摘要:

Several procedures for installing a C2 alkoxy group at C2 of a hex-2-enopyranoside have been investigated. The one that is most convenient for large-scale preparation begins with a 2-keto pyranoside, which is converted into the correspondingexomethylene derivative. An SN2′ rearrangement is effected with thionyl chloride, and the resulting primary allylic chloride is displaced with sodium benzylate.

ISSN:0008-4042    

DOI:10.1139/v94-011

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Site-directed mutation was introduced into the gene for the farnesyl diphosphate synthase ofBacillusstearothermophilus. To investigate the significance of the three C-terminal amino acids, where arginine is completely conserved throughout the farnesyl diphosphate synthases of prokaryotes and eukaryotes, three kinds of mutant enzymes, R295V, D296G, and H297L, which have replacements of arginine-295 with valine, aspartate-296 with glycine, and histidine-297 with leucine, respectively, were overproduced and purified to homogeneity. All of the three mutant enzymes showed similar catalytic activities to that of the wild-type enzyme, indicating that the basic amino acids including the conserved arginine in the C-terminal region are not essential for catalytic function. They were also similar to the wild-type enzyme with respect to pH optima, thermostability, reaction product, and kinetic parameters for allylic substrates. However, theirKmvalues for isopentenyl diphosphate are approximately twice that of the wild type.

ISSN:0008-4042    

DOI:10.1139/v94-012

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

sym-Homospermidine, the first pathway-specific intermediate of pyrrolizidine alkaloid (PA) biosynthesis, is formed from two moles of putrescine in an NAD+-dependent reaction catalyzed by homospermidine synthase (HSS). In the overall process catalyzed by HSS, NAD+seems to function as hydride acceptor in the first part of the reaction and subsequently as hydride donor in the second part. This was proved with chirally Cl-deuterated putrescines. Both a bacterial HSS (isolated fromRhodopseudomonasviridis) and the enzyme from PA-producingEupatoriumcannabinumtransformed (R)-[1-2H]putrescine and (S)-[1-2H]-putrescine into homospermidine with a 100% retention of deuterium. Studies with deuterated and14C-labeled substrates revealed that in the presence of putrescine spermidine is a substrate of HSS. The putrescine semialdehyde moiety of spermidine is combined with putrescine and 1,3-diaminopropane is released. Kinetic studies with plant HSS documented that the putrescine semialdehyde moiety of spermidine is incorporated into homospermidine with the same affinity (Km) and activity (Vmax) as putrescine. Plant HSS is highly specific for putrescine and spermidine; spermidine is not a substrate in the absence of putrescine. It is suggested that in the biosynthesis of homospermidine and thus PAs, one of the two C4 units is derived from spermidine and the other one from putrescine. A scheme of the HSS-catalyzed reaction is proposed that fully accounts for the enzymatic data and the results of previous tracer studies. Bacterial HSS is less substrate specific and not as well adapted as plant HSS to accept spermidine as a substrate.

ISSN:0008-4042    

DOI:10.1139/v94-013

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The biosynthesis of the phytotoxin coronatine has been investigated by administration of isotopically labeled precursors toPseudomonassyringaepv.glycinea. The structure of coronatine contains two moieties of distinct biosynthetic origin, a bicyclic, hydrindanone carboxylic acid (coronafacic acid) and a cyclopropyl α-amino acid (coronamic acid). Investigations of coronafacic acid biosynthesis have shown that this compound is a polyketide derived from three acetate units, one butyrate unit, and one pyruvate unit. The two carbonyl oxygen atoms of coronafacic acid were found to be derived from the oxygen atoms of acetate. Additional experiments are described that rule out some possible modes for assembly of the polyketide chain. Coronamic acid is shown to be derived fromL-isoleucine via the intermediacy ofL-alloisoleucine. Examination of the mechanism of the cyclization ofL-alloisoleucine to coronamic acid revealed that the formation of the cyclopropane ring takes place with the removal of only two hydrogen atoms from the amino acid, one at C-2 and the other at C-6. The nitrogen atom at C-2 ofL-alloisoleucine is shown to be retained. On the basis of these observations, a mechanism is postulated for the cyclization reaction that involves the diversion of an enzymatic hydroxylation reaction into an oxidative cyclization. Finally, a precursor incorporation experiment with deuterium-labeled coronamic acid demonstrated that free coronamic acid can be efficiently incorporated into coronatine. This observation indicates that the cyclization ofL-alloisoleucine to coronamic acid can occur before formation of the amide bond between coronafacic acid and coronamic acid.

ISSN:0008-4042    

DOI:10.1139/v94-014

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Septatisine3, an atisane-type diterpenoid alkaloid, was isolated from the roots ofAconitumseptentrionaleKoelle. Its structure was established on the basis of homonuclear1H COSY, LRCOSY, NOESY, DNOE, fixed-evolution HETCOR, and selective INEPT techniques.

ISSN:0008-4042    

DOI:10.1139/v94-015

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The administration of sodium [1-14C] and [2-14C] acetate,L-[U-14C] glutamic acid, &([a-z]+);-amino [U-14C] butyric acid,L-[U-14C] ornithine hydrochloride, and [1,4-14C] putrescine dihydrochloride toTetraponerasp. ants resulted in the formation, for each feeding experiment, of labelled tetraponerine-8 (2). The distribution of radioactivity into2was established by chemical degradation. The results obtained favor the hypothesis that the pyrrolidine ring of tetraponerine-8 is derived fromL-glutamic acid viaL-ornithine and putrescine, while the 12-carbon chain is derived from the combination of six acetate units.

ISSN:0008-4042    

DOI:10.1139/v94-016

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Beginning with (R)-pulegone, a CD3group attached to the stereogenic center containing CH3has been created by conversion to citronellal-1-d, exchange of the acidic hydrogens at C-2 by deuterium, and decarbonylation with Wilkinson's catalyst. Oxidation to isovaleric acid-d3and conversion to leucine by standard procedures gave the (2S,4S) and (2R,4S) diastereomers (10and12) of [5,5,5-2H3]leucine.

ISSN:0008-4042    

DOI:10.1139/v94-017

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

A unique aldolase, which was isolated fromStreptomycesamakusaensis, is used to catalyse a reverse aldol reaction on representative racemic β-hydroxy-α-amino acids (3–6) to give samples of the (2R,3S)-(D-threo)-enantiomers with excellent enantiomeric purity.

ISSN:0008-4042    

DOI:10.1139/v94-018

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Pentalenene synthase catalyzes the cyclization of farnesyl diphosphate (1) to the sesquiterpene hydrocarbon pentalenene (4). Separate incubations of (4S,8S)-[4,8-3H2, 4,8-14C2]farnesyl diphosphate (1a) and (4R,8R)-[4,8-3H2, 4,814C2]farnesyl diphosphate (1b) with pentalenene synthase isolated fromStreptomycesUC5319 and analysis of the derived labeled pentalenenes,4aand4b, respectively, by chemical degradation established that H-8siof FPP was lost upon cyclization to pentalenene. Consideration of the plausible conformations of the enzymatic cyclization intermediates indicates that the electrophilic allylic addition-elimination (SE′) reaction in which the C-4,5 bond of pentalenene is formed involves an orthogonal relationship between the C—C bond being formed and the C—H bond that is ultimately broken.

ISSN:0008-4042    

DOI:10.1139/v94-019

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The structure of macleanine, a unique type of Lycopodium alkaloid, was deduced from its spectroscopic (especially1H and13C nuclear magnetic resonance) properties and from biogenetic considerations. The structure was verified by an X-ray crystallographic study of the hydroperchlorate.

ISSN:0008-4042    

DOI:10.1139/v94-020

出版商:NRC Research Press    

年代:1994

数据来源: NRC