Separation of Fatty Acids as Their p-Bromophenacyl Esters on a C30-Bonded Silica Column by High Performance Liquid Chromatography

Abstract

A new C₃₀-bonded silica column was developed for high performance liquid chromatography. This column was tested for the fractionation of fatty acids as their p-bromophenacyl esters by the reverse-phase mode. Certain pairs of fatty acid esters that are very difficult to separate on a C₁₈-bonded silica column, i. e., arachidonic (C₂₀:4)-palmitoleic (C₁₆:1); elaidic (trans C₁₈:1)-vaccinic (cis C₁₈:1); behenic (C₂₂:0)-nervonic (C₂₄:1); and arachidonic (C₂₀:0)-erucic (C₂₂:1) esters, were completely resolved on the C₃₀-bonded column using solvent gradients of acetonitrile: water and acetonitrile: p-dioxane. A solvent system of methylene chloride: acetonitrile (2:1, v/v) was developed for this column to achieve good separation of a homologous series of extremely nonpolar C₇₆ to C₈₂ α-mycolic acid esters from Mycobacterium tuberculosis H37Ra.     

Azidosphingosine Glycosylation in Glycosphingolipid Synthesis

Abstract

The 3-O-protected azide derivatives of C₁₈-sphingcsine s me 1A-1C reacted with O-acyl protected trichloroacetimidates of D-glucose, D-galactose, and laczose to afford the corresresponding β-glycosides in high yields. Ortho-ester formation in the case of O-acetyl compound could he avoided by increasing the amount of bcrcn trifluoride diethyl ether catalyst. Deprotection. and azido group reduction provided the psychosines of D-gluccse, D-galactose, and lactose (5, 10, and 15), which are versatile intermediates for the attachment of different fatty acii residues. With hexadecanoyl chloride, for instance, the corresponding glycosphingolipids 6, 11, and 16, respectively, were obtained.     

1-Thioglycopyranosyl Esters of N-Acylamino Acids

Abstract

Fully protected 1-thioglycopyranosyl esters of N-acylamino acids (5, 6, and 7) were prepared by condensation of methyl 2, 3, 4-tri-O-acetyl-1-thio-β-d–glucopyranuronate (1), 2, 3, 4-tri-O-acetyl-1-thio-l–arabinopyranose (2), and 2, 3, 4-tri-O-acetyl-1-thio-D-arabinopyranose (3) with pentachlorophenyl esters of N-acylamino acids in the presence of imidazole. The ¹³C NMR chemical shifts of the starting 1-thio sugars and the 1-thiol ester products are reported.     

Synthesis and Reactivity of Benzyl 2-O-Trifluoromethyl-Sulfonyl- and Benzyl 3-O-Trifluoromethylsulfonyl-β-D-Ribofuranoside - The first Evidence of Trifluoromethyl-Sulfonyl (Triflyl) Migration in Carbohydrates

Abstract

Benzyl 2,5-di-O-(tert-bstvldimethvl)silvl-3-O-triflvl-β-D-ribofsranoside (13) underwent triflyl migration upon O-desilylation with triethylammonium hydrogen fluoride in tetrahydrofuran affording benzyl 2-O-triflyl-β-D-ribo-furanoside (7) in ca. 5% yield, together with three other products, benzyl 3-O-triflyl-β-D-ribofuranoside (17), benzyl 2-O-(tert-butyldimethyl)silvl-3-O-triflyl-β-D-ribo-furanoside (18) and benzyl 3-deoxy-β-D-glvceropento-furanos-2-uloside (16). In order to confirm the triflyl migration, a series of reactions were performed.     

Tert-Butyldiphenylsilyl Derivatization for Liquid Chromatography and Mass Spectrometry

Abstract

Tert?butyldiphenylsilyl (TBDPS) derivatization has been investigated for the purposes of improving the HPLC analysis of polar compounds such as fatty acids, cholesterol and bile acids with ultraviolet absorption and/or mass spectral detection. Very mild reaction conditions (room temperature, 30 min) gave quantitative conversion of carboxyls and sterically accessible hydroxyls. The sterically hindered 7α and 12α hydroxyls of bile acids were not silylated to any extent under these conditions. The TBDPS ethers and esters proved stable under HPLC conditions and could be separated on an octylsilyl (RP-8) reverse phase column using acetonitrile as the mobile phase. Detection with an ultraviolet absorption detector at 254 nm was possible but 220 nm provided maximum sensitivity. The derivatives proved to be sufficiently volatile for electron-impact mass spectrometry and the apolar nature of the mobile phase facilitated combined LC/MS with a moving belt interface. The spectra were characterized by abundant ions at [M-57]⁺ due to loss of a tert?butyl radical and m/z 199 due to Ph₂SiOH⁺.     

Synthesis and Reactions of 2,3,4,6-Tetra-O-Acetyl-1-S-(N-Acylaminoacyl)-1-Thio-β-D-Glucopyranoses

Abstract

Fully acetylated 1-thio-β-D-glucopyranosyl esters of N-protected amino acids (4–13) were prepared in high yields by condensation of 2,3,4,6-tetra-O-acetyl-1-thio-β-D-glucopyranose (1) with a pentachlorophenyl esters of N-protected amino acids (2) in the presence of imidazole, or bN-protected amino acids (3) in the presence of DCC + imidazole. High tendency of the S-acyl aglycon group in 4–13 to undergo S → O and S → N migrations was demonstrated in reactions with several alcohols and amines.     

Synthetic Mucin Fragments: Methyl-3-O-(2-Acetamido-2-Deoxy-4-O- and 6-O-β-D-Galactopyranosyl-β-D-Glucopyranosyl)-β-D-Galactopyranoside and Methyl 3-O-(2-Acetamido-2-Deoxy-4-O- and 3-O-Methyl-β-D-Glucopyranosyl-3-D-Galactopyranoside

Abstract

Glycosylation of methyl 3-O-(2-acetamido-3, 6-di-O-benzyl-2-deoxy-β-D-glucopyranosyl)-2,4,6-tri-O-benzyl-β-D-galactopyranoside (2) with 2,3,4,6-tetra-O-acetyl-α-D-galactopyranosyl bromide (1), catalyzed by mercuric cyanide, afforded a trisaccharide derivative, which was not separated, but directly O-deacetylated to give methyl 3-O-(2-acetamido-3,6-di-O-benzyl-2-deoxy-4-O-β-D-galactopyranosyl-β-D-giucopyranosyl)-2,4,6-tri-O-benzyl-β-D-galactopyranoside (8). Hydrogenolysls of the benzyl groups of 8 then furnished the title trisaccharide (9). A similar pflyccsylation of methyl 3-O-(2-acetamido-3-O-acetyl-2-deoxy-β-D-glucopyranosyl)-2,4,6-tri-O-benzyl- β-D-galactopyranoside (obtained by acetylation of 4, followed by hydrolysis of the benzylidene acetal group) with bromide 1 gave a tribenzyl trisaccharide, which, on catalytic hydrogenolysls, furnished the isomeric trisaccharide (12). Methylation of 4 and 2 with methyl iodide-silver oxide in 1:1 dichloro-methane-N, N-dimethylformamide gave the 3-O- and 4-O-monomethyl ethers (13) and (15), respectively. Hydrogenolysis of the benzyl groups of 13 and 15 then provided the title monomethylated disaechartdes (15) and (16), respectively. The structures of trisacchacides 9 and 12, and disaccharides 14 and 16 were all established by ¹³C MMR spectroscopy.     

Derivatives Of α-Cyclodextrin and the Synthesis of 6-O-α-D-Glucopyranosyl-α-Cyclodextrin

Abstract

Regioselective silylation of α-cyclodextrin with tert-butyl-dimethylsilyl chloride in N, N-dimethylformamide in the presence of imidazole gave, in 75% yield, the hexakis(6-O-tert-butyldimethylsilyl) derivative 2, which was transformed into the hexakis(2,3-di-O-methyl, 6-O-methyl, 2,3-di-O-propyl, and 2,3-di-O-acetyl) derivatives. On methanesulfonylation and p-toluenesulfonylation, the hexakis(2,3-di-O-acetyl) derivative 16 afforded the hexakis(2,3-di-O-acetyl-6-O-methylsulfonyl 17 and 2,3-di-O-acetyl-6-O-p -tolylsulfonyl 18) derivatives, respectively. Nucleophilic displacement of 17 and 18 with iodide, bromide, chloride, and azide ions afforded the hexakis(6-deoxy-6-iodo 19, 6-bromo-6-deoxy, 6-chloro-6-deoxy, and 6-azido-6-deoxy) derivatives, respectively, of α-cyclodextrin dodeca-acetate. The hexakis (2, 3-di-O-acetyl-6-deoxy) derivative was prepared from 19. Selective glucosylation of 16 with 2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl bromide under catalysis by halide ion, followed by removal of protecting groups, furnished 6-O-α-D-glucopyranosyl-α-cyclodextrin.     

Separation of Orthophthalaldehyde/Ethanethiol Derivatives of Taurine and Closely Eluting Amino Acids by High Performance Liquid Chromatography

Abstract

In studies of the reverse phase, HPLC analysis of amino acids employing precolumn derivatization with o-phthalaldehyde and ethanethiol, it was shown that α-amino-n-butyric acid, β-amino-isobutyric acid and taurine coeluted in the acetonitrile/aqueous phosphate solvent system. By using a ternary solvent system of acetonitrile/tetrahydrofuran/aqueous phosphate buffer and efficient 5- and 10-μm octadecylsilane packings, the co-elution problem has been resolved. This modified chromatographic system is now being used to quantitatively determine taurine and other closely eluting amino acids in a variety of physiological fluids in order to clarify the role of taurine in human development.     

Spontaneous Aromatization of Diels-Alder Adducts in the Reaction of Alkatrienyl Phosphonates with Alkyl Esters of Acetylencarboxylic Acids

Abstract

The subject of this study was the Diels-Alder reaction involving dialkyl (3-methylpenta-1,2,4-trienyl)phosphonates1a-d, dialkyl(5-methyl-hexa-1,3,4-trienyl)phosphonates 2a-b, and dienophiles (esters of acetylencarboxylic acids) 3a-c, at 65–90°C, in chloroform or with no solvent. The reaction between 1a-d and 3a-b led to the benzyl phosphonates 4a-h, while with 3c it proceeds to a mixture of 5a-d (90%) and 6a-d (10%), which are dialkyl esters of the 3-carboalkoxy(or 2-carboalkoxy)-6-methyl-benzyl phosphonic acid. The intermediate Diels-Alder adducts (A) are not even spectroscopically observable, i.e. in the course of the reaction a 1,5-sigmatropic isomerization occurs, accompanied by aromatization of (A). The isomerization is spontaneous: at ambient temperature 1a-d and 3a-b react slowly and form aromatic compounds:     

Syntheses of α-Amino Phosphinic Acids via Oxo-iminium Salts

Nitrones 2a , 2b obtained from the aldehydes 1a , 1b , are used for the syntheses of the N-ethoxy iminium salts 4a and 4b . In the following procedure 4a and 4b react to several esters of phosphinic acids 6a - 6d .     

Potential Iwternal Standards for the Reversed-Phase High Performance Liquid Chromatography Analysis of Thyroidal Amino Acids

Abstract

Seven analogs of DL-thyroxine (1) were synthesized and evaluated as internal standards for the reversed-phase HPLC analysis of thyroidal amino acids. On the basis of retention time, separation from DL-thyroxine (1), stability, solubility and ease of preparation, 3-[3-(4′-hydroxy-3′,5′-diiodophenoxy)-2,4,6-triiodophenyl)]-DL-alanine (4) appeared to be the best candidate for use as an internal standard.     

Diborane Reduction of O-(Tert-Butyldimethylsilyi.)galactaramides. A Model Study for Aminoalditol Synthesis

Tert-butyldimethylsilylation of dimethyl galactarate (1) with tert-butylchlorodimethylsilane/imidazole/N,N-dimethylformamide at 25 [ddot]C dimethyl 2,5-bis-O-(tert-butyldimethylsilyl)galactarate (2) as the principal product, with methyl 2,3,5-tris-O-(tert-butyldimethylsilyl)-D,L-galactarate-l,4-lactone (3) and methyl 2,3-bis-O-(tert-butyldimethyl)-D,L-galactarate-l,5-lactone (4) as minor products. When the reaction was carried out at 65 [ddot]C, the only product was the 1,4-lactone, 3 Ammonolysis of 2 in methanol gave 2,5-bis-O-(tert-butyldimethyl)-galactaramide (5, 94%), which was conveniently reduced with borane- THF to 1,6-diamino-1,6-dideoxygalactitol, isolated as its dihydrochloride 9. Ammonolysis of 3 in methanol gave a mixture of 5; 2,3,4-tris-O-(tert-butyldimethylsilyl)-D,L-galactaramide (6), 2,3,5-tris-O-(tert-butyldimethylsilyl)-D,L-galactaramide (7), and 2,3,5-tris-Q-(tert-butyldimethylsilyl)-D,L-1,4-lactonogalactaramide (8). Borane-THF reduction of a mixture of 6 and 7 also yielded 9. This study served as a model for the use of O-silylated carbohydrate amides in the preparation of aminodeoxyalditols.     

Darstellung Von β-D-Olivosyl(1→3)-D-olivosiden Aus Mithramycin

Abstract

The benzyl glycoside 4 obtained from 2-bromo-2-deoxy-α-0-quinovosyl bromide 1, readily accessible by the dibromomethyl methyl ether reaction of 2, is deformylated to give the monohydroxy compound 5 which is used in glycosidation reactions. Treatment of 3 with dibromomethyl methyl ether results in the formation of the labile β-furanosyl bromide 7 and the cyrstalline pyranosyl bromide 8 in a ratio of 1:2, both of which are further characterized by their methyl glycosides 10 and 11, respectively. Action of dibromomethyl methyl ether at room temperature on the benzyl ether 6, conventionally prepared from 3, is shown to proceed initially to the glycosyl bromide 9. Compound 9 is cleaved to the 4-formyl-blocked pyranosyl bromide 12, and only after prolonged reaction time gives the pyranosyl halide 8. The glycosidation of the glycosyl bromide 1 with benzyl-4–0-benzyl-α-D-olivoside 13 in the presence of silver carbonate and silicate is a sluggish reaction and gives rather low yields of the β-and the α, l-3-linked disaccharides 15 and 16 in the ratio 3–4:1. With silver triflate the yield is improved to the 61% and the ratio 6:1 in favour of 15.

Further transformations lead to both the syrupy olivosyl olivosides 17. and 18. In a more favourable reaction sequence 1 is condensed with the alcohol component 5 and silver triflate as promoter and yields the crystalline β-(19) and the α, 1→3-linked disaccharides (20) in 92% and a ratio of 6.5: 1. By subsequent transformations the protected title tetradeoxy disaccharide 21 is obtained.     

A Comparison of Fluorescent Pigments From Flavobacterium and Sphingobacterium Species

Abstract

An extraction procedure was developed for the isolation of fluorescent pigments from species of Flavobacterium and Sphingobacterium. This procedure was conducted at room temperature. Thereby the possibility of thermal degradation of the fluorescent pigments present in these organisms was reduced compared to previously reported extraction methods in which pigments were extracted after heating with strong base. Extracts from strains of eight species of these two genera have been evaluated using a video fluorometer (VF). This instrument rapidly provides a two-dimensional fluorescence spectrum of each extract. Data from replicate extracts of the organisms have been compared in order to evaluate the potential for identification of these microorganisms on the basis of their fluorescent pigment content. Similarities between the fluorescence spectra of two of the Flavobacterium species and Sphingobacterium mizutae support earlier studies which have shown that these organisms are related on the basis of their content of menaquinones and cellular fatty acids.     

Efficient purification and complete NMR characterization of galactinol,sucrose, raffinose,and stachyose isolated from Pinus halepensis (Aleppo pine) seeds using acetylation procedure

The use of precipitation followed by acetylation procedures and preparative TLC purification allowed a facile isolation of four carbohydrates from the methanol extract of Pinus halepensis seeds. The isolated oligosaccharides exhibited high degree of purity. They were identified as α-D-galactosyl-(1→1)-myo-inositol nonaacetate (1), α-D-glucosyl-(1→2)-β-D-fructosyl octaacetate (2), α-D-galactosyl-(1→6)-α-D-glucosyl-(1→2)-β-D-frutosyl undecaacetate (3), and α-D-galactosyl-(1→6)-α-D-galactosyl-(1→6)-α-D-glucosyl-(1→2)-β-D-frutosyl tetradecaacetate (4) and were isolated for the first time from this plant. The ¹H and ¹³C NMR assignments for compounds 2, 3, and 4 were detailed herein for the first time.     

SYNTHÉSE DE THIOÉTHERS D'ACIDES PROPYLBORONIQUES S - BENZYLÉS

The protection of the hydroxy group of p-cresol 1 by o-silylation gives derivatives 2 and 3 , the methyl group of which can be brominated by NBS. The phase transfer catalysis applied to 4 and 5 is a good way which permits the mild introduction of the allylthio group ( 6 and 7 ). Hydroboration applied to silylated compounds 8 and 9 , followed by methanolysis and hydrolysis leads to target acids 10 and 11 in a good yield.

La protection du groupement hydroxy du p-crésol 1 par o-silylation donne les dérivés 2 et 3 ce qui permet de bromer le substituant méthyle par le N-bromosuccinimide (NBS). La catalyse par transfert de phase (CTP) appliquée aux produits 4 et 5 est une bonne méthode pour introduire un groupement allylthio (composés 6 , 7 ). L'hydroboration des composés silylés 8 et 9 , suivie d'une méthanolyse et d'une hydrolyse permet d'accéder aux acides cibles 10 et 11 avec de bons rendements.     

NOUVELLE SYNTHÈSE DE [1,2-A]BENZIMIDAZOLO-1,3,5,2-TRIAZAPHOSPHORINES ET DE [1,2-A]BENZIMIDAZOLO-1,3,5,2- TRIAZAPHOSPHORINE-2-THIONES

The condensation of N₁-benzimidazolyl amidines 1 with tris(dimethy- lamino)phosphine leads to the corresponding [1,2a]Benzimidazolo-1,3,5,2-triazaphosphorines 3 . The N₂-phosphoroamidine intermediates 2′ are isolated and yielded the corresponding cyclic compounds 4 upon heating. The oxidation by sulfur of the compounds 3 gives the thiooxide derivatives 4 .

The structure of these compounds is unambiguously confirmed by IR, ¹H, ³¹P, and ¹³C NMR spectroscopy and by MS for some products.     

Oxygenation of Trimethylsilylallenes Readily Obtainable from Organoboranes. Syntheses of 1-Trimethylsilyl-1-alkyn-3-ones and 1-Trimethylsilyl-1-alkyn-3-ols

Abstract

Recently we have reported that the reaction of sodium methoxide with ate-complexes (1) readily prepared from trimethyl-silylpropargyl phenyl ether and organoboranes gives trimethyl-silylallenes (2) selectively (eq. 1).¹ In an attempt to find a new synthetic application of such silylallenes (2), the oxidation of 2 was examined. Although the usual oxidants such as m-chloro-perbenzoic acid were found to be unsuitable for the oxidation of the silylallenes, it was discovered that 2 was autoxidized at room temperature to propargylic hydroperoxide (3) (eq. 2). For example, the acidified starch-iodine test² strongly suggested the presence of the organic hydroperoxide in the reaction mixture obtained from 1,2-heptadienyltrimethylsilane (2, R=Bu) and oxygen. The hydroperoxide (3, R=Bu) was isolated in a 40% yield by distillation, 45–48 [ddot]C/0.1 mmHg. In the infrared spectrum, the OH stretching frequency appears at 3430 cm^?1 and the C°C at 2180 cm,^?1     

Recycling HPLC of p-Bromophenacyl Esters of Saturated C35–56 Fatty Acids from Mycobacterium Tuberculosis H37Ra on a Silica Column

Abstract

The p-bromophenacyl esters of saturated C_35–56 fatty acids from Mycobacterium tuberculosis H37Ra were separated according to structural classes on a silica column by high performance liquid chromatography (HPLC). The sample was cycled five times during HPLC. Highly purified C_35–38 esters were obtained by this method. Further HPLC fractionation on a reverse-phase column (C₁₈-bonded silica) gave complete separation of most of the remaining fractions. By combining mass spectrometry with HPLC separations, many of the fatty acid esters were tentatively identified.