Synthesis of a series of fully methylated aldobiouronic acids,and β-elimination reactions of their synthetic precursors

Treatment of methyl 2,3,4-tri-O-acetyl-l-bromo-l-deoxy-α-d-glucopyranuronate severally with 2,4,6-, 2,3,6-, and 2,3,4-tri-O-methyl derivatives of methyl α-d-glucopyranoside and with methyl 4,6-O-benzylidene-3-O-methyl-α-d-glucopyranoside, in the presence of silver carbonate, afforded crystalline aldobiouronic acid derivatives in high yield. Deacetylation followed by methylation gave a series of fully methylated derivatives of laminaribiouronic, cellobiouronic, and gentiobiouronic acids, and the (1 → 2)-linked analogue. Methylation with methyl iodide and silver oxide in N,N-dimethylformamide was invariably accompanied by a small amount ofβ-elimination, with the formation of olefinic disaccharides which were also obtained by β-elimination reactions of the precursor acetates followed by methylation. Methyl 4,5-unsaturated 4-deoxyhexopyranosyluronate derivatives were the main products of the reaction, but these underwent further degradation with cleavage of the interglycosidic linkage and formation of 6-methoxycarbonyl-4-pyrone.     

Raman spectra of imino acids and poly-L-hydroxyproline

The Raman spectra of poly-L -hydroxyproline in the solid state and aqueous solution have been obtained. From the spectra, the conformations of the polypeptide in the solid and aqueous solution are found to be the same. Major differences in the spectra between the solid and solution are traced to environmental influences of the pyrrolidine group as indicated by studies of the monomers. The Raman spectra of the imino acids, proline and hydroxyproline, as the dipolar ions, the hydrochlorides, and the sodium salts are also reported.     

Mass spectrometry of uronic acid derivatives. XI--Structure elucidation by mass spectrometry of aldobiouronic and pseudoaldobiouronic acids and their beta-elimination products as per-o-methyl derivatives

Electron impact mass spectra of a series of aldobiouronic and pseudoaldobiouronic acid per-O-methyl derivatives and of the corresponding 4,5-unsaturated analogues, found normally among the products of methylation of uronic acid containing disaccharides as a result of methylation accompanying beta-elimination, have been studied. Using labelling experiments, metastable transition measurements and high resolution mass spectrometry, the fragmentation mechanisms of substances of this class have been deduced. Application of the information to the structure elucidation of this type of compound is discussed. It is concluded that from the mass spectra alone it is possible to determine the molecular weight, the cycle masses as well as the mode of linkage between the monomeric units. The appearance potentials of ions formed by cleavage of the glycosidic linkages have also been determined and the energetic differences encountered in the fission of the glycosidic linkages of various types of uronic acid containing oligosaccharides are discussed.     

Biosynthesis of tunicamycin and metabolic origin of the 11-carbon dialdose sugar,tunicamine

Tunicamycin is a reversible inhibitor of polyprenol-phosphate: N-acetylhexosamine-1-phosphate translocases and is produced by several Streptomyces species. We have examined tunicamycin biosynthesis, an important but poorly characterized biosynthetic pathway. Biosynthetic precursors have been identified by incorporating radioactive and stable isotopes, and by determining the labeling pattern using electrospray ionization-collision induced dissociation-mass spectrometry (ESI-CID-MS), and proton, deuterium, and C-13 nuclear magnetic resonance (NMR) spectroscopy. Preparation and analysis of [uracil-5-(2)H]-labeled tunicamycin established the complete ESI-CID-MS fragmentation pathway for the major components of the tunicamycin complex. Competitive metabolic experiments indicate that 7 deuteriums incorporate into tunicamycin from [6,6'-(2)H,(2)H]-labeled D-glucose, 6 of which arise from D-GlcNAc and 1 from uridine and/or D-ribose. Inverse correlation NMR experiments (heteronuclear single-quantum coherence (HSQC)) of (13)C-labeled tunicamycin enriched from D-[1-(13)C]glucose suggest that the unique tunicamine 11-carbon dialdose sugar backbone arises from a 5-carbon furanose precursor derived from uridine and a 6-carbon N-acetylamino-pyranose precursor derived from UDP-D-N-acetylglucosamine. The equivalent incorporation of (13)C into both the alpha-1" and beta-11' anomeric carbons of tunicamycin supports a direct biosynthesis via 6-carbon metabolism. It also indicates that the tunicamine motif and the alpha-1"-linked GlcNAc residue are both derived from the same metabolic pool of UDP-GlcNAc, without significant differential metabolic processing. A biosynthetic pathway is therefore proposed for tunicamycin for the first time: an initial formation of the 11-carbon tunicamine sugar motif from uridine and UDP-GlcNAc via uridine-5'-aldehyde and UDP-4-keto-6-ene-N-acetylhexosamine, respectively, and subsequent formation of the anomeric-to-anomeric alpha, beta-1",11'-glycosidic bond.     

Mass spectra of acetylated derivatives of sialic acids

The fragmentation pattern in electron-impact mass spectrometry has been established for the peracetylated methyl ester methyl glycoside derivative of N-acetylneuraminic acid. The resulting, data allow the interpretation of the mass spectrum of the corresponding derivative of a new sialic acid isolated from the starfish Distolasterias nipon which is shown to be 8-O-methyl-N-acetylneuraminic acid.     

Absorption and fluorescence spectra of ring-substituted indole-3-acetic acids

The absorption and fluorescence spectra of indole-3-acetic acid (1), a plant growth regulator (auxin) and experimental cancer therapeutic, 29 ring-substituted derivatives and the 7-aza analogue (1H-pyrrolo[2,3b]pyridine-3-acetic acid) are compared. Two to four absorbance maxima in the 260-310-nm range are interpreted as overlapping vibronic lines of the 1La<--1A and 1Lb<--1A transitions. Two further maxima in the 200-230-nm region are assigned to the 1Ba<--1A and 1Bb<--1A transitions. 4- and 7-Fluoroindole-3-acetic acid exhibit blue shifts with respect to 1, most other derivatives show red shifts. All indole-3-acetic acids studied, with the exception of chloro-, bromo- and 4- or 7-fluoro-derivatives, fluoresce at 345-370 nm when excited at 275-280 nm. 7-Azaindole-3-acetic acid emits at 411 nm. The fluorescence quantum yield of 6-fluoroindole-3-acetic acid significantly exceeds that of 1 (0.3); the other derivatives have lower quantum yields. The plant-growth promoting activity of the ring-substituted indole-3-acetic acids studied correlates with the position of the 1Bb<--1A transition band.     

Synthesis and mass spectra of esters of branched chain fatty acids

The Wittig reaction between alkylidene triphenylphosphoranes [R — CH = P(C₆H₅)₃, where R varied from H to n — C₁₇H₃₅] and methyl 12-oxooctadecanoate or methyl 10-oxohexadecanoate in dimethylformamide (DMF) has been employed in the synthesis of a partial homologous series of esters of branched chain fatty acids in high yields. The effect of various ratios of reactants in both DMF and dimethylsulfoxide (DMSO) was investigated. Purification from triphenylphosphine oxide was readily accomplished by chromatography on a column of silicic acid-Celite impregnated with silver nitrate.     

Far-infrared spectra of copoly(- -amino acids)

Far-infrared spectra in the region from 700 to 200 cm^?1 were measured for the copolymers of L -alanine and glycine, those of L -alanine and L -valine, those of L -alanine and L -leucine, and those of L -alanine and L -phenylalanine. The observed spectra were interpreted on the basis of the analysis of the far-infrared spectra of the corresponding homopolymers, and the correlation between the conformations of the copolymers and the kinds of the component amino acids was discussed.     

Chemical etiology of nucleic acids: aminopropyl nucleic acids (APNAs)

Aminopropyl nucleic acids (APNAs) are constitutionally simple nucleic acid alternatives with one stereogenic center per nucleotide, and with the potential to hybridize with RNA and to exert catalytic functions. We have developed a protecting group strategy to synthesize APNAs, although in a not very efficient way. Isolation and purification of APNAs proved to be difficult. Their structures might be more suited to function as potential catalytic polymers than as information systems that may evolve into RNA.     

Matrix-method calculation of linear and circular dichroism spectra of nucleic acids and polynucleotides

Calculations of the optical properties (absorption, linear dichroism, circular dichroism, and anisotropic components of the CD) are presented for polynucleotides of random or regular sequence within the formalism of the matrix method using a set of parameters that includes only the ππ* transitions of the aromatic bases. Experimental solution spectra agree favorably with calculated CD spectra for A-RNA, A-DNA, and B-DNA, when coordinates derived from x-ray studies on fibers are used. Excessive hypochromicity is predicted when parameters intended to reproduce the vacuum-uv absorption of the chromophores are included in the calculations, but total elimination of these parameters leads to an insufficient hypochromicity for the long-wavelength absorption band. Using alternative conformations for DNA in low-salt aqueous solution did not improve the agreement between experimental and calculated spectra, but some features of the optical properties predicted for these variant structures suggest that the tilt of the bases with respect to the helical axis may be larger than that of the fiber B-form. In the case of polynucleotides with regular structure, which have been traditionally less easy to understand in terms of the standard nucleic acid conformations, a series of alternative structures has been examined. Unexpectedly, the calculated spectrum for the Z-DNA structure compares almost quantitatively with the experimental spectrum of poly(dGC·dGC) in low salt. This result, which confirms a recent report [Vasmel, H. & Greve, J. (1981) Biopolymers 20 , 1329–1332], is in contrast with the current identification of Z-DNA with the high-salt form of poly(dGC·dGC). Finally, the optical properties of single-stranded polyribonucleotides appear to be better explained when alternative structures [9₁-helix for poly(rA) and 6₁-helix for poly(rC)] are introduced instead of the A-RNA form.