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PubMed1998

Kinetic studies of the branched chain amino acid preferring peptidase activity of the 20S proteasome: development of a continuous assay and inhibition by tripeptide aldehydes and clasto-lactacystin beta-lactone.

We have developed an assay to continuously monitor the branched amino acid preferring peptidase (BrAAP) activity of the proteasome. This assay is based on the hydrolysis of the fluorogenic peptide, Abz-Gly-Pro-Ala-Leu-Ala-Nba (Abz is 2-aminobenzoyl and Nba is 4-nitrobenzylamide) which is cleaved exclusively at the Leu-Ala bond by the 20S proteasome with a kc/Km value of 13 000 M-1 s-1. Hydrolysis of this peptide is accompanied by an increase in fluorescence intensity (lambda ex = 340 nm, lambda em = 415 nm) due to release of the internally quenched 2-aminobenzoyl fluorescence that accompanies diffusion apart of the hydrolysis products, Abz-Gly-Pro-Ala-Leu and Ala-Nba. Using this assay, we examined inhibition of the BrAAP activity of the proteasome by a series of tripeptide aldehydes, Z-Leu-Leu-Xaa-H. When Xaa = Phe, (p-Cl)Phe, and Trp we observe biphasic or partial inhibition of the BrAAP activity. In contrast, when Xaa = Nva and Leu, simple inhibition kinetics are observed and allow us to calculate Ki values of 120 nM and 12 nM, respectively. The inhibitors that exhibit simple inhibition kinetics for BrAAP activity are also approximately equipotent for inhibition of the chymotrypsin-like (ChT-L) and peptidyl-glutamyl peptide hydrolyzing (PGPH) activities, dissociation constants varying by less than 25-fold, whereas the inhibitors that exhibit biphasic inhibition kinetics for BrAAP activity are >300-fold more potent for inhibiting ChT-L activity than for PGPH activity. Inactivation of the BrAAP activity of the proteasome by clasto-lactacystin beta-lactone is also biphasic. beta-Lactone inactivates approximately 60% of the BrAAP activity rapidly, with kinetics indistinguishable from its inactivation of the chymotrypsin-like activity. The remaining 40% of the BrAAP activity is inactivated by beta-lactone at a 50-fold slower rate, with kinetics indistinguishable from its inactivation of the PGPH activity. These results suggest a mechanism in which hydrolysis of Abz-Gly-Pro-Ala-Leu-Ala-Nba (i.e., BrAAP activity) occurs at two different active sites in the 20S proteasome, and that these two active sites are the same ones that catalyze the previously described ChT-L and PGPH activities.

Aldehydes↗
PubMed2002

Synthesis of seven-membered lactones via nickel- and zinc-catalyzed highly regio- and stereoselective cyclization of 2-iodobenzyl alcohols with propiolates.

A new class of substituted seven-membered lactones 3 were conveniently synthesized via cyclization of o-iodobenzyl alcohol 1 (o-IC(6)H(4)CH(2)OH) with various propiolates 2 (RC triple bond CCOOMe) in the presence of Ni(dppe)Br(2) and Zn powder in acetonitrile at 80 degrees C. The catalytic reaction is highly regio- and stereoselective affording seven-membered lactones in moderate to good yields. This methodology can be successfully extended to various substituted o-iodobenzyl alcohols. An intermediate 7 was obtained from the reaction of 1a with methyl 2-octynoate (2a) in the presence of Ni(dppe)Br(2) and Zn at room temperature. A mechanism involving an unusual E/Z isomerization of the carbon-carbon double bond of 7 prior to lactone formation is proposed to account for the catalytic reaction.

Alkynes↗
PubMed2006

Mechanism of wine lactone formation: demonstration of stereoselective cyclization and 1,3-hydride shift.

The cyclization mechanism of (E)-2,6-dimethyl-6-hydroxyocta-2,7-dienoic acid to wine lactone under acidic aqueous conditions was investigated using the two stereoselectively deuterium-labeled precursors (2E,6R,7Z)-[8-2H]-2,6-dimethyl-6-hydroxyocta-2,7-dienoic acid and (2E,7E)-(+/-)-[8-2H]-2,6-dimethyl-6-hydroxyocta-2,7-dienoic acid. A detailed analysis of the generated wine lactone isomers by enantioselective multidimensional gas chromatography (MDGC)/ion trap tandem mass spectrometry demonstrates that the formation of wine lactone proceeds via a nonenzymatic stereoselective cationic cyclization cascade that includes a 1,3-hydride shift. Usually, such mechanisms are features of cyclization reactions that are catalyzed by terpene cyclases. This nonenzymatic conversion of an acyclic precursor to a bicyclic monoterpene under relevant cationic cyclization conditions has rarely been observed and confirms recent suggestions that the precursor itself can provide the chemical functionality required for specific steps in the cyclization cascade.

Cyclization↗
PubMed1992

Electrophilic opioid ligands. Oxygen tethered alpha-methylene-gamma-lactone, acrylate, isothiocyanate, and epoxide derivatives of 6 beta-naltrexol.

O6-Ether derivatives of 6 beta-naltrexol in which the ether substituent includes various electrophilic groups have been synthesized in an effort to examine structure-activity requirements at the 6 beta-substituent for receptor affinity and irreversibility of binding in opioid receptor preparations. A series of tethered 6 beta-ethers having terminal epoxides, alpha-methylene-gamma-lactones, and an isothiocyanate group were prepared. The stereochemistry of the alpha-methylene-gamma-lactones was established by convergent synthesis of their reduction products from epoxides of known absolute stereochemistry. In general, the tested compounds showed comparable affinity and selectivity for the receptor subtypes. All were found with high affinity for mu-sites. The terminal epoxide ether diastereomers 8 and 9 were not bound irreversibly in the assay for total opioid receptors. The alpha-methylene-gamma-lactone diastereomers 10 and 11, and their O14-acetyl precursors 20 and 21, respectively, varied in their irreversible effects, but where noted these effects were mu-site selective. Methacrylate ether 7 and isothiocyanate ether 12 were bound irreversibly at both mu- and delta-sites.

Acrylates↗
PubMed1992

Guanidinophenyl-substituted enol lactones as selective, mechanism-based inhibitors of trypsin-like serine proteases.

We have synthesized four guanidinophenyl-substituted protio enol and iodo enol lactones (3-(4-guanidinophenyl)-6-methylidenetetrahydro-2-pyranone (1), 3-(4-guanidinophenyl)-6-(E)-(iodomethylidene)tetrahydro-2-pyran one (2), 4-(4-guanidinophenyl)-6-methylidenetetrahydro-2-pyranone+ ++ (3), and 4-(4-guanidinophenyl)-6-(E)-(iodomethylidene)tetrahydro-2-pyran one (4)) and tested them for inhibitory activity against some trypsin-like enzymes, namely trypsin, urokinase, tissue plasminogen activator (t-PA), plasmin, and thrombin, as well as alpha-chymotrypsin and human neutrophil elastase (HNE). The beta-aryl-substituted protio lactone 3 was a potent alternate substrate inhibitor of trypsin and urokinase. The alpha-aryl-substituted iodo lactone 2 was a permanent inactivator of urokinase, plasmin, t-PA, thrombin, and alpha-chymotrypsin, exhibiting a relatively high specificity for the former two enzymes. In general, these compounds showed a preference for inactivating trypsin-like enzymes over alpha-chymotrypsin and HNE. Also, within the class of trypsin-like enzymes, there was generally good selectivity of inhibition.

Amino Acid Sequence↗
PubMed1980

Steroidal alpha-methylene delta-lactones as potential antitumor agents.

Four novel steroidal alpha-methylene delta-lactones have been synthesized and shown to be active against human nasopharyngeal carcinoma (KB) cells in culture. The syntheses involved the use of known alpha-methylenation procedures. In addition, the lactone 6 was directly methylenated by reaction with CH2O/KOH or Et2NH/CH2O/Et2NH.HCl. The formation of a cysteine adduct (15) with the alpha-methylene lactone 10 is reported.

Antineoplastic Agents↗
PubMed1975

Oxidation of furans. 3. Estrogenic properties of lactones and anhydrides derived from the oxidation of 17alpha-[3-furyl]estradiol derivatives.

The oxidation of 17alpha-[3-furyl]estradiol derivatives and the estrogenic properties of the resulting isomeric 17,21-and 17,23-dihydroxy-19,24-dinor-17alpha-chola-1,3,5(10)20(22)-tetraenoic acid(20leads to 23) gamma-lactones as well as those of the related 17-hydroxy-19-nor-17alpha-pregna-1,3,5(10)-triene-20,21-dicarboxylic acid anhydrides and gamma-lactones are described. Of these, only lactones 3c,e,h and 5b retained the same degree and profile of estrogenic activity as the starting 17alpha-[3-furyl]estradiols.

Anhydrides↗
PubMed2003

Synthetic analogues of the bacterial signal (quorum sensing) molecule N-(3-oxododecanoyl)-L-homoserine lactone as immune modulators.

Comparative immune modulatory activity for a range of synthetic analogues of a Pseudomonas aeruginosa signal molecule, N-(3-oxododecanoyl)-l-homoserine lactone (3O, C(12)-HSL), is described. Twenty-four single or combination systematic alterations of the structural components of 3O, C(12)-HSL were introduced as described. Given the already defined immunological profile of the parent compound, 3O, C(12)-HSL, these compounds were assayed for their ability to inhibit murine and human leucocyte proliferation and TNF-alpha secretion by lipopolysaccharide (LPS) stimulated human leucocytes in order to provide an initial structure-activity profile. From IC(50) values obtained with a murine splenocyte proliferation assay, it is apparent that acylated l-homoserine lactones with an 11-13 C side chain containing either a 3-oxo or a 3-hydroxy group are optimal structures for immune suppressive activity. These derivatives of 3O, C(12)-HSL with monounsaturation and/or a terminal nonpolar substituent on the side chain were also potent immune suppressive agents. However, structures lacking the homoserine lactone ring, structures lacking the l-configuration at the chiral center, and those with polar substituents were essentially devoid of activity. The ability of compounds selected from the optimal activity range to modulate mitogen-driven human peripheral blood mononuclear cell proliferation and LPS-induced TNF-alpha secretion indicates the suitability of these compounds for further investigation in relation to their molecular mechanisms of action in TNF-alpha driven immunological diseases, particularly autoimmune diseases such as psoriasis, rheumatoid arthritis, and type 1 (autoimmune) diabetes.

Adjuvants, Immunologic↗
PubMed2007

Synthesis and structure-activity relationships of new benzodioxinic lactones as potential anticancer drugs.

A set of disubstituted tetracyclic lactones has been synthesized and tested for potential antitumor activity. Several of them possess a noticeable cytotoxicity against L1210 and HT-29 colon cells in vitro. Relationships between chain nature and biological properties were sought. Lactones with a pentyl or hexyl substituent at C-11 are the most active ones. The introduction of a functional group at the side chain of C-11 modified the potency; carboxylic acid and primary amine decreased the cytotoxicity, whereas a cyano group increased the activity. An extensive structure-activity relationship study of these derivatives, including carbon homologues and bioisosteres has been performed. The synthesis and cytotoxicity of these compounds are discussed. Two lactones are recognized as potential lead compounds.

Antineoplastic Agents↗
PubMed2000

20-O-acylcamptothecin derivatives: evidence for lactone stabilization.

Convincing UV and NMR spectrophotometric evidence is presented which demonstrates that at physiological pH, 7.4, 20-O-acyl derivatives of camptothecin (CPT) are substantially more stable in the lactone form than the 20-OH parent. Additionally, it was determined by HPLC analysis that the lactone ring of a 20-O-ether derivative of CPT underwent endocyclic ring opening at pH > or =8.5, while the lactone ring of 20-O-acyl CPT derivatives remained unaffected. PEG (and other smaller alkyl) 20-O-acyl-CPT derivatives released native CPT at pH > 9.5, which arises from exocyclic cleavage, thus precluding isolation of any open CPT acyl PEG (or alkyl) carboxylate forms.

Acylation↗
PubMed2004

Interconvertions between delta-lactam and delta-lactone derivatives initiated by unique transannular interactions of the rigid cyclohexane boat structure in pentacycloundecane.

The pentacycloundecane (PCU) cage structure resembles a perfect boat conformation, and for the first time unique lactam/lactone interconversions on the flagpole carbons of a cyclohexane boat structure are reported. The syntheses of a novel dihydroxy-PCU-delta-lactone and two novel N-substituted PCU-delta-lactams are reported. Hydrolysis of some of the PCU-delta-lactam compounds produced delta-lactones, and reaction of the lactones with ammonia or primary amines again produced delta-lactams. Reaction mechanisms to account for the unusual interconversion reactions induced by transannular interactions are proposed.

Catalysis↗
PubMed2005

Regiocontrolled benzannulation of diaryl(gem-dichlorocyclopropyl)methanols for the synthesis of unsymmetrically substituted alpha-arylnaphthalenes: application to total synthesis of natural lignan lactones.

[reaction: see text] An efficient synthesis of highly substituted alpha-arylnaphthalene analogues has been developed utilizing Lewis acid-promoted regiocontrolled benzannulation of aryl(aryl')-2,2-dichlorocyclopropylmethanols (aryl not equal aryl'; abbreviated as AACMs). Both AACM diastereomers were easily prepared via highly stereoselective addition (>95/5) of ArLi to gem-dichlorocyclopropropyl aryl' ketones. The choice of Lewis acids determined the cyclization regioselectivity of the present benzannulation. TiCl4 and SnCl4 used the chelation pathway, whereas silyl triflates used a nonchelation pathway to give unsymmetrically substituted regioisomeric alpha-arylnaphthalenes in 40-91% yields with moderate to excellent regioselectivity (TiCl4 or SnCl4; >99/1-3/1, TBDMSOTf; >1/99-1/4). Thus, the alpha-aryl or alpha-aryl' moiety (accessory aryl group) was alternatively introduced to alpha-arylnaphthalenes by choosing either the order of the reaction sequences or the appropriate catalyst. Application of the present method to the total synthesis for unsymmetrically substituted natural lignan lactones, justicidin B, retrojusticidin B, dehydrodesoxypodophyllotoxin, and a related analogue, 5'-methoxyretrochinensin, was demonstrated. Lignan retrolactones (retrojusticidin B and 5'-methoxyretrochinensin) were synthesized by the conventional lactonization of the diol precursor, whereas a novel Bu2SnO-mediated monoacylation method was applied to the synthesis of normal lignan lactones (justicidin B and dehydrodesoxypodophyllotoxin).

Lactones↗
PubMed2007

Enantioselective fluorination of tert-butoxycarbonyl lactones and lactams catalyzed by chiral Pd(II)-bisphosphine complexes.

An efficient catalytic enantioselective fluorination of tert-butoxycarbonyl lactones and lactams is reported. Reactions of the lactone substrates proceeded smoothly in an alcoholic solvent with a catalytic amount of chiral Pd(II) complex. In the case of the less acidic lactam substrates, concurrent use of the Pd complex and 2,6-lutidine as a cocatalyst was effective. Under the reaction conditions, the fluorinated lactones and lactams were obtained in good yield with excellent enantioselectivity (94-99% ee).

Amines↗
PubMed2005

Density functional theory study of the hydrogen bond interaction between lactones, lactams, and methanol.

The structure and relative stability of methanol complexes with various cyclic ketones, lactones, lactams, and N-methyl lactams from three- to seven-membered rings have been investigated using the density functional theory method. The geometries, harmonic frequencies, and energies were calculated at the B3LYP/6-311+G(d,p) level. Three stable structures, cis-a, cis-b, and trans, with respect to the ring oxygen (nitrogen) atom, were found to be local minima of the potential energy surface. For lactones and N-methyl lactams, the most stable structure is trans; it is stabilized, as in cyclic ketones, through the conventional hydrogen bond (HB) interaction between the basic carbonyl oxygen and the acidic methanolic hydrogen and an unconventional HB interaction between the methanolic oxygen and the CH hydrogen, in the alpha position of the carbonyl group. For unsubstituted lactams, the cis-a structure, stabilized through a HB interaction between the NH group and the methanol oxygen in addition to the conventional HB interaction, is the most stable. The topological properties of the electron density ratify the existence of conventional (N,O-H. . .O) and unconventional (C-H. . .O) hydrogen bonding. A good correlation was found between the HB distances and the electron density at the HB critical point. The unsubstituted lactams yield more stable complexes with methanol than N-methyl lactams, lactones, and cyclic ketones. In the most stable complexes, both components behave simultaneously as a HB donor and as a HB acceptor.

Cyclization↗
PubMed2006

Sesquiterpene lactones from Inula britannica and their cytotoxic and apoptotic effects on human cancer cell lines.

Three new sesquiterpenes (1-3), together with four known sesquiterpene lactones, were isolated from the flowers of Inula britannica var. chinensis. Structures were established on the basis of high-field 1D and 2D NMR methods supported by HRMS. All sesquiterpene lactones were tested for cytotoxicity as well as apoptotic ratio in human COLO 205, HT 29, HL-60, and AGS cancer cells. Compounds 3 and 4, two alpha-methylene gamma-lactone-bearing sesquiterpenes, were modestly active in these assays.

Antineoplastic Agents, Phytogenic↗
PubMedDate not supplied

Constituents of Erysimum inconspicuum. Two sulfur-containing lactone compounds.

The alcohol extract of Erysimum inconspicuum fruits, which exhibited cytotoxic activity against the KB cell line and some activity against the P-388 lymphocytic leukemia in vivo, was studied. Strophanthidin, uzarigenin, and two sulfur-containing lactones, erysulfone[6-methylsulfonyl-4-hydroxyhexanoic acid lactone] and erysulfoxide[6-methylsulfinyl-4-hydroxyhexanoic acid lactone], were isolated and characterized by spectral data.

Antineoplastic Agents, Phytogenic↗
PubMedDate not supplied

The gastric cytoprotective effect of several sesquiterpene lactones.

The aerial part of Artemisia douglasiana, used in folk medicine as a cytoprotective agent against the development of peptic ulcer, was studied, its active principle dehydroleucodine [1] isolated, and its pharmacological properties analyzed. In order to establish whether or not the reported activity is particular to sesquiterpene lactones, the study of the cytoprotective activity of several related guaianolides and pseudoguaianolides from plants was undertaken. Ludartin [3], 8-angeloyloxy-3-hydroxyguaia-3(15),10(14),11(13)-trien-6,12- olide [4], hymenin [5], mexicanin I [6], helenanin [7], and 9-O-desacetylsparthulin-2-O-angelate [8] were found to exhibit protection. Desacetoxymatricarin [2] did not show cytoprotective activity. The results obtained from the different sesquiterpene lactones studied suggest that the presence of the alpha-methylene-gamma-lactone moiety is, in principle, a requirement for the observed antiulcerogenic activity.

Animals↗