Determination of D-amino acids labeled with fluorescent chiral reagents, R(-)- and S(+)-4-(3-isothiocyanatopyrrolidin-1-yl)-7-(N, N-dimethylaminosulfonyl)-2,1,3-benzoxadiazoles, in biological and food samples by liquid chromatography

D-Amino acids in food and biological samples labeled with R(-)- and S(+)-4-(3-isothiocyanatopyrrolidin-1-yl)-7-(N, N-dimethylaminosulfonyl)-2,1,3-benzoxadiazoles (DBD-PyNCS) were separated by reversed-phase chromatography and detected fluorometrically at 550 nm (excitation at 460 nm). DL-Amino acids were efficiently labeled at 55 degrees C for 20 min in basic medium. The resulting thiocarbamoyl-amino acids were resolved by an isocratic elution using water:30% methanol in acetonitrile (72:28) containing 0.1% trifluoracetic acid as mobile phase for hydrophilic amino acids and gradient elutions using sodium acetate buffer (pH 5. 2)/acetonitrile as gradient solvent mixture for hydrophobic amino acids, respectively. The detection limits (S/N = 3) of DL-amino acids tested were in the range of 0.16-0.75 pmol. The proposed method was applied to determine the D-amino acid(s) in milk, cream, fermented dairy products (yogurt and yakult), tomato products (juice, puree, and catchup), fermented beverages (beer and red wine), and human urine. The existence of D-amino acid(s) was demonstrated in all the samples tested. Furthermore, the identification of the D-amino acid(s) was performed using both isomers of DBD-PyNCS and by on-line HPLC-electrospray ionization-MS.     

Determination of DL-amino acids, derivatized with R(-)-4-(3-isothiocyanatopyrrolidin-1-yl)-7-(N,N-dimethylaminosulfonyl)-2,1,3-benzoxadiazole, in nail of diabetic patients by UPLC-ESI-TOF-MS

The resolution of free DL-amino acids in human nail was carried out by combination of the R(-)-4-(3-isothiocyanatopyrrolidin-1-yl)-7-(N,N-dimethylaminosulfonyl)-2,1,3-benzoxadiazole [R(-)-DBD-PyNCS] derivatives and UPLC-ESI-TOF-MS. The reaction of the reagent with amino acids effectively proceeds at 55 °C for 20 min in the presence of 1% triethylamine (TEA) to produce the corresponding diastereomers. Each pair of the resulting derivatives was efficiently separated by a gradient program (a mixture of H(2)O and CH(3)CN containing 0.1% formic acid (HCOOH) or 5 mM CH(3)COONH(4) and CH(3)CN) using a reversed-phase ACQUITY UPLC? BEH C(18) (1.7 μm, 100 mm × 2.1 mm i.d.) column and sensitively detected by TOF-MS. The detection limits (S/N=3) of the TOF-MS were 1.0-750 fmol, respectively. A good linearity was achieved from the calibration curves, which was obtained by plotting the peak area ratios of the analytes relative to the internal standard (IS), i.e., 6-aminohexanoic acid, versus the injected amounts of each amino acid (r(2)>0.996), and the intra-day and inter-day assay precisions were less than 8.93%. The derivatives of the free DL-amino acids in human nail were successfully identified by the proposed procedure. As we know, for the first time, these five kinds of D-amino acids, which were D-Ala, D-Val, D-Pro, D-Ile and D-Leu, were found from human nail samples. Fifteen kinds of L-amino acids were also recognized from human nails. Using these methods, the amounts of DL-amino acids in the nails of healthy volunteers and diabetic patients were determined. When comparing the index from diabetic patients to those from healthy volunteers, there is no significant difference in the content of the L-amino acids in the nails. However, a statistically significant (P<0.01) correlation was observed between the D/L-amino acid concentration ratios (Ala, Val, Ile, Leu). Therefore, because the proposed method provides a good mass accuracy and the trace detection of the DL-amino acids in human nails, this analytical technique could be a noninvasive technique to assist in the diagnosis and assessment of disease activity in diabetic patients.     

Cytochrome P-450-dependent oxidation of arachidonic acid to 16-, 17-, and 18-hydroxyeicosatetraenoic acids

Incubation of rat liver microsomal fractions with arachidonic acid in the presence of NADPH results in the formation of three novel monohydroxylated fatty acid metabolites. Utilizing chromatographic and mass spectral techniques, these metabolites have been identified as 16-, 17-, and 18-hydroxyeicosatetraenoic acids. The NADPH-dependent microsomal metabolism of arachidonic acid to 16-, 17-, 18-, and 19-hydroxyeicosatetraenoic acids is induced after animal treatment with beta-naphthoflavone. Reconstitution of the arachidonic acid oxygenase utilizing individual purified cytochrome P-450 enzymes demonstrates regioselectivity, controlled by the protein catalyst, for the hydroxylation of the sp3 carbon atoms adjacent to the methyl end of the fatty acid.     

Conversion of 12-hydroxyoctadecanoic acid to 12,15-, 12,16- and 12,17-dihydroxyoctadecanoic acids with Bacillus sp. U88

Summary A new microbial isolate, Bacillus sp. U88, transformed 12-hydroxyoctadecanoic acid to 12,15-, 12,16- and 12,17-dihydroxyoctadecanoic acids when grown aerobically in 1 % yeast extract medium at 30°C and shaken at 250 rpm for 5 days. These three dihydroxyfatty acids were derivatized with Trimethylsilyl ether and identified by GC-MS analysis. The yield of 12,15-, 12,16- and 12,17-dihydroxyoctadecanoic acids after 5 day incubation were 2.8 %, 7.1 % and 1.1 %, respectively.Names are necessary to report factually on available data; however the USDA neither guarantees nor warrants the standard of the product, and the use of the name by USDA implies no approval of the product to the exclusion of other that may also be suitable.     

Identification of (22R)-3 alpha,7 alpha,12 alpha,22- and (23R)-3 alpha,7 alpha,12 alpha,23-tetrahydroxy-5 beta-cholestanoic acids in urine from a patient with Zellweger's syndrome

The nature of two novel C27 bile acids present as the taurine conjugates in urine from a patient with Zellweger's syndrome was studied. Bile acids conjugated with taurine were isolated from unconjugated and glycine-conjugated bile acids by means of ion-exchange chromatography. After alkaline hydrolysis of the taurine conjugates, the hydrolysate was acidified and extracted with ether; the extract was again subjected to ion-exchange chromatography to separate neutral from acidic compounds. The neutral fraction, which consisted mainly of two steroidal lactones, was treated with lithium aluminum hydride, and the reduction products were identified as (22R)-5 beta-cholestane-3 alpha,7 alpha,12 alpha,22,26-pentol and (23R)-5 beta-cholestane-3 alpha,7 alpha,12 alpha,23,26-pentol by direct comparison of their gas-liquid chromatographic behaviors and mass spectral data with those of chemically synthesized authentic samples. Thus, the chemical structure of two native bile acids present in urine from a patient with Zellweger's syndrome should be formulated as (22R)-3 alpha,7 alpha,12 alpha,22-tetrahydroxy-5 beta-cholestanoic acid and (23R)-3 alpha,7 alpha,12 alpha,12 alpha,23-tetrahydroxy-5 beta-cholestanoic acid, respectively.     

Separation of 17 DL-amino acids and chiral sequential analysis of peptides by reversed-phase liquid chromatography after labeling with R(-)-4- (3-isothiocyanatopyrrolidin-1-yl)-7-(N, N-dimethylaminosulfonyl)-2,1,3-benzoxadiazole

Seventeen DL-amino acids labeled with a fluorescent chiral labeling reagent, R(-)-4-(3-isothiocyanatopyrrolidin-1-yl)-7-(N, N-dimethylaminosulfonyl)-2,1,3-benzoxadiazole (R(-)-DBD-PyNCS), were separated by reversed-phase chromatography and detected fluorometrically at 550 nm (excitation at 460 nm). The reagent reacted with amino functional group in dl-amino acids under basic medium. The thiocarbamoyl derivatives were converted to thiohydantoin via thiazolinone in trifluoroacetic acid (TFA) solution. The epimerization ratios during the reaction of the cyclization were less than 37% in all dl-amino acids tested. The resulting thiohydantoin derivatives of individual dl-amino acids were completely separated with isocratic elutions using acidic mobile phase involving 0.1% TFA. The separations of the thiohydantoins yielded from acidic, basic, neutral, hydroxyl, and aromatic amino acids were good enough for the identification of dl-amino acid. The method using the reagent was adopted to identification of dl-amino acid sequences in eight peptides. The separation and identification of the thiohydantoin derivatives liberated from the peptides labeled were performed by the isocratic elutions. The applicability of the proposed procedure to sequential analysis of peptide was demonstrated with [D-Ala(2)]-leucine enkephalin, [D-Ala(2)]-deltorphin II, d-Phe-Met-Arg-Phe-amide, and Phe-D-Met-Arg-Phe-amide. D-Ala, D-Phe, and D-Met in the peptides were positively identified with the proposed procedures. [L-Ala(2)]-leucine enkephalin, beta-lipotropin, Asp-Ser-Asp-Pro-Arg, and Pro-Asp-Val-Asp-His-Val-Phe-Leu-Arg-Phe-amide were also analyzed as the references without D-amino acid.     

Gestational hyperlipidemia in the rat is characterized by accumulation of n - 6 and n - 3 fatty acids, especially docosahexaenoic acid.

We have evaluated the relative and quantitative changes in long-chain fatty acids in maternal liver, serum, carcass and conceptus (fetuses plus placentae) during pregnancy in the rat, to ascertain whether previous concern over lower proportions of n - 6 and n - 3 fatty acids in maternal serum could be indicative of suboptimal n - 6 or n - 3 fatty acid status. Gestational hyperlipidemia was characterized by proportional decreases in linoleic, stearic and arachidonic acids but increases in palmitic and docosahexaenoic acids. However, the quantitative amount (microgram/ml) of linoleic, arachidonic and docosahexaenoic acids in serum lipids actually increased 2-5-fold from mid-pregnancy to term. Compared to non-pregnant rats, gestational hyperlipidemia was also associated with a lower proportion but similar quantity of linoleic acid in maternal carcass and adipose stores. We conclude that gestational hyperlipidemia in the rat is characterized by a relative but not quantitative decrease in whole-body stores of n - 6 fatty acids and a marked proportional and quantitative increase in docosahexaenoic acid in maternal organs and in the conceptus.     

Stereoisomeric flavour compounds LXVII. 2-, 3-, and 4-Alkyl-branched acids,part 1: General approach to the synthesis of the enantiopure acids

A general approach to the synthesis of 2-, 3-, and 4-alkyl-branched acids of high enantiomeric purity is described. The enantiopure 2-alkyl-branched acids are prepared via liquid chromatographic resolution of diastereomeric phenylglycinol amides and their absolute configuration is deduced from the ¹H-NMR data of the separated diastereomers. Chain elongation methods, by Arndt–Eistert synthesis, via 2-alkylated alkyl carbonitrile or by malonic ester synthesis, are used to prepare 3- and 4-alkyl-branched acids of high configurational purity and known absolute configuration starting from the enantiomeric 2-alkyl-branched acids. © 1994 Wiley-Liss, Inc.     

Steric analysis of 3-, ω4-, ω3- and ω2-hydroxy acids and various alkanols by gas-liquid chromatography

D-Phenylpropionate (PP) derivatives of racemic hydroxy acid methyl esters and alkanols were prepared and the gas-liquid chromatographic separation of diastereoisomers was investigated using QF-1 as stationary phase. Good separations were obtained for the diasteroisomeric PP-derivatives of methyl 3-, 15-, 16-, and 17-hydroxyoctadecanoates. Less separation was observed for methyl 2- and 14-hydroxyoctadecanoates as PP-derivatives and there was no visible separation for PP-derivatives of 4-, 7-, or 13-hydroxyoctadecanoic acid methyl esters. The use of optically active 15-, 16- and 17-hydroxyoctadecanoic acids showed, that in these cases, the diastereoisomers containing L-hydroxy acids had shorter retention times than the ones containing D-hydroxy acids. On the other hand, the D-phenylpropionate derivative of methyl 3D-hydroxydecanoate had shorter retention time than the derivative of its L-enantiomer. PP-derivatives of 3-hexanol, 3-heptanol, 3-octanol, 2-octanol and 2-eicosanol could be resolved by gas-liquid chromatography.     

Distribution of C22-, C24- and C26-α-Unit-Containing Mycolic Acid Homologues in Mycobacteria

There are three mycolic acid homologues with C₂₂-, C₂₄- and C₂₆-α-units in Mycobacterium. In order to reveal the composition and distribution of these homologues in each subclass and molecular species of mycolic acids and to compare them with the composition of constitutive non-polar fatty acids (free and bound forms), we have separated non-polar fatty acids and each subclass of mycolic acids from 21 mycobacterial species by thin-layer chromatography, and analyzed non-polar fatty acid methyl esters by gas chromatography (GC) and the cleavage products of methyl mycolate by pyrolysis GC. We further performed mass chromatographic analysis of trimethylsilyl (TMS) ether derivatives of mycolic acid methyl esters by monitoring [B-29]⁺ ions (loss of CHO from the α-branched-chain structure of mycolic acids) of m/z 426, 454 and 482 which are attributed to C₂₂-, C₂₄- and C₂₆-α-units of TMS ether derivatives of methyl mycolates, respectively, (Kaneda, K. et al, J. Clin. Microbiol. 24: 1060-1070, 1986). By pyrolysis GC, C_22:0, C_24:0 and C_26:0 fatty acid methyl esters generated by the C₂-C₃ cleavage of C₂₂-, C₂₄- and C₂₆-α-unit-containing mycolic acid methyl esters, respectively, were detected. Their proportion was almost the same among subclasses of mycolic acids in every Mycobacterium and also similar to the proportion of constitutive non-polar C_22:0, C_24:0 and C_26:0 fatty acids. By mass chromatography, the composition and distribution of C₂₂- and C₂₄-α-unit-containing homologues were revealed to be similar between α- and α'-mycolic acids in every Mycobacterium. We further analyzed in detail M. vaccae and demonstrated that the mass chromatogram of C₂₂-α-unit-containing homologue was analogous in shape to that of the C₂₄-α-unit-containing one, with the latter mass chromatogram being up-shifted from the former by two carbon numbers, in every subclass of α-, α'-, keto and dicarboxy mycolic acids. The present study suggests that the compositions of three homologues of both mycolic acids and constitutive non-polar fatty acids, which are characteristic to each mycobacterial species, may reflect the proportion of the amount of free C_22:0, C_24:0 and C_26:0 fatty acids synthesized in the cell. It is further demonstrated that intermolecular condensation of two fatty acids which become α- and β-units of mycolic acids will occur independently of the carbon chain length or kinds of polar moieties of fatty acids.     

Synthesis of hydroxy fatty acids from 4, 7, 10, 13, 16, 19-[1-14C] docosahexaenoic acid by human platelets

Human platelets incubated in the presence of 54 microM [1-14C]22:6 produced hydroxydocosahexaenoic acid (HDHE) at about half the rate with which 12-hydroxy-5,8,10,14-eicosatetraenoic acid is produced from [1-14C]arachidonic acid. More than 90% of the radioactivity in HDHE was distributed among two major isomers, 14-HDHE and 11-HDHE. The production of HDHEs was unaffected by indomethacin but completely inhibited by 5,8,11,14-heneicosatetraynoic acid, which suggests that the hydroxy fatty acids are produced by lipoxygenase. The proportions of HDHE isomers varied with the concentration of 22:6. The ratio 14-HDHE/11-HDHE was higher at 6.8 microM 22:6 than when platelets were incubated with 54 microM 22:6. It is suggested that the amounts of these isomers produced will depend both on the availability of 22:6 as well as by competition of this acid with other acids for lipoxygenase.     

Facile syntheses for (5Z,9Z)-5,9-hexadecadienoic acid, (5Z,9Z)-5,9-nonadecadienoic acid, and (5Z,9Z)-5,9-eicosadienoic acid through a common synthetic route

The delta 5,9 fatty acids (5Z,9Z)-5,9-hexadecadienoic acid, (5Z,9Z)-5,9-nonadecadienoic acid, and (5Z,9Z)-5,9-eicosadienoic acid were synthesized for the first time in four steps (9-12% overall yield) starting from commercially available 2-(2-bromoethyl)-1,3-dioxolane. The synthetic approach provided enough material to corroborate the structure and stereochemistry of (5Z,9Z)-5,9-nonadecadienoic acid which was recently identified in the flowers of Malvaviscus arboreus (Malvaceae). The novel phospholipids 1-hexadecanoyl-2-[(5Z,9Z)-5,9-eicosadienoyl]-sn-glycer o-3-phosphocholine and 1-octadecanoyl-2-[(5Z,9Z)-5,9-eicosadienoyl]-sn- glycero-3-phosphocholine were also synthesized from commercially available L-alpha-phosphatidylcholine (egg yolk) and characterized by positive ion electrospray mass spectrometry. These are the first examples of unsymmetrical phospholipids with saturated fatty acids at the sn-1 position and delta 5,9 fatty acids at the sn-2 position.     

ik3-2, a relative to ik3-1/cables, is associated with cdk3, cdk5, and c-abl

A cDNA coding for ik3-2 (designated as ik3-2 from an interactor-2 with cdk3) was cloned by cross-hybridization with ik3-1 and RT-PCR. Analysis of amino acid sequence indicated that ik3-2 has the C-terminal cyclin-box-like region highly homologous to that of ik3-1 (identity in amino acids: 78%). On the other hand, the remainder of ik3-2 gene is not so similar to that of ik3-1. There are several regions other than the C-terminal cyclin-box-like region that are conserved between ik3-1 and ik3-2. In vivo binding assay indicated that like ik3-1, ik3-2 binds to cdk3, cdk5, and c-abl, although ik3-2 binds to cdk3 weakly as compared with ik3-1. The C-terminal cyclin-box-like region of ik3-2 (123 amino acids) is able to be associated with cdk5. Accordingly, ik3-2 is very similar to ik3-1 concerning its molecular interaction with other molecules, suggesting that ik3-2 function in the same biological field as ik3-1. Northern blot analysis indicated that ik3-2 is expressed ubiquitously all over tissues.     

The amino acid requirements of rabbit fibroblasts,strain RM3-56

Strain RM3-56 of rabbit fibroblasts was found to require arginine, cystine, glutamine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, serine, threonine, tryptophan, tyrosine, and valine for growth in a medium containing 2 per cent dialyzed serum as the only undefined component. The requirement for serine is less specific than that of the other 13 amino acids and it is partially replaced by glycine, or alanine, or by several combinations of so called accessory amino acids. The concentrations of essential amino acids which permit maximal proliferation range from 0.005 to 0.3 mM. Cystine, glutamine, lysine, tryptophan, tyrosine, valine are toxic at concentrations of 5 mM. The rate of proliferation of RM3-56 in a medium containing all 14 essential amino acids is increased significantly by the addition of alanine and to a lesser extent by the addition of aspartic and glutamic acids and glycine. A deficiency of cystine or glutamine results in cellular degeneration within 3 to 5 days, whereas the cells remain in good condition for 2 to 3 weeks in the absence of each of the remaining 12 essential amino acids. The results obtained with RM3-56 are compared with strains HeLa, L, and U12, whose amino acid requirements have been investigated under similar conditions.     

De novo synthesis of (Z)- and (E)-7-hexadecenylitaconic acids by a selective lignin-degrading fungus, Ceriporiopsis subvermispora

Ceriporic acids are a class of alk(en)ylitaconic acids produced by a selective lignin-degrading fungus, Ceriporiopsis subvermispora. Their structural units have similarity with biologically important lichen acids, such as chaetomellic and protolichesterinic acids. The unique function of alkylitaconic acid is the redox silencing of the Fenton reaction system by inhibiting reduction of Fe(3+). As estimated by the catalytic function of Delta9-desaturases, 7-hexadecenyl derivatives bearing a trans configuration have not been reported in the family of alk(en)ylitaconic acids, i.e. the structurally similar lichen acids-alk(en)ylcitraconic and paraconic acids. In this paper, we discuss the isolation of an itaconic acid derivative with an (E)-7-hexadecenyl chain from cultures of C. subvermispora. To identify the natural metabolite, (E)- and (Z)-7-hexadecenylitaconic acids were chemically synthesised. The isolated metabolite was identical to the synthetic (E)-hexadecenylitaconic acid and was designated as ceriporic acid D. Administration of (13)C-[U]-glucose demonstrated that ceriporic acid C and trans-7-hexadecenylitaconic acid (ceriporic acid D) were biosynthesised de novo by C. subvermispora.     

2-(N-Fmoc)-3-(N-Boc-N-methoxy)-diaminopropanoic acid, an amino acid for the synthesis of mimics of O-linked glycopeptides

Amino acids with N-alkylaminooxy side chains have proven effective for the rapid synthesis of neoglycopeptides. Chemoselective reaction of reducing sugars with peptides containing these amino acids provides glycoconjugates that are structurally similar to their natural counterparts. 2-(N-Fmoc)-3-(N-Boc-N-methoxy)-diaminopropanoic acid (Fmoc: 9-fluorenylmethoxycarbonyl; Boc: t-butyloxycarbonyl) was synthesized from Boc-Ser-OH in >40% overall yield and incorporated into peptides by standard Fmoc chemistry based solid phase peptide synthesis. The resulting peptides are efficiently glycosylated and serve as mimics of O-linked glycopeptides. The synthesis of this derivative greatly expands the availability of the N-alkylaminooxy strategy for neoglycopeptides.     

Sequence analysis of the murine Hox-2.2, -2.3, and -2.4 homeo boxes: evolutionary and structural comparisons

We have determined the nucleotide sequences and deduced the amino acid sequences of three tandemly arranged murine boxes of the Hox-2 homeo box gene complex on mouse chromosome 11 (Hox-2.2, -2.3, and -2.4). The type and position of differences with other sequenced homeo boxes were analyzed. Hox-2.2 is nearly identical with its cognate human homeo box Hu-2. Hox-2.3 shares 59 of 61 amino acids with the Antennapedia homeo domain of Drosophila and the MM-3 homeo domain of Xenopus and shows 60 of 61 amino acid identity with human HuC1. Hox-2.3, MM-3, and HuC1 also share a stretch of six glutamic acid residues followed by a stop codon 15-20 amino acids 3' of the homeo domain. Hox-2.4 is relatively divergent from most of the other homeo boxes sequenced to date; however, it matches the Hox-3.1 murine homeo domain at 60 of 61 positions. Sequence comparisons with other murine homeo domains, together with previous studies of their genomic organization and chromosomal location, provide support for the hypothesis of a large-scale duplication resulting in the two major murine homeo box gene complexes Hox-1 and Hox-2.     

Metabolism of n -9, n -6 and n -3 fatty acids in hepatoma Morris 7777 cells. Preferential accumulation of linoleic acid in cardiolipin

The objective of this study was to investigate, using a pulse-chase technique, the different incorporation of (1-(14)C) n -9, n -6 and n 3 fatty acids into hepatoma lipids and their secretion to the culture medium. Docosahexaenoic acid (DHA) accumulated preferentially into the triacylglycerol while arachidonic acid (AA) did into the phospholipid fraction. DHA was poorly secreted to the culture medium whereas AA was secreted to a large extent. The fatty acids were initially esterified mainly into phosphatidylcholine and phosphatidylethanolamine. During the 24 h chase, a general shift from phosphatidylcholine to phosphatidylethanolamine was observed. Linoleic acid was esterified in cardiolipin to a much greater extent than any other fatty acid and it was not converted to more polyunsaturated fatty acids.The supplementation of the culture medium with polyunsaturated fatty acids had no inhibitory effect on the growth of the hepatoma cells, in marked contrast to observations made in other tumoral cells. The reasons for the resistance of the hepatoma cells to polyunsaturated fatty acid toxicity, including the possible antioxidant effect of linoleic acid accumulation in cardiolipin, are also discussed.     

Human placental delta5-3beta hydroxysteroid dehydrogenase activity (delta5-3beta HSDH): intracellular distribution, kinetic properties, retroinhibition and influence of membrane delipidation.

Delta5-3beta HSDH activity has been assayed either by spectrophotometric method or by use of radioactive substrates. The enzymatic activity is equally distributed between mitochondrial and microsomal fractions verified by electronic microscopy. The specific activity is comparable in both fractions, as well as the optimal pH and the Km for NAD and for the substrates. The delta5-3beta Hut optimal pH, specific activity and sensitivity to the inhibitory action of various steroids are different when C19 and C21 steroids are used as substrates. Estrogens and cyclic AMP have also an inhibitory action on the oxidation of C21 steroids. Treatment of microsomal or mitochondrial membranes with phospholipase A releases fatty acids (mainly arachidonic) and decreases the enzymatic activity. "Adsorbtion" of the fatty acids on bovine serum albumin partially reactivates the delta5-3beta HSDH.     

Synthesis of the protected 6-16 segment of zervamicin 11-2, an application of the azirine/oxazolone method.

The protected 11 amino acid segment (6-16) of the peptaibol zervamicin II-2 was synthesized by using the 'azirine/oxazolone method' for the introduction of all Aib residues. Whereas a 2,2-dimethyl-2H-azirin-3-amine was used as the building block for Aib(7), methyl 2,2-dimethyl-2H-azirine-3-prolinate and -3-(3-hydroxyprolinate) proved to be ideally suited as dipeptide synthons for the introduction of Aib-Pro and Aib-Hyp, respectively. The coupling of Z-protected amino acids or peptide acids with the 2H-azirin-3-amines were performed in 75% to quantitative yield.