Cytotoxic and Topographical Properties of 6-Arylidene-2-dimethylaminomethylcyclohexanone Hydrochlorides and Related Compounds

A number of 2-arylidenecyclohexanones (1a-h) were converted into the corresponding Mannich bases (2a-h) and (3a,f). Evaluation against murine L1210 cells as well as human Molt 4/C8 and CEM T-lymphocytes revealed the marked cytotoxicity of the Mannich bases and also the fact that almost invariably these compounds were more potent than the precursor enones (1a-h). Further evaluation of most of the Mannich bases towards a panel of nearly 60 human tumour cell lines confirmed their utility as potent cytotoxins. In this assay, the compounds showed growth-inhibiting properties greater than the anticancer alkylator melphalan. QSAR studies revealed that in some cell lines compounds possessing small electron-attracting aryl substituents showed the greatest potencies. Molecular modeling and X-ray crystallography demonstrated that various interatomic distances and torsion angles correlated with cytotoxicity. A representative compound (2a) demonstrated weak inhibiting properties towards human N-myristoyltransferase and stimulated a tyrosine protein kinase. A single dose of 100 mg/kg of most of the compounds did not prove to be lethal in mice.

A conformational and structure-activity relationship study of cytotoxic 3,5-bis(arylidene)-4-piperidones and related N-acryloyl analogues

A series of 3,5-bis(arylidene)-4-piperidones 1 and related N-acryloyl analogues 2 were prepared as candidate cytotoxic agents with a view to discerning those structural features which contributed to bioactivity. A number of the compounds were markedly cytotoxic toward murine P388 and L1210 leukemic cells and also to human Molt 4/C8 and CEM neoplasms. Approximately 40% of the IC50 values generated were lower than the figures obtained for melphalan. In virtually all cases, the N-acyl compounds were significantly more bioactive than the analogues 1. In general, structure-activity relationships revealed that the cytotoxicity of series 1 was correlated positively with the size of the aryl substituents, while in series 2, a -sigma relationship was established. In particular, various angles and interatomic distances were obtained by molecular modeling, and the presence of an acryloyl group on the piperidyl nitrogen atom in series 2 affected the relative locations of the two aryl rings. This observation, along with some differences in distances between various atoms in series 1 and 2, may have contributed to the disparity in cytotoxicity between 1 and 2. The results obtained by X-ray crystallography of representative compounds were mainly in accordance with the observations noted by molecular modeling. Selected compounds interfered with the biosynthesis of DNA, RNA, and protein in murine L1210 cells, while others were shown to cause apoptosis in the human Jurkat leukemic cell line. This study has revealed the potential of these molecules for development as cytotoxic and anticancer agents.

Inhibitors of abscisic acid 8'-hydroxylase

Structural analogues of the phytohormone (+)-abscisic acid (ABA) have been synthesized and tested as inhibitors of the catabolic enzyme (+)-ABA 8'-hydroxylase. Assays employed microsomes from suspension-cultured corn cells. Four of the analogues [(+)-8'-acetylene-ABA, (+)-9'-propargyl-ABA, (-)-9'-propargyl-ABA, and (+)-9'-allyl-ABA] proved to be suicide substrates of ABA 8'-hydroxylase. For each suicide substrate, inactivation required NADPH, increased with time, and was blocked by addition of the natural substrate, (+)-ABA. The most effective suicide substrate was (+)-9'-propargyl-ABA (K(I) = 0.27 microM). Several analogues were competitive inhibitors of ABA 8'-hydroxylase, of which the most effective was (+)-8'-propargyl-ABA (K(i) = 1.1 microM). Enzymes in the microsomal extracts also hydroxylated (-)-ABA at the 7'-position at a low rate. This activity was not inhibited by the suicide substrates, showing that the 7'-hydroxylation of (-)-ABA was catalyzed by a different enzyme from that which catalyzed 8'-hydroxylation of (+)-ABA. Based on the results described, a simple model for the positioning of substrates in the active site of ABA 8'-hydroxylase is proposed. In a representative physiological assay, inhibition of Arabidopsis thaliana seed germination, (+)-9'-propargyl-ABA and (+)-8'-acetylene-ABA exhibited substantially stronger hormonal activity than (+)-ABA itself.

The 1.9 A resolution structure of phospho-serine 46 HPr from Enterococcus faecalis

The histidine-containing phosphocarrier protein HPr is a central component of the phosphoenolpyruvate:sugar phosphotransferase system (PTS), which transfers metabolic carbohydrates across the cell membrane in many bacterial species. In Gram-positive bacteria, phosphorylation of HPr at conserved serine 46 (P-Ser-HPr) plays several regulatory roles within the cell; the major regulatory effect of P-Ser-HPr is its inability to act as a phosphocarrier substrate in the enzyme I reaction of the PTS. In order to investigate the structural nature of HPr regulation by phosphorylation at Ser46, the structure of the P-Ser-HPr from the Gram- positive bacterium Enterococcus faecalis has been determined. X-ray diffraction analysis of P-Ser-HPr crystals provided 10,043 unique reflections, with a 95.1 % completeness of data to 1.9 A resolution. The structure was solved using molecular replacement, with two P-Ser-HPr molecules present in the asymmetric unit. The final R-value and R(Free) are 0.178 and 0.239, respectively. The overall tertiary structure of P-Ser-HPr is that of other HPr structures. However the active site in both P-Ser-HPr molecules was found to be in the "open" conformation. Ala16 of both molecules were observed to be in a state of torsional strain, similar to that seen in the structure of the native HPr from E. faecalis. Regulatory phosphorylation at Ser46 does not induce large structural changes to the HPr molecule. The B-helix was observed to be slightly lengthened as a result of Ser46 phosphorylation. Also, the water mediated Met51-His15 interaction is maintained, again similar to that of the native E. faecalis HPr. The major structural, and thus regulatory, effect of phosphorylation at Ser46 is disruption of the hydrophobic interactions between EI and HPr, in particular the electrostatic repulsion between the phosphoryl group on Ser46 and Glu84 of EI and the prevention of a potential interaction of Met48 with a hydrophobic pocket of EI.

Sequential cytotoxicity: a theory evaluated using novel 2-[4-(3-aryl-2-propenoyloxy)phenylmethylene]cyclohexanones and related compounds

Five series of novel compounds were synthesized in order to evaluate the theory of sequential cytotoxicity which seeks to exploit the view that various cancer cells are particularly susceptible to successive attacks by cytotoxic agents. The compounds prepared were various 2-[4-(3-aryl-2-propenoyloxy)phenylmethylene]cyclohexanone s 1 and the related Mannich bases 2. In addition the analogues 3-5 lacking an olefinic bond in the ester group were also synthesized, which were predicted to be less cytotoxic than the compounds of series 1 and 2. The atomic charges at the potential sites for interaction with cellular constituents were determined by molecular modeling calculations. The biodata obtained from murine and human neoplastic cells revealed that the predictions made regarding the viability of the theory were fulfilled in approximately two-thirds of the cases indicating that further investigation of this hypothesis is warranted. In addition, the significant potencies of some of the Mannich bases toward human tumor cell lines, in particular coupled to their selective toxicity toward human leukemic and colon cancer cells, confirms their usefulness in serving as lead molecules for further development. A preliminary investigation into the mode of action of representative compounds revealed their ability to induce apoptosis and inhibit the biosyntheses of ribonucleic acid and proteins.

Phomalairdenone: a new host-selective phytotoxin from a virulent type of the blackleg fungus Phoma lingam

The chemical structure and bioactivity of phomalairdenone (7), a new sesquiterpenic host-selective phytotoxin produced by an unusual virulent type isolate of the blackleg fungus [Phoma lingam, perfect stage Leptosphaeria maculans (Desm.) Ces. et de Not.] are reported.

Crystallization and preliminary X-ray diffraction studies of monomeric isocitrate dehydrogenase from Corynebacterium glutamicum

A monomeric isocitrate dehydrogenase has been crystallized for the first time. This enzyme catalyzes the conversion of isocitrate to oxalosuccinate and subsequently to alpha-ketoglutarate and CO(2); the coenzyme NADP(+) is reduced to NADPH during the reaction. Polyethylene glycol 2000 monomethyl ether was used to crystallize the enzyme in space group C2 with unit-cell parameters a = 137.1, b = 54.6, c = 126.4 A, beta = 108.2 degrees. The very small crystal (0. 05 x 0.20 x 0.05 mm) diffracted to 3.5 A d spacing using synchrotron radiation.

The structure and some molecular properties of acetone-picrylhydrazone

Various physical measurements and quantum-mechanical computations to characterize molecular 2-propanone(2,4,6-trinitrophenyl)hydrazone, alias acetone-picrylhydrazine (AH), are reported, including an X-ray diffraction structural determination, an1H and13C NMR study of its internal hindered reorientation, and a theoretical (SCF-MO) interpretation of these observations. The structure of AH was determined by X-ray crystallography. The space group is Pbar over 1, with a = 10.1768(9) Å, b = 7.7968(18) Å, c = 8.0018(5) Å, α = 92.102(6)°, β = 99.919(7)°, γ = 105.926(6)°, Z = 2, wR2(F2) = 0.1995 based on all 2748 unique reflections. The (picryl) proton NMR thermal work yielded a Gibbs activation energy ΔG‡= 46.9 ± 0.4 kJ mol-1in acetone-d6and 48.1 ± 0.2 kJ mol-1in chloroform-d, whereas13C NMR (two pairs in the picryl ring) yielded 46.6 ± 1.0 and 46.4 ± 1.0 kJ mol-1in acetone-d6. The SCF-MO computations yielded a detailed model of the conformerization path. Various model conformations and tautomers of AH have been considered, as has removal of H+or of H0from its hydrazinic linkage.Key words: dynamic NMR, picrylhydrazone, hindered rotation, activation parameters, SCF-MO model.

Conformational and quantitative structure-activity relationship study of cytotoxic 2-arylidenebenzocycloalkanones

Various 2-arylideneindanones 1, 2-arylidenetetralones 2, and 2-arylidenebenzosuberones 3 were synthesized with the aim of determining the relative orientations of the two aryl rings which favored cytotoxicity. Molecular modeling of the unsubstituted compound in each series revealed differences in the spatial arrangements of the two aryl rings, and evaluation of these compounds against P388, L1210, Molt 4/C8, and CEM cells as well as a panel of human tumor cell lines indicated that in general the order of cytotoxicity was 3 > 2 > 1. In particular 2-(4-methoxyphenylmethylene)-1-benzosuberone (3k) had the greatest cytotoxicity, possessing 11 times the potency of the reference drug melphalan when all five screens were considered. Series 3 was considered in further detail. First, excision of the aryl ring fused to the cycloheptanone moiety in series 3 led to some 2-arylidene-1-cycloheptanones 4 which had approximately one-third of the bioactivity of the analogues 3. Second, in some screens cytotoxicity was correlated negatively with the sigma values and positively with the MR constants of the substituents in the arylidene aryl ring of 3. Third, X-ray crystallography of five representative compounds (3i,k-n) revealed differences in the locations of the aryl rings which may have contributed to the variations in cytotoxicity. Finally three members of series 3 inhibited RNA and protein syntheses and induced apoptosis in human Jurkat T cells. This study has revealed that 2-arylidene-1-benzosuberones are a group of useful cytotoxic agents, and in particular 3k serves as a prototypic molecule for subsequent structural modifications.

N,N-dimethyl-5-methoxymethyl-2'-deoxycytidine

In the title compound, C13H21N3O5, the pyrimidine ring adopts the antiperiplanar (-ap) conformation [chi = 193.54 (19) degrees]. The deoxyribose sugar ring has the C2'-exo-C3'-endo (2T3) twist conformation. The pseudo-rotational parameters of the deoxyribose sugar ring are P = 6.83 (2) degrees and Tm = 38.27 (2) degrees. The exocyclic side chain at C5' has the g+ conformation [gamma = 47.7 (3) degrees]. The 5-methoxymethyl group is distal to the deoxyribose sugar ring, with a C6-C5-C52-O52 torsion angle of -91.9 (3) degrees.

Structure of the Rhizomucor miehei aspartic proteinase complexed with the inhibitor pepstatin A at 2.7 A resolution

Crystals of Rhizomucor miehei aspartic proteinase (RMP) complexed with pepstatin A grew in the orthorhombic space group P212121 and were isomorphous to native RMP crystals. The unit-cell dimensions are a = 41.52, b = 50.82, c = 172.71 A. There is one RMP-pepstatin A complex per asymmetric unit. The structure of the RMP-pepstatin A complex has been refined to a crystallographic R value of 19.3% and an Rfree value of 28.0% at 2.7 A resolution. A pepstatin A molecule fits into the large substrate-binding cleft between the two domains of RMP in an extended conformation up to the alanine residue at the P2' position. The dipeptide analogue statine residue at the P3'-P4' position forms an inverse gamma-turn (P3'-P1') with the statine residue at the P1-P1' position and its leucyl side chain binds back into the S1' subsite. The inhibitor interacts with the residues of the substrate-binding pocket by both hydrogen bonds and hydrophobic interactions. The hydroxyl group of the statine residue at the P1-P1' position forms hydrogen bonds with both catalytic aspartate residues (Asp38 and Asp237). This conformation mimics the expected transition state of the enzyme-substrate interaction. The binding of the inhibitor to the enzyme does not produce large distortions of the active site. No domain movement was observed compared with the native enzyme structure. However, the surface-flap region (residues 82-88) undergoes a conformational change, moving toward the inhibitor and becoming rigid owing to the formation of hydrogen bonds with the inhibitor. B-factor calculations of the two domains suggest that the C-terminal domain becomes more rigid in the complex than in the native structure.

Synthesis, structure, and reactivity of macro cyclic heterobimetallic complexes of (Co, Cu), (Co, Ni), (Co, Zn), (Zn, Cu), (Zn, Ni) combinations

A series of macrocyclic heterobimetallic complexes of type [Mc(tntnam)Mo](PF6)n and [Mc'(tntnim)Ni](PF6)n where Mc = Co(III) and Zn(II), Mc' = Co(II), Co(III), and Zn(II), and Mo = Ni(II), Cu(II), and Zn(II) have been synthesized and characterized. The macrocyclic ligands tntnim 2 and tntnam 3 contain two geometrically distinct compartments, 6-coordinate (closed site) and 4-coordinate (open site), which are bridged by phenolic oxygens. The heterobimetallic complexes with Zn(II) or Ni(II) in the open site are primarily formed as 5-coordinate with a chloride ion as a fifth ligand; the latter can be removed by Ag+ ion. The crystal structures of [Zn(tntnim)NiCl]PF6·C2H5OH, 5, [Zn(tntnam)Ni](PF6)2, 11, [Zn(tntnam)Cu](PF6)2, 12, and [Co(tntnam)Ni(H2O)](PF6)3·4H2O, 14 were determined. Crystal data for 5: monoclinic, T = 123 K, a = 15.822(2), b = 15.6230(10), c = 16.432(2) Å, β = 104.570(10)°, Z = 4, space group Pc, R = 0.0371 (wR2 = 0.0843) for 5826 reflections with I [Formula: see text] 2σ(I). Crystal data for 11: tetragonal, T = 123 K, a = b = 24.122(2), c = 14.397(7) Å, Z = 8, space group P41212, R = 0.0625 (wR2 = 0.1549) for 3250 reflections with I [Formula: see text] 2σ(I). Crystal data for 12: tetragonal, T = 123 K, a = b = 24.180(2), c = 14.281(4) Å, Z = 8, space group P41212, R = 0.0588 (wR2 = 0.1219) for 3452 reflections with I [Formula: see text] 2σ(I). Crystal data for 14: triclinic, T = 287 K, a = 12.664(2), b = 12.983(2), c = 16.216(3) Å, α = 80.317(14)°, β = 69.585(12)°, γ = 74.791(12)°, Z = 2, space group P[Formula: see text], R = 0.0573 (wR2 = 0.1332) for 3443 reflections with I [Formula: see text] 2σ(I). The structures were solved by direct methods and refined by full-matrix least-squares procedures. The crystal structures demonstrate that the expected trans pyridine structures are formed. The magnetic moments, electrospray mass spectra, electronic absorption and emission spectra, and redox couples are reported. Key words: cobalt, copper, nickel, zinc, heterobimetallic, macrocycle.

4-(beta-Arylvinyl)-3-(beta-arylvinylketo)-1-ethyl-4-piperidinols and related compounds: a novel class of cytotoxic and anticancer agents

The syntheses of a series of 1-aryl-5-diethylamino-1-penten-3-one hydrochlorides 1 and 1-aryl-3-diethylamino-1-propanone hydrochlorides 4 were accomplished. Attempts to prepare the corresponding bis(5-aryl-3-oxo-4-pentenyl)ethylamine hydrochlorides 2 and bis(3-aryl-3-oxopropyl)ethylamine hydrochlorides 5 led to the formation of a series of 4-(beta-arylvinyl)-3-(beta-arylvinylketo)-1-ethyl-4-piperidi nol hydrochlorides 9 and 4-aryl-3-arylketo-1-ethyl-4-piperidinol hydrochlorides 11, most of which were converted subsequently into the corresponding quaternary ammonium salts 10 and 12, respectively. The structures of these compounds were determined by 1H NMR spectroscopy and confirmed by X-ray crystallography of representative molecules. Most compounds displayed significant cytotoxicity toward murine P388 and L1210 cells as well as human tumors. In general, Mannich bases containing olefinic bonds were more cytotoxic than the analogues without this functional group, while the piperidines 9 and 11 were more potent than the acyclic analogues 1 and 4, respectively. Correlations were noted between various physicochemical constants in the aryl rings and cytotoxicity. Compound 9d displayed promising in vivo activity against colon cancers. This study has revealed that the piperidines 9 and 11 constitute new classses of cytotoxic agents.

Cytotoxic activities of Mannich bases of chalcones and related compounds

Various Mannich bases of chalcones and related compounds displayed significant cytotoxicity toward murine P388 and L1210 leukemia cells as well as a number of human tumor cell lines. The most promising lead molecule was 21 that had the highest activity toward L1210 and human tumor cells. In addition, 21 exerted preferential toxicity to human tumor lines compared to transformed human T-lymphocytes. Other compounds of interest were 38, with a huge differential in cytotoxicity between P388 and L1210 cells, and 42, with a high therapeutic index when cytotoxicity to P388 cells and Molt 4/C8 T-lymphocytes were compared. In general, the Mannich bases were more cytotoxic than the corresponding chalcones toward L1210 but not P388 cells. A ClusCor analysis of the data obtained from the in vitro human tumor screen revealed that the mode of action of certain groups of compounds was similar. For some groups of compounds, cytotoxicity was correlated with the sigma, pi, or molar refractivity constants in the aryl ring attached to the olefinic group. In addition, the IC50 values in all three screens correlated with the redox potentials of a number of Mannich bases. X-ray crystallography and molecular modeling of representative compounds revealed various structural features which were considered to contribute to cytotoxicity. While a representative compound 15 was stable and unreactive toward glutathione (GSH) in buffer, the Mannich bases 15, 18, and 21 reacted with GSH in the presence of the pi isozyme of glutathione S-transferase, suggesting that thiol alkylation may be one mechanism by which cytotoxicity was exerted in vitro. Representative compounds were shown to be nonmutagenic in an intrachromosomal recombination assay in yeast, devoid of antimicrobial properties and possessing anticonvulsant and neurotoxic properties. Thus Mannich bases of chalcones represent a new group of cytotoxic agents of which 21 in particular serves as an useful prototypic molecule.

Importance of the Chiral Centers of Jasmonic Acid in the Responses of Plants (Activities and Antagonism between Natural and Synthetic Analogs)

The importance of the two chiral centers at C-3 and C-7 in the molecular structure of jasmonic acid in plant responses was investigated. We separated methyl jasmonate (MeJA) into (3R)- and (3S)-isomers with a fixed stereochemistry at C-3, but epimerization at C-7 is possible. The four isomers of the nonepimerizable analog 7-methyl MeJA were synthesized. These six esters and their corresponding acids were tested in three bioassays: (a) senescence in sunflower (Helianthus annuus) cotyledons; (b) proteinase inhibitor II gene expression in transgenic tobacco (Nicotiana tabacum) with [beta]-glucuronidase as a biochemical reporter; and (c) seed germination in Brassica napus and wheat (Triticum aestivum). The esters and acids had similar activities in the three assays, with the ester being more effective than its acid. The (3R)-stereochemistry was critical for jasmonate activity. Although activity was reduced after substituting the C-7 proton with a methyl group, the analogs with (3R,7R)- or (3R,7S)-stereochemistry were active in some of the assays. Although the four isomers of 7-methyl MeJA were inactive or only weakly active in the senescence assay, they could overcome the senescence-promoting effect of (3R)-MeJA. The strongest antagonistic effect was observed with the (3R,7S)-isomer.

Crystal structure of the aspartic proteinase from Rhizomucor miehei at 2.15 A resolution

The crystal structure of the aspartic proteinase from Rhizomucor miehei (RMP, EC 3. 4. 23. 23) has been refined to 2.15 A resolution to a crystallographic R-value of 0.215 and an Rfree of 0.281. The root-mean-square (r.m.s.) error for the atomic coordinates estimated from a Luzzati plot is 0.2 A. The r.m.s. deviations for the bond distances and bond angles from ideality are 0.01 A and 1.7 degrees, respectively. RMP contains two domains that consist predominantly of beta-sheets. A large substrate-binding cleft is clearly visible between the two domains, and the two catalytic residues Asp38 and Asp237 are located in the middle of the cleft with a water molecule bridging the carboxyl groups of Asp38 and Asp237. Due to crystal packing, the C-terminal domain is more mobile than the N-terminal domain. Most of the aspartic proteinases (except renin) reach their maximum activity at acidic pH. We propose that the optimum pH of each aspartic proteinase is determined by the electrostatic potential at the active site, which, in turn, is determined by the positions and orientations of all the residues near the active site. RMP is the most glycosylated among the aspartic proteinases. The carbohydrate moieties are linked to Asn79 and Asn188. Asn79 is in the middle of a beta-strand and Asn188 is on a surface loop in contrast to the previous hypothesis proposed by Brown and Yada that they are both on surface beta-turns. RMP has a very high thermal stability. The high thermal stability is probably due to the high level of glycosylation. We propose that the highly flexible carbohydrates act as heat reservoirs to stabilize the conformation of RMP and therefore give the enzyme a high level of thermal stability. Three-dimensional structural and sequence alignments of RMP with other aspartic proteinases show that RMP is most structurally homologous to that of Mucor pusillus (MPP), and differs from other fungal enzymes as much as it does from the mammalian enzymes. This suggests that RMP and MPP diverged from the main stream of aspartic proteinases at an early stage of evolution. The present study adds a second member to this subfamily of aspartic proteinases.

(Aryloxy)aryl semicarbazones and related compounds: a novel class of anticonvulsant agents possessing high activity in the maximal electroshock screen

A number of (aryloxy)aryl semicarbazones and related compounds were synthesized and evaluated for anticonvulsant activities. After intraperitoneal injection to mice, the semicarbazones were examined in the maximal electroshock (MES), subcutaneous pentylenetetrazole (scPTZ), and neurotoxicity (NT) screens. The results indicated that greater protection was obtained in the MES test than the scPTZ screen. Quantitation of approximately one-third of the compounds revealed an average protection index (PI, i.e. TD50/ED50) of approximately 9. After oral administration to rats, a number of compounds displayed significant potencies in the MES screen (ED50 of 1-5 mg/kg) accompanied by very high protection indices. In fact over half the compounds had PI figures of greater than 100, and two were in excess of 300. The compounds were essentially inactive in the scPTZ and NT screens after oral administration to rats. Various compounds displayed greater potencies and PI figures in the mouse intraperitoneal and rat oral screens than three reference clinically used drugs. The data generated supported a binding site hypothesis. Quantitative structure-activity relationships indicated a number of physicochemical parameters which contributed to activity in the MES screen. X-ray crystallography of five compounds suggested the importance of certain interatomic distances and bond angles for activity in the mouse and rat MES screens.

Mutation of serine-46 to aspartate in the histidine-containing protein of Escherichia coli mimics the inactivation by phosphorylation of serine-46 in HPrs from gram-positive bacteria

Histidine-containing protein (HPr) is a phosphocarrier protein of the bacterial phosphoenolpyruvate:sugar phosphotransferase system. HPr is phosphorylated at the active site residue, His15, by phosphoenolpyruvate-dependent enzyme I in the first enzyme reaction in the process of phosphoryl transfer to sugar. In many Gram-positive bacterial species HPr may also be phosphorylated at Ser46 by an ATP-dependent protein kinase but not in the Gram-negative Escherichia coli and Salmonella typhimurium. One effect of the phosphorylation at Ser46 is to make HPr a poor acceptor for phosphorylation at His15. In Bacillus subtilis HPr, the mutation Ser46Asp mimics the effects of phosphorylation. A series of mutations were made at Ser46 in E. coli HPr: Ala, Arg, Asn, Asp, Glu, and Gly. The two acidic replacements mimic the effects of phosphorylation of Ser46 in HPrs from Gram-positive bacteria. In particular, when mutated to Asp46, the His 15 phosphoacceptor activity (enzyme I Km/Kcat) decreases by about 2000-fold (enzyme I Km, 4 mM HPr; Kcat, approximately 30%). The alanine and glycine mutations had near-wild-type properties, and the asparagine and arginine mutations yielded small changes to the Km values. The crystallographic tertiary structure of Ser46Asp HPr has been determined at 1.5 A resolution, and several changes have been observed which appear to be the effect of the mutation. There is a tightening of helix B, which is demonstrated by a consistent shortening of hydrogen bond lengths throughout the helix as compared to the wild-type structure. There is a repositioning of the Gly54 residue to adopt a 3(10) helical pattern which is not present in the wild-type HPr. In addition, the higher resolution of the mutant structure allows for a more definitive placement of the carbonyl of Pro11. The consequence of this change is that there is no torsion angle strain at residue 16. This result suggests that there is no active site torsion angle strain in wild-type E. coli HPr. The lack of substantial change at the active center of E. coli HPr Ser46Asp HPr suggests that the effect of the Ser46 phosphorylation in HPrs from Gram-positive bacteria is due to an electrostatic interference with enzyme I binding.

Structural modifications of the primary amino group of anticonvulsant aryl semicarbazones

A number of aryl semicarbazones had been shown previously to possess significant anticonvulsant properties. The principal objective of the present investigation was to determine the importance of the primary amino group in this series of compounds by replacing it with other substituents. The results indicate that the amino group was not essential for anticonvulsant activity. However its replacement by an aryl ring generally abolished activity while a terminal phenylamino function was better tolerated. Thus both the size of the group and its hydrogen bonding capabilities appear to influence bioactivity. Alteration of the oxygen atom of the semicarbazones by isosteres did not enhance anticonvulsant properties.

Synthesis and cytotoxic evaluation of mesna adducts of some 1-aryl-4,4-dimethyl-5-(1-piperidino)-1-penten-3-one hydrochlorides

Reaction of 1-(4-bromophenyl)-4,4-dimethyl-5-(1-piperidino)-1-penten-3-one hydrochloride (1f) with sodium 2-mercaptoethanesulphonate (mesna) gave rise to the thiol adduct. 3. Recrystallization of this compound led to the formation of the corresponding zwitterion 4f. A series of analogues of 4f were prepared and the structure of a representative compound was confirmed by X-ray crystallography. In general, the thiol adducts had similar activity towards P388 cells and human tumour cell lines as the precursor enones 1 although greater selectivity to malignant diseases was found with the thiol adducts. A stability study of representative compounds conducted by 1H NMR spectroscopy revealed that the thiol adducts decomposed in solution. In one case regeneration of the ketone was noted while for the other compounds, the decomposition products were not identified.

Crystallization and preliminary X-ray structure solution ofRhizomucor mieheiaspartic proteinase

Rhizomucor miehei aspartic proteinase (M(r) = 38701, 361 residues) has been crystallized in a form suitable for analysis by X-ray diffraction. The flattened rod-shaped crystals were grown from polyethylene glycol 8000 using vapour-diffusion methods. The crystal form is in space group P2(1)2()12(1) [a = 41.67 (2), b = 51.21 (3) and c = 173.3 (2) A], with Z = 4 and one molecule in the asymmetric unit. Data were collected over the range 0 < h < 14, 0 < k < 16 and 0 < l < 62, resulting in 7032 unique reflections to give 72.1% completeness with a merging R of 0.067 to a resolution limit of 2.8 A. A molecular-replacement solution of the structure has been obtained using the aspartic proteinase from Rhizomucor pusillus as a model. Rigid-body refinement of the model and subsequent refinement using molecular dynamics were performed with X-PLOR, leading to a current R-factor of 20.1% for 2.8 A data.

Trifluoperazine-induced conformational change in Ca(2+)-calmodulin

Here we show that, as a consequence of binding the drug trifluoperazine, a major conformational movement occurs in Ca(2+)-calmodulin (CaM). The tertiary structure changes from an elongated dumb-bell, with exposed hydrophobic surfaces, to a compact globular form which can no longer interact with its target enzymes. It is likely that inactivation of Ca(2+)-CaM by trifluoperazine is due to this major tertiary-structural alteration in Ca(2+)-CaM, which is initiated and stabilized by drug binding. This conformational change is similar to that which occurs on the binding of Ca(2+)-CaM to target peptides. Two hydrophobic binding pockets, created by amino acid residues adjacent to Ca(2+)-coordinating residues, form the key recognition sites on Ca(2+)-CaM for both inhibitors and target enzymes.

Cytotoxic evaluation of some 3,5-diarylidene-4-piperidones and various related quaternary ammonium compounds and analogs

A number of 3,5-diarylidene-4-piperidones (1) and some related quaternary ammonium salts (5) as well as closely related analogs were prepared principally as candidate cytotoxic agents in two screens. The first test system used an average of 54 human tumor cell lines from eight neoplastic diseases, namely leukemia, melanoma, colon, non-small-cell lung, small-cell lung, central nervous system, ovarian, and renal cancers. Selective toxicity was demonstrated by some of the compounds, especially toward leukemia. The second screen used L1210 lymphoid leukemia cells. In general, the compounds were less cytotoxic than the reference drug melphalan in both screens. Linear plots were made between the Hammett (sigma), fragment (f), and molar refractivity (MR) constants of the nuclear substituents in series 1 and 5 with the IC50 figures of both the human tumor cell lines and L1210 cells. Evaluation against the human tumor cell lines revealed that increases in the f values were correlated with elevation of cytotoxicity in both series 1 and 5; MR constants were also important in series 5. In the L1210 screen, sigma and MR constants were positively correlated with cytotoxicity. X-ray crystallography was undertaken on 3,5-bis-[[4'-(methylthio)phenyl]methylene]-1-methyl-4-piperidone methiodide (5d), which had significant cytotoxicity, and 3,5-bis(4-pyridylmethylene)-1-methyl-4-piperidone methiodide (6), which was virtually inactive in both screens.(ABSTRACT TRUNCATED AT 250 WORDS)

Synthesis and cytotoxic evaluation of some cyclic arylidene ketones and related oximes, oxime esters, and analogs

A number of arylidene derivatives of alicyclic ketones and some corresponding oximes, oxime esters, and related compounds were prepared as candidate cytotoxic agents. All of the compounds were evaluated against murine L1210 lymphoid leukemia cells. In general, cytotoxicity was greatest with the alpha,beta-unsaturated ketones and diminished with the oximes, and the oxime esters had little or no activity in this screen. When the same compounds were examined in both the in vitro L1210 and P388 leukemia screens, in the majority of cases the L1210 cells were more sensitive to these derivatives. Over half of the compounds prepared were evaluated against approximately 55 human tumors in vitro and showed selective toxicity toward one or more groups of neoplastic diseases, particularly leukemia. Some correlations between structure and bioactivity were discerned. The cytotoxicity screening and stability studies of representative compounds suggested that the ketones, oximes, and oxime esters were stable under the conditions of bioevaluation. X-ray crystallography of four representative compounds revealed structural features associated with cytotoxicity which may be considered in the design of future candidate cytotoxins.

Structural comparison of the histidine-containing phosphocarrier protein HPr

The phosphocarrier protein HPr is a central component of the bacterial phosphoenolpyruvate:sugar phosphotransferase system (PTS) that is responsible for carbohydrate uptake in many bacterial species. A number of three-dimensional structures of HPrs from both Gram-positive and Gram-negative bacteria have been determined; the overall folding topology of HPr is an open-faced beta-sandwich composed of three alpha-helices and a beta-sheet. A detailed structural comparison of these HPrs has been carried out. Besides the overall main chain folding, many detailed structural features are well conserved in all HPr structures. The three x-ray structures of HPrs from Escherichia coli, Streptococcus faecalis, and Bacillus subtilis show considerable overall similarity with respect to the positions of the C alpha atoms. A significant structural difference between HPrs from Gram-positive and Gram-negative bacteria is found in the region of Gly54, owing to the steric effects of Tyr37 in HPrs from the Gram-positive species. The region around Gly54 is involved in the binding of HPr to other PTS proteins and the differences in this region may be responsible for some of the poor functional complementation between HPrs from Gram-positive and Gram-negative species. The active center region, residues 12-18, appears to have significant differences in the comparisons between the overall structures. These differences support the proposal that phosphorylation and dephosphorylation of the active site His15 is accompanied by conformational changes. However, a local structural comparison of residues 12-18 from the x-ray structures of HPrs from E. coli and B. subtilis, and the two-dimensional nuclear magnetic resonance structure of B. subtilis HPr suggests that there is a conserved active center involving residues His15, Arg 17, and Pro18, which shows little conformational change during the phosphorylation cycle. The results of other experimental approaches, including site-directed mutagenesis and NMR spectroscopy, are in some cases difficult to rationalize with some of the details of the structures, but do appear to favour the conclusion that little conformational change occurs.

The 1.6 A structure of histidine-containing phosphotransfer protein HPr from Streptococcus faecalis

The histidine-containing phosphocarrier protein (HPr) is a central component of the phosphoenolpyruvate: sugar phosphotransferase system (PTS) that transports carbohydrates across the cell membrane of bacteria. The three-dimensional structure of Gram-positive Streptococcus faecalis HPr has been determined using the method of multiple isomorphous replacement. The R factor for all data is 0.156 for S. faecalis HPr at 1.6 A resolution with very good geometry. The overall folding topology of HPr is a classical open-faced beta-sandwich, consisting of four antiparallel beta-strands and three alpha-helices. Remarkable disallowed Ramachandran torsion angles of Ala16 at the active center, revealed by the X-ray structure of S. faecalis HPr, demonstrate a unique example of torsion-angle strain that is likely involved directly in protein function. A brief report concerning the torsion-angle strain has been presented recently. A newly-determined pH 7.0 structure is shown to have the same open conformation of the active center and the same torsion-angle strain at Ala16, suggesting that pH is not responsible for the structural observations. The current structure suggests a role for residues 12 and 51 in HPr's function, since they are involved in the active center through direct and indirect hydrogen-bonding interactions with the imidazole ring of His15. It is found that Ser46, the regulatory site in HPr from Gram-positive bacteria, N-caps the minor alpha-B helix and is also involved in the Asn43-Ser46 beta-turn. This finding, in conjunction with the proposed routes of communication between the regulatory site Ser46 and the active center in S. faecalis HPr, provides new insight into the understanding of how Ser46 might function. The putative involvement of the C-terminal alpha-carboxyl group and the related Gly67-Glu70 reverse beta-turn with respect to the function of HPr are described.

The 2.0-A resolution structure of Escherichia coli histidine-containing phosphocarrier protein HPr. A redetermination

The x-ray structure of Escherichia coli HPr has been redetermined at 2.0-A resolution. In contrast to the previous study (El-Kabbani, O. A. L., Waygood, E. B., and Delbaere, L. T. J. (1987) J. Biol. Chem. 262, 12926-12929), the overall structure is, in general, similar to other reported NMR and x-ray HPr structures, although there are some important differences in detail. The overall folding topology of HPr is a classical open-faced beta-sandwich, consisting of four antiparallel beta-strands and three alpha-helices. The least square refinement produced an R index of 0.135 for all measured unique data between 8.0 and 2.0 A resolution. The active center consists of His15 which is hydrogen bonded to a sulfate anion, and Arg17 which has a fully open conformation. This corresponds to the first observed "semi-closed" conformation of the active center of HPr. The Streptococcus faecalis HPr structure (Jia, Z., Vandonselaar, M., Quail, J. W., and Delbaere, L. T. J. (1993) Nature 361, 94-97) has the "open" conformation in which the side chains of His15 and Arg17 are directed as far away from each other as possible. The Bacillus subtilis HPr (Herzberg, O., Reddy, P., Sutrina, S., Saier, M. H., Jr., Reizer, J., and Kapadia, G. (1992) Proc. Natl. Acad. Sci. U.S.A. 89, 2499-2503) has the "closed" conformation in which the side chains of His15 and Arg17 are close together with a sulfate anion located in the active center. The open conformation represents the unphosphorylated form of HPr whereas the closed conformation likely resembles the phosphorylated form of HPr. The semi-closed conformation observed in the E. coli HPr structure could represent a structural intermediate on the phosphorylation/dephosphorylation pathway of HPr.

Anticonvulsant activities of some arylsemicarbazones displaying potent oral activity in the maximal electroshock screen in rats accompanied by high protection indices

Various semicarbazones derived from aryl aldehydes, phenylalkyl aldehydes, and phenylalkyl ketones as well as some related compounds were evaluated for anticonvulsant activity. Most of the compounds displayed anticonvulsant activity in the maximal electroshock (MES) and subcutaneous pentylenetetrazole (scPTZ) screens accompanied by neurotoxicity when given to mice by the intraperitoneal route. However quantitative data revealed protection indices (TD50/ED50) of less than 4 in general. Oral administration of the compounds to rats led to excellent potency in the MES screen accompanied by high protection indices while virtually no activity in the scPTZ test was displayed. These observations support the theory that one large hydrophobic group (in this case the aryl ring) and two electron donor atoms (present in the semicarbazono group) are requirements for protection in the MES screen. In general, the semicarbazones had rapid onsets of action, and one of the ways in which these compounds displayed their anticonvulsant activity is likely to be interaction with chloride channels. Empirical and semiempirical conformational calculations indicated that certain molecular fragments and hydrophobicity of these molecules affect bioactivity.

Evaluation of mutagenesis for epitope mapping. Structure of an antibody-protein antigen complex

The location and description of epitopes on proteins describe the basis of immunological specificity. The 2.8-A structure of the phosphocarrier protein, HPr from Escherichia coli, complexed to the Fab fragment of the monoclonal antibody, Jel42, has been determined. This allows the first comparison of epitope predictions from extensive site-directed mutagenesis experiments, coupled with biological activity studies (Sharma, S., Georges, F., Klevit, R. E., Delbaere, L. T. J., Lee, J. S., and Waygood, E. B. (1991) Proc. Natl. Acad. Sci. U.S.A. 88, 4877-4881), with those from x-ray analysis. There are 14 amino acid residues of E. coli HPr that interact with the Jel42 antigen-binding site. Nine of these were correctly assigned by the mutagenesis studies. Of the 5 remaining residues, Met-1 could not be altered; two others appear to have critical roles in determining protein conformation; the other 2 residues have a minimal effect on antibody binding since they are located on the periphery of the epitope with one face of their side chains in van der Waals contact with the antibody and the other face in contact with solvent. Four residues were incorrectly assigned to the epitope. These residues were located adjacent to epitope residues that were likely perturbed by these mutations. This study demonstrates that mutations which caused greater than 10-fold changes in antibody binding affinity were correctly assigned to the epitope by the mutagenesis experiments. Guidelines are also presented in order to minimize incorrect assignments.