ISSN:0165-0513    

DOI:10.1002/recl.19941130302

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractThe acid‐catalyzed heterolytic cleavage of the Co‐C bond in coenzyme B12(1) and adocobinamide hydroxide (2) was studied using the excess‐acidity functions ofCoxandYates.The results are compared to the acid‐induced decomposition of methyl(5′‐deoxyribofuranosyl)cobalamin (3) and (2‐ethoxyethyl)cobalamin (4). Evidence is presented to view the bond cleavage in the compounds1, 2and3as anA2mechanism or as anIasubstitution at Co3+, with water as the nucleophile, and in4as anA1mechanism. For1, the temperature dependence (289‐320K) gives ΔS‡ = − 96 J/(K· mol), in agreement with theIa(A2) mechanism. For theA2reactions the volumes of activation [ΔV‡ = −11.4 (1), −8.2 (2) and −11.5 (3) cm3/mol in 2‐4M acid at 298K] are consistent with the proposed mechanism, but ΔV‡ for theA1mechanism of4is exceptionally negative (‐7.2 cm3/mol), probably due to intramolecular coordination in the transition state. A comparison with the much slower acid‐induced decomposition of 5′‐deoxyadenosine brings out the labilization of the furanosyl oxygen bridge by coordination of the 5′‐deoxyadenosyl or 5′‐deoxyribofuranosyl group at the β‐position to cobalt. For 5′‐deoxyadenosine the excess‐acidity treatment and the activation volume

ISSN:0165-0513    

DOI:10.1002/recl.19941130303

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractThe preparation of severala‐fused 3‐pyrazolidinones is described starting from 5,5‐di‐methyl‐3‐pyrazolidinone and using an acid‐induced cyclization of a π‐nucleophile tethered to N‐1 onto a cationic carbon bonded to N‐2 (an exocyclicN‐acylhydrazonium intermediate). The cyclization reactions proceed best with activated π‐nucleophiles such as allyl‐ and propargylsilanes. In the case of an ester substituent at the cationic carbon, structural analogues of antibacterial bicyclic pyrazolidinones are obtained. The stereochemistry of one product is established by X‐ray crystallographic analysis. Two cyclization products showed NMR spectra with very broad signals due to relatively high nitrogen‐inver

ISSN:0165-0513    

DOI:10.1002/recl.19941130304

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

Abstract(1‐13C)‐, (2‐13C)‐, (3‐13C)‐, (3‐13CH3)‐, (4‐13C), and (13CH3O)2‐ ubiquinone‐10 and the corresponding (1‐13C)‐, (6‐13C)‐, (5‐13C)‐, (5‐13CH3)‐, (4‐13C)‐, and (13CH3O)2‐ubiquinone‐0 have been synthesised from simple labelled starting materials via a single reaction scheme. The ubiquinones have been characterised using mass spectrometry,1H NMR and13C NMR. The spectroscopic results indicate that, within experimental error, the syntheses have been accomplished without scrambling or dilution of label. All labelled ubiquino

ISSN:0165-0513    

DOI:10.1002/recl.19941130305

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractThe synthesis, critical micelle concentrations (CMC) and Krafft temperatures (TKrafft) of a series of disodium 2‐(sulfatomethyl)‐1‐alkylsulfates (2a‐d) are presented, with alkyl being n‐tetradecyl (C14), n‐hexadecyl (C16), n‐octadecyl (C18) and n‐eicosyl(C20). The surfactants exhibit a large Ca2+‐tolerance in

ISSN:0165-0513    

DOI:10.1002/recl.19941130306

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractA method for the selective oxidation of the primary hydroxyl functions of polysaccharides is described. The oxidation is mediated by 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO) and hypobromite is used as the regenerating oxidant. At pH 10.5–11 a selectivity of 98% for cold water soluble potato starch and>90% for dahlia inulin wa

ISSN:0165-0513    

DOI:10.1002/recl.19941130307

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19941130301

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY