Asymmetric hydrogenation of dehydrodipeptides bearing different protecting groups

Summary.  N-[(Z)-N-Benzoyl- or N-boc-(2-fluorophenyl)dehydroalanyl]-(R)- or (S)-phenyl-alanines 1,2,5 and 6 were hydrogenated in the presence of chiral and achiral rhodium complexes. The optical induction is compared to the results obtained using the corresponding esters as substrates. Received November 11, 2001 Accepted January 15, 2002     

Asymmetric synthesis of 2-arylpiperazines

An asymmetric synthesis of 2-arylpiperazines starting from phenacyl bromides, a variety of which are easily available, has been established. The synthesis features a CBS reduction of phenacyl bromide to provide optically enriched compounds, an S_N2 reaction of 1,2,3-oxathiazolidine 2-oxides with an azide anion with invert of configuration, and construction of the piperazine ring via reduction of piperazine-2,3-diones.     

Solution phase synthesis of the 14-residue peptaibol antibiotic trichovirin I

Summary.  The 14-residue peptaibol antibiotic trichovirin I 4A of the structure Ac-Aib-L-Asn-L-Leu-Aib-L-Pro-L-Ala-L-Val-Aib-L-Pro-Aib-L-Leu-Aib-L-Pro-L-Leuol (Aib = α-aminoisobutyric acid, Leuol = leucinol) was synthesized by stepwise conventional solution phase synthesis using the Z/OtBu(OMe) strategy and HOBt/EDC as coupling reagents. Intermediates were fully characterized and the identity of the synthetic peptide with the component 4A of the natural, microheterogeneous peptide mixture was proven by electrospray mass spectrometry, HPLC, and bioassay. Received March 25, 2002 Accepted June 14, 2002 Published online December 18, 2002 RID="*" ID="*"  Dedicated to Prof. Dr. Günther Jung. Tübingen University, on the occasion of his 65^th anniversary. Authors' address: Prof. Dr. Hans Brückner, Interdisciplinary Research Center, Institute of Nutritional Science, Department of Food Sciences, Justus-Liebig-University of Giessen, Heinrich-Buff-Ring 26, D-35392 Giessen, Germany, Fax: +49-641-99-39149, E-mail: hans.brueckner@ernaehrung.uni-giessen.de Abbreviations: Amino acids are abbreviated according to three-letter-nomenclature; Aib, α-aminoisobutyric acid (2-methylalanine); Iva (isovaline, 2-ethylalanine); Leuol, L-leucinol [(S)-2-amino-4-methyl-1-pentanol]; AAA, amino acid analysis; EI-MS, electron impact mass spectrometry; ESI-MS, electrospray ionization mass spectrometry; HPLC, high performance liquid chromatography; Z, benzyloxycarbonyl; Fmoc, 9-fluorenylmethyoxycarbonyl; OtBu, tertiary butoxy (tert-butylester); OMe, methoxy (methyl ester); OBzl, benzyloxy (benzyl ester); TDM, N,N,N′,N′-tetramethyl-4,4′-diamino-diphenylmethane (Arnold's base); for other abbreviations see Experimental.     

Effect of dietary sulfur amino acids on the taurine content of rat tissues

Summary.  The effect of dietary sulfur amino acids on the taurine content of rat blood and tissues was investigated. Three types of diet were prepared for this study: a low-taurine diet (LTD), normal taurine diet (NTD; LTD + 0.5% Met), and high-taurine diet (HTD; LTD + 0.5% Met + 3% taurine). These diets had no differing effect on the growth of the rats. The concentration of taurine in the blood from the HTD- and NTD-fed rats was respectively 1,200% and 200% more than that from LTD-. In such rat tissues as the liver, the taurine content was significantly affected by dietary sulfur amino acids, resulting in a higher content with HTD and lower content with LTD. However, little or no effect on taurine content was apparent in the heart or eye. The activity for taurine uptake by the small intestine was not affected by dietary sulfur amino acids. The expression level of taurine transporter mRNA was altered only in the kidney under these dietary conditions: a higher expression level with LTD and lower expression level with HTD. Received January 8, 2002 Accepted January 18, 2002 Published online August 20, 2002 Authors' address: Dr. Hideo Satsu, Laboratory of Food Chemistry, Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan, Fax: +81-3-5841-8026 E-mail: asatsu@mail.ecc.u-tokyo.ac.jp Abbreviations: HTD, high-taurine diet; NTD, normal taurine diet; LTD, low-taurine diet; TAUT, taurine transporter; CSA, cysteine sulfinate; CDO, cysteine dioxygenase; CSAD, cysteine sulfinate decarboxylase; PBS, phosphate-buffered saline; DIDS, 4,4′-diisothiocyanostilbene-2′,2′-disulfonic acid     

Inhibition of glutathione synthesis reduces chilling tolerance in maize

 The role of glutathione (GSH) in protecting plants from chilling injury was analyzed in seedlings of a chilling-tolerant maize (Zea mays L.) genotype using buthionine sulfoximine (BSO), a specific inhibitor of γ-glutamylcysteine (γEC) synthetase, the first enzyme of GSH synthesis. At 25 °C, 1 mM BSO significantly increased cysteine and reduced GSH content and GSH reductase (GR: EC 1.6.4.2) activity, but interestingly affected neither fresh weight nor dry weight nor relative injury. Application of BSO up to 1 mM during chilling at 5 °C reduced the fresh and dry weights of shoots and roots and increased relative injury from 10 to almost 40%. Buthionine sulfoximine also induced a decrease in GR activity of 90 and 40% in roots and shoots, respectively. Addition of GSH or γEC together with BSO to the nutrient solution protected the seedlings from the BSO effect by increasing the levels of GSH and GR activity in roots and shoots. During chilling, the level of abscisic acid increased both in controls and BSO-treated seedlings and decreased after chilling in roots and shoots of the controls and in the roots of BSO-treated seedlings, but increased in their shoots. Taken together, our results show that BSO did not reduce chilling tolerance of the maize genotype analyzed by inhibiting abscisic acid accumulation but by establishing a low level of GSH, which also induced a decrease in GR activity. Received: 9 November 1999 / Accepted: 17 February 2000     

Total Synthesis of (+)-(2S,3R)-Piscidic Acid via Catalytic Asymmetric Dihydroxylation of a Trisubstituted Olefin

(+)-(2S,3R)-Piscidic acid was efficiently synthesized with high optical purity (90% e.e.) via Sharpless catalytic asymmetric dihydroxylation of a trisubstituted olefin in only 6 steps from commercially available 4-hydroxyphenylpyruvic acid as the starting material. The reaction proceeded with high optical purity by using the chiral ligands, dihydroquinidine 2,5-diphenyl-4,6-pyrimidinediyl diether or dihydroquinidine 1,4-anthraquinonediyl diether.     

Genetical reachability: When does a sexual population realize all phenotypic states?

 Consider a panmictic, sexual (diploid or polyploid) population where the genotype of an individual is determined by n alleles at a single autosomal locus. Assume that the number of the different phenotypes is also n and that genotype determines phenotype uniquely. It is shown that this population can realize all possible phenotypic states if and only if the hereditary system is either dominant-recessive or maternal or the combination of these. The proof is based on topological degree arguments. Connections to global inverse function techniques are also discussed. Received: 29 July 1997/Revised version: 26 November 1997     

Asymmetric synthesis of N-protected chiral 1-aminoalkylphosphonic acids and synthesis of side chain-functionalized depsiphosphonopeptides.

Optically active 1-aminoalkylphosphonic acid derivatives were synthesized in moderate yields and optical purities via Mannich-type reactions of benzyl carbamate, aldehydes, and optically pure chlorophosphites. Side chain-functionalized depsiphosphonopeptides were also prepared in satisfactory yields directly from one-pot reactions of benzyl carbamate, aldehydes, and diethyl (R,R)-2-chloro-1,3,2-dioxaphospholane-4,5-dicarboxylate.     

Asymmetric synthesis of 2-substituted 4-chromanones using enzyme-catalyzed reactions

2-Substituted 4-chromanones were synthesized in their optically active forms. The chiral intermediates were obtained via lipase-catalyzed enantioselective reactions. Lipase and esterase were also used for the hydrolysis of ester moieties of the precursors of the target compounds under mild conditions.     

The Asymmetric Imino-aldol Approach to the Enantioselective Synthesis of β-amino acids

Two approaches, based on imino-aldol additions, to the asymmetric synthesis of cyclic β-amino acids are reported. In each case a chiral auxiliary was employed attached either to the enolate or to the imine. The relative efficacy of these two synthetic methods is also briefly compared with the former still the preferred route as the latter is currently limited to the preparation of N-sulfonyl β-amino acids.     

Asymmetric protoplast fusions between wild species and breeding lines of potato – effect of recipients and genome stability

 The objective of this study was to investigate if in asymmetric protoplast fusion experiments the ploidy of the recipient line (di-haploid and tetraploid) has an influence on the extent of the asymmetry of the regenerating fusion products. Nineteen different experiments with the wild species Solanum bulbocastanum and Solanum circaeifolium as donors (irradiated with 210 Gy) and different breeding lines (di-haploid and tetraploid) were carried out. The degree of genome elimination was determined by measuring the relative DNA content using flow cytometry. The data showed that the loss of DNA in hybrid plants was significantly higher for 4x, compared to 2x, plants as recipients. In addition, the stability of asymmetry in the fusion products was studied. For this purpose differences in asymmetry in individual shoots originating from the same callus were analysed. A large variation in the DNA content of individual shoots was detected. Of the 4x to 6x shoots 44% had the same DNA content as another shoot originating from the same callus, 19% had a DNA content between 4x and 6x but different from any other analysed shoot originating from the same callus, 2% were chimeras and 35% had a completely different DNA content (eutetraploid, euhexaploid, eupolyploid or asymmetric with a ploidy level above 6x). RFLP-analysis with single-copy probes of 12 regenerates from six calli (two regenerates per callus) confirmed the assumption that the different regenerates of one callus originate from the same single cell. The analysis of selected regenerates cultivated for a period of more than 1 year demonstrated that the genome of asymmetric regenerates might change during cultivation. Received: 30 April 1998 / Accepted: 24 July 1998     

The role of growth hormone and amino acids on brain protein synthesis in aged rats given proteins of different quantity and quality

Summary. The purpose of the present study was to determine whether the regulation of brain protein synthesis was mediated through changes in the plasma concentrations of insulin and growth hormone (GH), and whether the concentrations of amino acids in the brain and plasma regulate the brain protein synthesis when the quantity and quality of dietary protein is manipulated. Two experiments were done on three groups of aged rats given diets containing 20% casein, 5% casein or 0% casein (Experiment 1), and 20% casein, 20% gluten, or 20% gelatin (Experiment 2) for 1 d (only one 5-h period) after all rats were fed the 20% casein diet for 10 d (only 5-h feeding per day). The aggregation of brain ribosomes, the concentration in plasma GH, and the branched chain amino acids in the plasma and cerebral cortex declined with a decrease of quantity and quality of dietary protein. The concentration of plasma insulin did not differ among groups. The results suggest that the ingestion of a higher quantity and quality of dietary protein increases the concentrations of GH and several amino acids in aged rats, and that the concentrations of GH and amino acids are at least partly related to the mechanism by which the dietary protein affects brain protein synthesis in aged rats.     

Asymmetric somatic hybridisation between the annual legumes Medicago truncatula and Medicago scutellata

 Interspecific asymmetric somatic hybrids have been produced between the sexually incompatible annual Medicago species Medicago truncatula and M. scutellata using only one regenerable parent and improved protoplast techniques. Regenerable M. truncatula leaf protoplasts were inactivated by lethal doses of iodoacetamide. Cotyledon protoplasts of non-regenerable M. scutellata were produced from 9 to 13 day old γ-irradiated cotyledons. Polyethylene glycol was used for protoplast fusion, and its successful use depended on a strategy to eliminate toxic effects. More than 50 mature regenerated plants were obtained from the fusion products and amplified fragment length polymorphism and chromosome analysis of a sample of 20 plants allowed the identification of two asymmetric hybrid plants. This technique is suitable for transferring characters from incompatible annual Medicago species to Medicago truncatula. Received: 23 July 1998 / Revision received: 21 December 1998 / Accepted: 15 January 1999     

Phloem transport of amino acids in two Brassica napus L. genotypes and one B. carinata genotype in relation to their seed protein content

 In order to investigate the relationship between the amino acid concentration in the phloem sap of leaves and the protein content in seeds, two Brassica napus genotypes and one B. carinata genotype with low, medium and high seed protein contents were analyzed. Phloem sap was collected from the B. napus winter rapeseed breeding line DSV15 with 19% protein of dry weight in the seeds, the spring cultivar ‘Duplo’ with 25% protein in the seeds and from the B. carinata line BRA1151/90 with 39% protein in the seeds by using the aphid-stylet technique. The total amino acid contents measured in the phloem varied considerably among the three genotypes analysed, and correlated positively with their respective seed protein contents. The total amino acid-to-sucrose ratio was lowest in B. napus line DSV15 which had the lowest seed protein content and highest in the B. carinata line BRA1151/90 which had the highest seed protein content. The amino-N translocation in the phloem during the light period was about 2-fold higher in the B. carinata line BRA1151/90 than in the B. napus lines Dulpo and DSV15. Predominant amino acids in the phloem were glutamine and glutamate, followed by serine, aspartate, and threonine. The amino acid patterns in the leaves resembled those in the phloem, although their absolute concentrations were higher in the phloem than in the cytosol of mesophyll tissue. Furthermore, the concentration gradient of amino acids between the cytosol of mesophyll cells and the phloem was higher in the B. carinata line BRA1151/90 than in the B. napus lines Duplo and DSV15. These results lead to the conclusion that the phloem translocation of amino-N and the phloem loading process of amino acids are decisive factors for the protein content in the seeds of Brassica species. Received: 28 November 1999 / Accepted: 10 April 2000     

Mitochondrial nitric oxide inhibits ATP synthesis. Effect of free calcium in rat heart

Summary.  Nitric oxide is a small potentially toxic molecule and a diatomic free radical. We report the interaction of L-arginine, oxygen and calcium with the synthesis of nitric oxide in heart mitochondria. Nitric oxide synthesis is increased in broken rat heart mitochondria compared with intact and permeabilized mitochondria. Intact mitochondria subjected to hypoxia-reoxygenation conditions accumulated nitric oxide that inhibits oxygen consumption and ATP synthesis. ATPase activity is not affected during this augment of nitric oxide. Physiological free calcium concentrations protected mitochondria from the damage caused by the accumulation of nitric oxide. Higher concentrations of the divalent cation increase the damage exerted by nitric oxide. Received April 15, 2002 Accepted June 17, 2002 Published online November 14, 2002 Acknowledgements This work was supported in part by Mexican Grants from CONACYT (to A.S.M. during its sabbatical) and CIC-UMSNH (2.5). Authors' address: Alfredo Saavedra-Molina, Instituto de Investigaciones Químico-Biológicas, Universidad Michoacana de San Nicolás de Hidalgo, Edificio B-3. C.U., Morelia, Mich. 58030, México, Fax: 52-443-326-5788, E-mail: saavedra@zeus.umich.mx     

Cloning of the polyketide synthase gene atX from Aspergillus terreus and its identification as the 6-Methylsalicylic acid synthase gene by heterologous expression

The geneCAL1 (also known asCDC43) ofSaccharomyces cerevisiae encodes the subunit of geranylgeranyl transferase I (GGTase I), which modifies several small GTPases. Biochemical analyses of the mutant enzymes encoded bycall-1, andcdc43-2 tocdc43-7, expressed in bacteria, have shown that all of the mutant enzymes possess reduced activity, and that none shows temperature-sensitive enzymatic activities. Nonetheless, all of thecall/cdc43 mutants show temperature-sensitive growth phenotypes. Increase in soluble pools of the small GTPases was observed in the yeast mutant cells at the restrictive temperature in vivo, suggesting that the yeast prenylation pathway itself is temperature sensitive. Thecall-1 mutation, located most proximal to the C-terminus of the protein, differs from the othercdc43 mutations in several respects. An increase in soluble Rholp was observed in thecall-1 strain grown at the restrictive temperature. The temperature-sensitive phenotype ofcall-1 is most efficiently suppressed by overproduction of Rholp. Overproduction of the other essential target, Cdc42p, in contrast, is deleterious incall-1 cells, but not in othercdc43 mutants or the wild-type strains. Thecdc43-5 mutant cells accumulate Cdc42p in soluble pools andcdc43-5 is suppressed by overproduction of Cdc42p. Thus, several phenotypic differences are observed among thecall/cdc43 mutations, possibly due to alterations in substrate specificity caused by the mutations.     

Plasma amino acids concentration in amyotrophic lateral sclerosis patients

Summary.  Previous investigations showed an impairment of amino acids (AA) metabolism in amyotrophic lateral sclerosis (ALS). It was hypothesized that excitatory AA may play an important role in the etiopathogenesis of this disease. The aim of the study was to determine plasma AA concentrations in ALS patients, and to examine the relationship between AA and the clinical state of ALS patients, the type of ALS onset and the duration of the disease. The study involved 20 ALS patients and 30 control group people. The AA analysis was performed by ion – exchange chromatography on an automatic AA analyser. The results showed significantly decreased concentrations of valine, isoleucine, leucine, tyrosine and aspartate in the plasma of the whole group of ALS patients compared to the control group, and a significantly decreased concentration of arginine in the patients with a long duration of ALS compared to the patients with a short duration. The clinical state of ALS patients significantly influenced only plasma alanine concentration. Other plasma AA concentrations were not significantly associated with clinical parameters of the disease. Our study confirms that metabolic abnormalities concerning AA exist in ALS patients. However, the normal plasma glutamate concentration observed in this study in the whole group of ALS patients compared to the controls does not exclude that this excitatory AA may play a role in neurodegeneration in ALS. Received June 22, 2002 Accepted October 3, 2002 Published online January 23, 2003 Correspondence: Joanna Iłżecka M.D., Department of Neurology, Medical University, Jaczewskiego 8, 20-954 Lublin, Poland, Fax: +48 81 742 55 34, E-mail: Ilzecka@medscape.com     

Recent advances in asymmetric synthesis of pipecolic acid and derivatives

Summary. This review covers the literature relating to asymmetric syntheses of pipecolic acid derivatives from 1997 to present. This review is organized according to the position and the degree of substitution of the piperidinic cycle. In a first section, syntheses of pipecolic acid itself are described. Then, successively, syntheses of C-3, C-4, C-5, C-6 substituted pipecolic acid derivatives are reported. Finally, syntheses of unsaturated pipecolic acid derivatives are presented before the last part devoted to the polysubstituted pipecolic acid derivatives.     

Asymmetric synthesis of phenanthroindolizidine alkaloids with hydroxyl group at the C14 position and evaluation of their antitumor activities

The asymmetric total synthesis of the strongly cytotoxic phenanthroindolizidine alkaloid 3 was achieved. Using the same route, various derivatives were also synthesized. Cytotoxicity of those synthetic compounds was evaluated and compounds 19, 23, and 27 demonstrated potent cytotoxicities similar to that of 3. The in vivo antitumor efficacy of selected compounds was also evaluated and 23 demonstrated moderate antitumor efficacy.