摘要:

The ΔHsandvalues of some one hundred esters belonging to twenty different homologous series are determined experimentally in the polar stationary phase (Carbowax 1540) by gas–liquid chromatography.Correlations between thermodynamic values and the molecular structure of esters are studied. The influence of the number of carbon atoms in the acid and alcohol chains and the position of the carboxylic group and branching chains on the ΔHsandvalues is considered.Faisant appel à la chromatographie en phase gazeuse impliquant du Carbowax 1540 comme phase stationnaire on a déterminé expérimentalement les valeurs de ΔHset ded'une centaine d'esters appartenant à 20 séries homologues différentes.

ISSN:0008-4042    

DOI:10.1139/v81-325

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

2-Methyl-(2-acetamido-3,4,6-tri-O-acetyl-l,2-dideoxy-β-D-mannopyrano)-[2,1-d]-2-oxazoline was efficiently converted into 2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-α-D-mannopyranosyl phosphate, by treatment with dibenzyl phosphate, followed by catalytic hydrogenolysis of the benzyl groups. Similarly, 2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-α-D-glucopyranosyl phosphate and -galactopyranosyl phosphate were synthesized from the respective peracetyl oxazolines. In each case, the procedures for preparing the oxazoline, and conversion into the glycosyl phosphate, were modified to give high yields of pure products. 2-Acetamido-3,4,6-tri-O-acetyl-2-deoxy-α-D-mannopyranosyl phosphate was coupled with 2′,3′-di-O-acetyluridine 5′-monophosphate by a modification of the mixed anhydride procedure, to give 2',3'-di-O-acetyluridine 5′-(2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-α-D-mannopyranosyl diphosphate), which was readily purified by preparative tic andO-deacetylated to give "uridine diphosphateN-acetylmannosamine" in high yield. Similarly, uridine 5′-(2-acetamido-2-deoxy-α-D-glucopyranosyl- and -galactopyranosyl diphosphates) were synthesized by rapid, efficient procedures, not involving ion-exchange chromatography. Uridine 5′-(2-acetamido-2-deoxy-α-D-mannopyranosyl diphosphate) was converted into uridine 5′-(2-acetamido-2-deoxy-α-D-mannopyranosyluronic acid diphosphate), required for biosynthetic studies, without the preparation of a special platinum catalyst. All the synthetic uridine diphosphate sugars were characterized by optical rotation,1H nmr spectrum, and elemental analysis.

ISSN:0008-4042    

DOI:10.1139/v81-326

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Although it is generally accepted that the self-reaction of cumylperoxy radicals is a second-order process, recent reports have cast doubt on the overall validity of this assumption. Therefore we have reinvestigated some aspects of the self-reaction to clarify the kinetic and mechanistic features.Our product studies are entirely consistent with the accepted mechanism for the self-reaction of cumylperoxy radicals and no evidence was obtained for competing reactions. Results obtained with36O2labelled materials confirm the previous conclusion that reversible scission of cumylperoxy radicals to give oxygen and cumyl radicals does not compete significantly with the self-reaction at ambient temperatures. Kinetic studies, under both steady-state and transient conditions, establish clearly that the self-reaction of cumylperoxy radicals is a second order process. A possible explanation is proposed to account for the previous observations which indicated that the self-reaction was a first order process. Further, we show that the changes observed in the esr spectrum of the cumylperoxy radicals, which were attributed to the formation of a complex with cumyl hydroperoxide, are caused by changes in the viscosity of the solution.

ISSN:0008-4042    

DOI:10.1139/v81-327

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

A mixture of at least four glycosides has been isolated from bulbs ofMuscari comosum. Acidic methanolysis of this mixture afforded a crystalline fraction consisting of four diols1adiffering in the configuration at the epimerizable C-20 and/or C-24 centers. Benzoylation of this diol fraction allowed the isolation of one pure dibenzoate, mp 175–176 °C, to which structure1bwas assigned on the basis of chemical and spectral evidence. This allowed the deduction that one of the aglycone moieties was 27-norlanostane triterpene eucosterol4a. This conclusion has been confirmed by identification of4aas the major product of the enzymatic hydrolysis of the glycoside mixture.

ISSN:0008-4042    

DOI:10.1139/v81-328

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

13C Chemical shifts and resolved carbon–proton couplings of 39 deoxybenzoins and 11 acetophenones, most of which have naturally occurring substitution patterns, are assigned. Individual benzene rings turned out to have typical parameters not affected by structural variations in the rest of the molecule. Due to substitutional saturation, however, these benzenoid carbon shifts markedly deviate from increment additivity. A few trends of these deviations are described. Phenolic hydrogens, fixed between hydroxyl and carbonyl oxygen due to internal hydrogen bonding, are shown to give rise to additional carbon-splittings.

ISSN:0008-4042    

DOI:10.1139/v81-329

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

1,3-Dioxacycloheptene and its 2-CH3, 2-OCH3, 2-t-Bu, and 2,2-dimethyl derivatives were studied by1H and13C dnmr methods. Substituent effects and the interpretation of spectral changes in13C nmr at low temperature allow the determination of the most stable conformation of these compounds (TB for1–4band C for5b) and the characterization of the dynamic processes observed for2b,4b, and5b. The differences between the conformational and dynamic properties of the above compounds and their benzo analogs are rationalized in terms of different torsional interactions in the two series.

ISSN:0008-4042    

DOI:10.1139/v81-330

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Two types of solid complexes are isolated by reaction of CH3HgX (X = NO3and ClO4) with 1-methylcytosine (MCy). The CH3Hg+ion is probably bonded to N(3) in the [CH3Hg(MCy)]X compounds. Mercury binding to N(3) and the deprotonated amino group in [(CH3Hg)2(MCy—H)]X is confirmed by X-ray work on the nitrate salt. The crystals are orthorhombic, space groupPbca, witha = 12.014,b = 13.573,c = 16.353 Å, andZ = 8. The structure was refined on 962 independent reflections to anRfactor of 0.038. The CH3Hg+groups are arranged in asynconfiguration and the angles around the mercury-bonded nitrogen atoms are severely distorted to prevent short Hg … Hg contacts. N(3)-coordination in the 1:1 complexes introduces minor changes in the infrared spectra, but the substitution of an amino proton in the 1:2 compounds produces important modifications.1H nmr data in DMSO-d6are reported for both types of compounds. This work emphasizes the important acidity enhancement experienced by the amino protons upon initial coordination to N(3), which facilitates further reaction of CH3Hg+by proton displacement even in acidic media.

ISSN:0008-4042    

DOI:10.1139/v81-331

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Disulfides, sulfenyl chlorides, thiosulfonates, and sulfensuccinimides were evaluated as electrophilic thiating agents for converting the enamine 6-dehydrodeoxynupharidine to α-thiohemiaminal derivatives of the alkaloid deoxynupharidine. Sulfensuccinimides were generally the most useful but other types of agents produced better yields in some individual cases.

ISSN:0008-4042    

DOI:10.1139/v81-332

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Application of the exciton chirality method has confirmed that capsidiol, a unique eremophilane, has the absolute stereochemistry depicted in1. The1H and13Cmr, circular dichroism, and magnetic circular dichroism spectra of capsidiol and 1-epicapsidiol dibenzoates are discussed.

ISSN:0008-4042    

DOI:10.1139/v81-333

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Pyrolysis products from bacterial polyesters, poly-β-hydroxybutyrate (PHB), and from a heteropolyester (β-hydroxyvalerate and β-hydroxybutyrate) were identified. Different physical forms of PHB were studied: PHB purified by dissolution in chloroform, native granules of PHB, and PHB in bacterial cells. The products were characterized by gc, ms, and nmr analysis. The yield of crotonic acid obtained by the pyrolysis of purified PHB was 60 to 65%. Pyrolysis of PHB native granules yielded crotonic acid as well as oligomers of PHB with a terminal crotonate. Upon direct pyrolysis of dry bacterial cells, the yield of crotonic acid was 20 to 25% of the PHB in the cells. From the heteropolymer, 2-pentenoic acid and terminally unsaturated oligomers of polyhydroxyvalerate were obtained. The usefulness of the pyrolysis method for obtaining vinyl compounds from bacterial cultures containing polyalkanoates is discussed.

ISSN:0008-4042    

DOI:10.1139/v81-334

出版商:NRC Research Press    

年代:1981

数据来源: NRC