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At least 919 records · Page 51Linked to original sources
PubMed2005

Development of useful reactions based on the novel reactivities of allenic compounds and their application to tandem cyclizations.

This review highlights a recent study on allenic compounds by the author's group. In the first section, the organocopper-mediated ring-opening reaction of ethynylaziridines and palladium-catalyzed reductive synthesis of allenes are described. In the second section, palladium-catalyzed stereoselective cyclization of allenes, including the tandem reaction, leading to aziridines, pyrrolidines, benzoisoindoles, and cyclopropanes is presented. The final section reviews aziridination and medium-ring formation due to the intramolecular reaction of bromoallenes. The latter reaction is based on the author's recent discovery that bromoallenes can act as allylic dication equivalents in the presence of a palladium catalyst and alcohol.

Alkadienes↗
PubMed2006

A novel glucanotransferase from a Bacillus circulans strain that produces a cyclomaltopentaose cyclized by an alpha-1,6-linkage.

A novel glucanotransferase, involved in the synthesis of a cyclomaltopentaose cyclized by an alpha-1,6-linkage [ICG5; cyclo-{-->6)-alpha-D-Glcp-(1-->4)-alpha-D-Glcp-(1-->4)-alpha-D-Glcp-(1-->4)-alpha-D-Glcp-(1-->4)-alpha-D-Glcp-(1-->}], from starch, was purified to homogeneity from the culture supernatant of Bacillus circulans AM7. The pI was estimated to be 7.5. The molecular mass of the enzyme was estimated to be 184 kDa by gel filtration and 106 kDa by SDS-PAGE. These results suggest that the enzyme forms a dimer structure. It was most active at pH 4.5 to 8.0 at 50 degrees C, and stable from pH 4.5 to 9.0 at up to 35 degrees C. The addition of 1 mM Ca(2+) enhanced the thermal stability of the enzyme up to 40 degrees C. It acted on maltooligosaccharides that have degrees of polymerization of 3 or more, amylose, and soluble starch, to produce ICG5 by an intramolecular alpha-1,6-glycosyl transfer reaction. It also catalyzed the transfer of part of a linear oligosaccharide to another oligosaccharide by an intermolecular alpha-1,4-glycosyl transfer reaction. Thus the ICG5-forming enzyme was found to be a novel glucanotransferase. We propose isocyclomaltooligosaccharide glucanotransferase (IGTase) as the trivial name of this enzyme.

Amino Acid Sequence↗
PubMed2002

Design of selectively activated anticancer prodrugs: elimination and cyclization strategies.

Cancer chemotherapy is associated with severe side effects which may be reduced by selective liberation, at the tumour site, of a cytotoxic agent from a non-toxic prodrug. Several strategies are used to achieve the required selective activation: with enzymes which are present in higher concentration in, or close, to the tumour (beta-glucuronidase, plasmin), with enzymes covalently linked to a macromolecular carrier able to recognize antigen positive cancer cells (ADEPT: Antibody Directed Enzyme Prodrug Therapy) or with reductive processes which are favoured in an hypoxic environment. Most of the prodrugs include a linker (or spacer) between the trigger and the drug (or effector). The design of such linkers is crucial in order to achieve a fast drug liberation under physiological conditions. The linker groups may be classified in two categories based on elimination or cyclization processes. The advantages and the limitations of each strategy are discussed.

Animals↗
PubMed1977

The metabolism of a substituted aminoacetamido-benzophenone and cyclization to the corresponding benzodiazepine in the rat in vivo.

1. 2-(5-Cyano-N-methyl-3,5-dimethyl-3-aza-pentanamido)-5-nitrobenzophenone, administered orally to the rat, is well absorbed and extensively metabolized with only minimal quantities of parent compound detected in plasma, bile or urine. 2. Urinary t.l.c. metabolite profiles after oral administration of a substituted aminoacetamidobenzophenone, [14C]C 72 0045, and [14C]nimetazepam were qualitatively similar but differed quantitatively. 3. Analysis by t.l.c. of plasma extracts obtained after oral administration of [14C]C 72 0045 demonstrated that nimetazepam and nitrazepam accounted for 20% of the plasma total radioactivity. Nimetazepam and nitrazepam had a combined concentration up to 22 times greater than the concentration of C 72 0045. 4. The presence of nimetazepam in plasma after oral administration of C 72 0045 was confirmed by mass spectrometry. 5. In the liver, [14C]C 72 0045 was rapidly metabolized to polar metabolites. In the same rats, the major brain metabolites were nimetazepam and nitrazepam. 6. It is concluded that [14C]C 72 0045 undergoes metabolic cyclization in the rat to form nimetazepam, which is further metabolized to form nitrazepam.

Animals↗
PubMed1977

Ring formation in a pentapeptide with alternating L and D residues: an analogy to cyclization in the biosynthesis of peptide antibiotics.

Acetylation of L-isoleucyl-D-alanyl-D-alanyl-L-valyl-D-leucine with acetic anhydride followed by methylation with diazomethane yielded the expected acetylpentapeptide methyl ester with molecular weight 541, but also resulted in the formation of a by-product with molecular weight 555. The incorporation of the mass corresponding to CH2 seems to be due to ring closure--via a mixed anhydride--and methylation of the cyclol derivative thus formed. A preferred, ring-like conformation stabilized by intramolecular hydrogen bonds that in turn are the consequences of the alternation of D- and L- residues in the sequence, is invoked as explanation for the unexpected cyclization. This assumption is supported by the conversion of the pentapeptide methyl ester to desthiomalformain in molten imidazole.

Acetylation↗
PubMed1986

Cyclization of phenylacetyl-L-cysteinyl-D-valine to benzylpenicillin using cell-free extracts of Streptomyces clavuligerus.

Benzylpenicillin, a typical antibiotic produced by some species of fungi, was obtained by direct cyclization of the heteropeptide phenylacetyl-L-cysteinyl-D-valine using cell-free extracts of Streptomyces clavuligerus. This is the first description of evidence of the synthesis of benzylpenicillin from a non natural molecule using a bacterial enzyme.

Cell-Free System↗
PubMed2003

Studies on a second and third ring cyclization in anthracycline biosynthesis.

This paper focuses on study of second and third ring cyclization in anthracycline biosynthesis by a heterologous gene expression. Firstly, anthracycline non-producing Streptomyces peucetius mutant, D2 was heterologously complemented to produce daunomycins with plasmids pSgs44 and pSYE66, which contain putative cyclase genes of S. galilaeus and S. nogalater, respectively. A point mutation in the cyclase gene dpsY of D2 has changed glycine to serine resulting inactivation of the enzyme. Secondly, the putative cyclase gene snoaM from S. nogalater, was expressed in a gene cassette in S. lividans TK24 and S. coelicolor CH999 to study the influence of the cyclase gene on auramycinone production and the impact of endogenous genes on production profiles. The results obtained confirms that a cyclase closing the second and third ring of a polyketide is essential in anthracycline biosynthesis.

Anthracyclines↗
PubMed1987

Potential antitumor agents. II. Lappin intramolecular cyclization of diethyl 3-carbazolylaminomethylenemalonate: a structure assignment.

Diethyl 3-carbazolylaminomethylenemalonate undergoes Lappin cyclization giving 2-carbethoxy-1-oxo-1,4-dihydro-7H-pyrido[2,3-c]carbazole. Formation of an angular pyridocarbazole derivative is consistent with the Markwald rule. The synthesis of 4-ethyl derivatives of the above pyridocarbazole and its 8,9,10,11-tetrahydro derivative is also reported as a goal to potential indoloquinolone antitumoral agents.

Antineoplastic Agents↗
PubMed1986

Kinetics of the intramolecular cyclization of bis(2-chlorethyl)aminoethyl esters of carboxylic acids.

Using a direct protentiometric method the kinetics of the intramolecular cyclization of 12 synthesized bis(2-chlorethyl)-aminoethyl esters of carboxylic acids has been studied. To determine the rate constants of hydrolysis (in 50% water-ethanol medium) the model of successive reactions of first order A----B----C has been used. An attempt has been made to relate the values obtained for the rate constants with the chemical structures of the compounds studied. The kinetic characteristics have been compared to the data of the antileucemic activity of the compounds against tumor models in vivo.

Animals↗
PubMed1996

[Kinetic study of the cyclization of the addition compound of ethyl mercaptoacetate on benzylideneacetophenone].

The study of the kinetic of cyclisation reaction of the additional compound of the mercaptoacetic ethylester on a benzylideneacetophenone was proposed. With the chromatography a retro-Michael reaction was obtained. The H NMR alone permitted to show the order 1 for the kinetic of cyclization and according to the amine used like reaction catalyst, two diastereoisomers could be formed.

Chalcone↗
PubMed1976

[Research on substances with psychotropic activity. IV. Synthesis of 2,3-diphenyl-4-methyl-4H-1,4-benzothiazin-1,1-dioxide by thermal cyclization of N-(2-desylsolfonylphenyl) glycine].

Treatment of the ethyl ester of N-benzoyl-N-(2-benzylsolfonylphenyl)glycine with potassium in benzene gave, by rearrangement, N-(2-desylsolfonylphenyl)glycine, which via thermal intramolecular cyclization and simultaneous decarboxylation gave 2,3-diphenyl-4-methyl-4H-1,4-benzothiazin-1,1-dioxide. The structure of the latter compound was confirmed chemically by oxidising the known 2,3-diphenyl-4-methyl-4H-1,4-benzothiazine with hydrogen peroxide in formic acid and by I;R. and N.M,R; spectral data.

Cyclization↗
PubMed2000

Conformational restriction through C alpha i <--> C alpha i cyclization: Ac12c, the largest cycloaliphatic C alpha,alpha- disubstituted glycine known.

Two complete series of N-protected, monodispersed oligopeptide esters to the pentamer level from 1-aminocyclododecane-1-carboxylic acid (Ac(12)c), an alpha-amino acid conformationally constrained through C(alpha)(i) <--> C(alpha)(i) cyclization, and either L-Ala or Aib residues, along with the N-protected Ac(12)c homopeptide alkylamide series from monomer to trimer, have been synthesized by solution methods and fully characterized. The solution-preferred conformations of these peptides have been assessed by Fourier transform ir absorption and (1)H-nmr techniques. Moreover, the molecular structures of one derivative (Z-Ac(12)c-OH) and three peptides [the tripeptide ester Z-L-Ala-Ac(12)c-L-Ala-OMe, the tripeptide alkylamide Z-(Ac(12)c)(3)-NHiPr, and the tetrapeptide ester Z-(Aib)(2)-Ac(12)c-Aib-OtBu (Aib, alpha-aminoisobutyric acid)] have been determined in the crystal state by x-ray diffraction. The results obtained point to the conclusion that beta-bends and 3(10)-helices are preferentially adopted by peptides based on Ac(12)c, the largest cycloaliphatic C-disubstituted glycine known. A comparison with the structural tendencies extracted from published works on peptides from Aib, the prototype of C-disubstituted glycines, and the other extensively studied members of the class of 1-aminocycloalkane-1-carboxylic acids (Ac(n) c, with n = 3-9), is made and the implications for the use of the Ac(12)c residue in the Ac(n) c scan approach of conformationally restricted analogues of bioactive peptides are briefly discussed.

Alanine↗
PubMed2000

Tautomer-dependent Bergman cyclization of novel uracil-enediyne chimeras

Uracil-enediyne chimeras 4, 7, and 8 were prepared and examined for their propensity to undergo Bergman cyclization. Kinetic experiments showed lactam tautomers 7 and 8 reacted up to 25 times faster than lactim ether 4. Determination of the activation energy for each cycloaromatization reaction, along with radical trapping agent dependent studies, indicate the rate differences result from different ground state energies of the starting enediynes.

Journal Article↗
PubMed2000

All-L-Leu-Pro-Leu-Pro: a challenging cyclization.

In this paper, we report the difficult synthesis of cyclo(Leu-Pro-Leu-Pro). While the cyclization of Leu-Pro-Leu-D-Pro did not cause problems, the all-L-peptide afforded cyclodimer rather than cyclotetrapeptide (cyclomonomer). A first attempt using our reversible backbone substitution methodology failed. However, we were successful in obtaining the desired cyclo(Leu-Pro-Leu-Pro) by decreasing the concentration. The ratio of cyclomonomer to cyclodimer was raised to 1:1.1 using BOP and 1:0.6 using HATU under our high dilution condition. The structures of the cyclopeptides were confidently assigned by electrospray ionization mass spectrometry and NMR.

Cell Division↗