and Antiviral Activity of Betulonic Acid Amides and Conjugates with Amino Acids

Betulonic acid amides with aliphatic and heterocyclic amines and with L-amino acids were synthesized by the acid chloride method. Betulonic acid amide and L-methionine derivatives of betulonic acid and its 3-oxime effectively inhibit the influenza A virus. Betulonic acid octadecylamide is active against the herpes simplex Type 1 virus. The conjugate of betulonic acid 3-oxime with L-methionine is also active toward HIV-1. The tested compounds mainly show no activity toward the ECHO6 virus, which is devoid of a coat.     

Kinetics of Neutral Amino Acid Transport Across the Blood-Brain Barrier

Neutral amino acid (NAA) transport across the blood-brain barrier was examined in pentobarbital-anesthetized rats with an in situ brain perfusion technique. Fourteen of 16 plasma NAAs showed measurable affinity for the cerebrovascular NAA transport system. Values of the transport constants (Vmax, Km, KD) were determined for seven large NAAs from saturation studies, whereas Km values for five small NAAs were estimated from inhibition studies. These data, together with our previous work, provide a complete set of constants for prediction of NAA influx from plasma. Among the NAAs, Vmax varied at least fivefold and Km varied approximately 700 fold. The apparent affinity (1/Km) of each NAA was related linearly (r = 0.910) to the octanol/water partition coefficient, a measure of NAA side-chain hydrophobicity. Predicted influx values from transport constants and average plasma concentrations agree well with values measured using plasma perfusate. These results provide accurate new estimates of the kinetic constants that determine NAA transport across the blood-brain barrier. Furthermore, they suggest that affinity of a L-alpha-amino acid for the transport system is determined primarily by side-chain hydrophobicity.     

Resolution and Synthesis of Optically Active Alcohols with Immobilized Ovalbumin and Pea Protein as New Bio-catalysts

It was found that ovalbumin stereoselectively oxidized one of the enantiomers of p-substituted racemic alcohols, thereby providing optically active alcohols with high optical purities. It was found out that, when used appropriately in combination with immobilized pea protein, immobilized ovalbumin made it possible to resolve and synthesize racemic 1-(2-naphthyl)ethanol, 1-phenylethanol, and 1-phenyl-1-propanol. Immobilized ovalbumin could be continuously recycled at least three times without lowering the yield and purity of the products. These results suggested that cereals, beans, and ovalbumin might have additional fourth function among conventional foods. Namely, there might contain nutritional, sensory, biologically regulatory and bio-catalytic functions in conventional foods.     

Chemoenzymatic Synthesis of Optically Active Diacylglycerophospholipid Hydroperoxides Derived from Arachidonic Acid

A new derivative of sulfatide, 2-O-α-l-fucopyranosyl sulfatide, was synthesized. The compound inhibited the binding of HL-60 cells, which express sialyl Lewis X, to P- and L-selectin more than the corresponding non fucosylated compound.     

Optically Active Trimethylcyclopropanecarboxylic Acids

Four optically active trimethylcyclopropanecarboxylic acids were prepared from chrysanthemic acids, and their absolute configurations were determined on the basis of chrysanthemic acids whose configuration were already known. Toxicities of several rethronyl esters towards housflies were compared with those of chrysanthemic acids and the cis-acids were proved to be more effective than the trans-acids.     

Reconstitution of Neutral Amino Acid Transport System from Ehrlich Ascites Tumor Cells

Amino acid transport systems for alanine and leucine have been reconstituted into artificial lipid vesicles. Purified plasma membrane vesicles from Ehrlich ascites cells were dissolved in 2% sodium cholate, 1 mM dithiothreitol, 0.5 mM EDTA, a mixture which solubilized approximately 50% of the membrane protein. This solubilized protein fraction was further purified by a combination of ammonium sulfate precipitations, gel filtration, and DEAE-cellulose chromatography. A fraction containing approximately 15 Coomassie blue staining bands on sodium dodecyl sulfate gels was obtained. This material was reconstituted into liposomes, and preliminary results demonstrated transport of alanine and leucine dependent on a sodium gradient. In addition, an electrogenic gradient mediated by valinomycin-induced potassium diffusion seemed to stimulate alanine uptake further.     

Reconstitution of Neutral Amino Acid Transport Systems from Ehrlich Ascites Tumor Cells

Amino acid transport systems for alanine and leucine were reconstituted into artificial lipid vesicles. Purified plasma membrane vesicles from Ehrlich ascites cells were dissolved in 2% sodium cholate, 1mM dithiothreitol, and 0.5 mM EDTA a mixture that solubilized approximately 50% of the membrane protein. This solubilized protein fraction was further purified by a combination of ammonium sulfate precipitations, gel filtration, and DEAE-cellulose chromatography. A fraction containing approximately 15 Coomassie blue-staining bands on sodium dodecyl sulfate gels was obtained. This material was reconstituted into liposomes, and preliminary results demonstrated transport of alanine and leucine dependent on a sodium gradient. In addition, an electrogenic gradient mediated by valino-mycin-induced potassium diffusion seemed to stimulate alanine uptake further.     

Mechanism and Putative Structure of B0-like Neutral Amino Acid Transporters

The Na⁺-dependent transport of neutral amino acids in epithelial cells and neurons is mediated by B⁰-type neutral amino acid transporters. Two B⁰-type amino acid transporters have been identified in the neurotransmitter transporter family SLC6, namely B⁰AT1 (SLC6A19) and B⁰AT2 (SLC6A15). In contrast to other members of this family, B⁰-like transporters are chloride-independent. B⁰AT1 and B⁰AT2 preferentially bind the substrate prior to the Na⁺-ion. The Na⁺-concentration affects the K _m of the substrate and vice versa. A kinetic scheme is proposed that is consistent with the experimental data. An overlapping binding site of substrate and cosubstrate has been demonstrated in the bacterial orthologue LeuT _Aa from Aquifex aeolicus, which elegantly explains the mutual effect of substrate and cosubstrate on each other’s K _m -value. LeuT _Aa is sequence-related to transporters of the SLC6 family, allowing homology modeling of B⁰-like transporters along its structure.     

Mammalian Amino Acid Transport System y+ Revisited: Specificity and Cation Dependence of the Interaction with Neutral Amino Acids

A reevaluation of the specificity of system y⁺, the classical transporter for cationic amino acids is presented. System y⁺ has been defined as a transporter for cationic amino acids that binds neutral amino acids with lower affinity in the presence of Na⁺. The discovery of other transporters for cationic amino has suggested that some properties, originally attributed to system y⁺, may relate to other transport systems. Uncertainty concerns mainly, the affinity for neutral amino acids and the cation dependence of this interaction. Neutral amino acids (13 analogues tested) were found to bind to system y⁺ in human erythrocytes with very low affinity. Inhibition constants (K_iy, mm) ranged between 14.2 mm and >400 mm, and the strength of interaction was similar in the presence of Na⁺, K⁺ or Li⁺ (145 mm). In choline medium, no interaction was detected up to 20 mm of the neutral amino acid. Guanidinium ion (5 mm, osmolarity maintained with choline) potentiated neutral amino acid binding; the effect was most important in the case of l-norvaline which aligned with guanidinium ion is equivalent to arginine. This suggests cooperative interaction at the substrate site. The specificity of system y⁺ was shown to be clearly distinct from that of system y⁺L, a cationic amino acid transporter that accepts neutral amino acids with high affinity in the presence of Na⁺ and which influenced the classical definition of system y⁺. Received: 28 September 1998/Revised: 21 December 1998     

Stereoselective Synthesis of the Optically Active Samin Type of Lignan from L-Glutamic Acid

The optically active samin type of lignan, (1R,2S,5R, 6S)-6-(2-methoxy-4,5-methylenedioxyphenyl)-3,7-dioxabicyclo[3.3.0]octan-2-ol, was stereoselectively synthesized from L-glutamic acid via (2R,3R)-2-[(1S and R)- 1-[(tert-butyldimethylsilyl)oxy]-1-(2-methoxy-4,5-methylenedioxyphenyl)methyl]-3-[(tert-butyldiphenylsilyl)oxy]methyl-1,4-butanediol.     

A Synthesis of Optically Active Key Intermediate for the Synthesis of Optically Active Thromboxanes

An optically active key intermediate, methyl 2, 4-dideoxy-4-C-carboxymethylene-α-d-ribo-hexopyranoside 2′→3 lactone (XII), for the syntheses of optically active Thromboxanes was prepared from d-glucose.     

A Facile Method for Preparation of Polymerizable, Optically Active Ketoprofen Prodrug by Irreversible Lipase-catalysed Resolution

Summary An irreversible resolution of ketoprofen prodrug was developed by lipase-catalysed hydrolysis using corresponding vinyl ester as activated substrate in organic medium. The product obtained, (S)-ketoprofen vinyl ester would be used as a potential prodrug and a significant monomer for polymeric drug. Lipozyme^? immobilized from Mucor miehei showed the highest selectivity and activity after enzyme screening. The effect of solvent, water amount in the reaction medium and reaction temperature on the activity and enantioselectivity of Lipozyme^? was studied. Polymerizable, optically active ketoprofen prodrug could be obtained with excellent enantioselectivity (ee >99%, E ~ 400) in a mixture of dioxane/water (97.5/2.5, v/v) at 25 °C.     

Ontogeny of the Neutral Amino Acid Transporter SNAT1 in the Developing Rat

Summary System A is a highly regulated, Na⁺-dependent transporter that accepts neutral amino acids containing short, polar side chains. System A plays an important role during rat development as decreased pup weights are observed in dams infused during gestation with a non-metabolizable System A substrate. Given the potential importance of SNAT1 during development in the rat brain, we examined whether SNAT1 would be present at an earlier gestation during organogenesis in multiple organs by immunohistochemistry and immunoblotting. SNAT1 protein was observed in the developing lungs, intestines, kidneys, heart, pancreas, and skeletal muscle of rats at prenatal days 14, 17, 19, 21, and postnatal day 2 rats. SNAT1 protein expression decreased in the liver and intestine shortly after birth and as the rat matured. SNAT1 expression was constant throughout development in the lungs and kidney and increased in the heart from prenatal day 19 to postnatal day 2. Highest levels of expression in older animals were seen in organs undergoing rapid cell division.     

Inhibition of Neutral Amino Acid Transport Across the Human Blood-Brain Barrier by Phenylalanine

Abstract: The delivery of large neutral amino acids (LNAAs) to brain across the blood-brain barrier (BBB) is mediated by the L-type neutral amino acid transporter present in the membranes of the brain capillary endothelial cell. In experimental animals, the L-system transporter is saturated under normal conditions, and therefore an elevation in the plasma concentration of one LNAA will reduce brain uptake of others. In this study, we used positron emission tomography (PET) to determine the effect of elevated plasma phenylalanine concentrations on the uptake of an artificial neutral amino acid, [¹¹C]-aminocyclohexanecarboxylate ([¹¹C]ACHC), in human brain. PET scans were performed on six normal male subjects after an overnight fast and again 60 min after oral administration of 100 mg/kg of phenylalanine. The plasma phenylalanine concentration increased by an average of 11-fold between the first and second scans. This increase produced a reduction in [¹¹C]ACHC uptake in all brain regions but not in scalp. The mean ± SD influx rate constant for whole brain decreased after phenylalanine ingestion from 0.036 ± 0.002 to 0.019 ± 0.004 ml/g/min. Kinetic analysis of the effect of plasma phenylalanine concentration on the rate of [¹¹C]ACHC uptake is compatible with a model of competitive inhibition so that large increases in the concentration of one LNAA in plasma will reduce the brain uptake of other LNAAs across the human BBB.     

Complete Amino Acid Sequence of Neutral Protease from Bacillus subtilis var. amylosacchariticus

The neutral protease of Bacillus subtilis var. amylosacchariticus was cleaved chemically or digested with proteolytic enzymes, and the resultant peptides were separated and purified by high performance liquid chromatography. The sequence analyses of these peptides by the manual Edman procedure established the complete amino acid sequence of the enzyme. The neutral protease consisted of 300 amino acid residues with Ala and Leu as its amino- and carboxyl-termini, respectively, and the molecular weight was calculated to be 32,633. The sequence was found to be identical to that of B. subtilis 1A72 neutral protease, which was deduced from nucleotide sequencing. Comparison of the sequence with those of other Bacillus proteases revealed that the putative active site amino acid residues, Zn-binding ligands, and two Ca-binding sites were well conserved among them, as compared with those of thermolysin.     

氨基酸混合液脱色条件的比较选择

以四种粉末状活性炭作为脱色剂,对猪血粉水解液进行脱色比较,结果表明：江西产的４号粉末状活性炭脱色效果最佳。本文还对４号脱色炭的脱色条件进行了摸索研究。     

Novel Synthesis of Optically Active Bishomotyrosine Derivatives Using the Friedel-Crafts Reaction in Triflic Acid

We report here a novel synthesis of optically active bishomotyrosine. The bishomotyrosine skeleton was constructed by using a Friedel-Crafts reaction between phenol and optically active N-Tfa-Glu(Cl)-OMe in triflic acid under the mild condition. Reduction and subsequent deprotection then afforded bishomotyrosine derivatives without any loss of optical purity.