6-[(aminoalkyl)amino]-substituted 7H-benzo[e]perimidin-7-ones as novel antineoplastic agents. Synthesis and biological evaluation

A class of chromophore-modified anthracenediones with an additional pyrimidine ring incorporated into the chromophore system has been obtained in an attempt to provide compounds with diminished peroxidation activity and thus potentially lowered cardiotoxicity. Their synthesis was carried out by the reaction of 6-amino- or 6-hydroxy-7H-benzo[e]perimidin-7-one with a number of alkylamines. Potent activity was demonstrated in vitro against murine L1210 leukemia cells (equipotent with ametantrone) as well as against P388 leukemia in vivo (% T/C = 130-255). We observed that the benzoperimidines did not stimulate free radical formation, perhaps due to their poor substrate properties for NADH dehydrogenase.

A theoretical study of the mechanism of oxygen binding by model anthraquinones. I: Quantum mechanical evaluation of the oxygen-binding sites of 1,4-hydroquinone

The undesirable cardiotoxicity of some important classes of antitumor drugs, such as anthracycline derivatives, is caused by their mediation of the one-electron reduction processes of the oxygen molecule which produces the highly toxic superoxide anion radical. Recent studies enable the conclusion to be drawn that the first and rate-limiting stage of this process is the formation of complexes of the drug anthraquinone moiety with 1 delta g molecular oxygen. The complexes can easily undergo one-electron reduction, whose product dissociates into the unchanged drug molecule and the superoxide anion radical. The present study reports quantum mechanical calculations of the structure and the energies of the possible oxygen complexes of the most simplified model compound: 1,4-benzenediol (1,4-hydroquinone); 2,3-dihydro-2,3-epidioxy-, 2,5-dihydro-2,5-epidioxy- and 1,4-epidioxy-1,4-benzenediol (the 2,3-, 2,5- and 1,4-peroxide). Calculations were carried out with the use of ab initio (STO-3G, 4-31G, and 6-31G) and semiempirical MNDO methods with total geometry optimization. The optimized geometry parameters were found to be in a reasonable agreement with the available crystal data. During the oxygen complex formation with hydroquinone, charge transfer occurs from hydroquinone to the oxygen molecule. Supplementary MNDO calculations have shown that the stability of 2,3-peroxide is increased substantially upon the ionization of one of the hydroxyl groups of hydroquinone prior to oxygen binding, which increases the electron density of the benzene ring. These findings result in a prediction that the anthracycline derivatives with electron-withdrawing substituents in the II-electron moiety should exhibit diminished affinity towards oxygen and, consequently, diminished ability to peroxidation. It has also been found that the relative energies of different peroxides are well represented even in the STO-3G ab initio calculations which will enable the further extension of the study to the complete II-electron moiety of the actual anthracycline derivatives.

Investigation of the inhibition pathway of glucosamine synthase by N3-(4-methoxyfumaroyl)-L-2,3-diaminopropanoic acid by semiempirical quantum mechanical and molecular mechanics methods

Glucosamine synthase (E.C. 2.6.1.16) is a promising target in antifungal drug design. It has been reported that its potent inhibitor, N3-(4-methoxyfumaroyl)-L-2,3-diaminopropanoic acid (FMDP), inactivates the enzyme by the Michael addition of the S-H group to the FMDP molecule followed by cyclisation reactions. In this study we have investigated, by means of semiempirical MNDO, PM3 and molecular mechanics methods, the energetics and kinetic possibility of the formation of various stereoisomers of the products of cyclisation of the Michael addition products detected experimentally. It was found that the substituted 1,4-thiazin-3-one can be formed in one step under alkaline conditions; the stereoisomers of this compound predicted to be the most stable on the basis of theoretical calculations are also the dominant ones in reality.

The essential role of anthraquinones as substrates for NADH dehydrogenase in their redox cycling activity

Redox potential, superoxide production and NADH dehydrogenase substrate properties of daunorubicin, its four sugar-modified derivatives, 4-demethoxydaunorubicin and ametantrone have been examined. A new method for the determination of substrate properties of anthraquinones for NADH dehydrogenase has been developed. This method is based on the ability of anthraquinones to decrease the amount of enzymatic cytochrome c reduction at low concentrations of NADH. The compounds examined stimulated oxygen radical formation in a very varied manner. However, they had very similar redox properties. On the other hand, the extent of the diminution of cytochrome c reduction by anthraquinones depended strongly on the structure of the compounds examined. We postulate that it is not the redox properties but the enzyme substrate properties of anthraquinones which play the most important role in stimulating free radical formation.

A theoretical study of glucosamine synthase. II. Combined quantum and molecular mechanics simulation of sulfhydryl attack on the carboxyamide group

Continuing our theoretical studies of glucosamine synthase catalysis, we have carried out MNDO and ab initio calculations of the first stage of the reaction, which involves the attack of a cysteine thiol group from the enzyme active site on the side chain carboxyamide group of glutamine, producing ammonia and thioester. The reactants were modelled by methyl mercaptate and acetamide, respectively. For two considered mechanisms of the reaction the energy surfaces were evaluated. Mechanism I, proposed by Chmara et al. (1985) involves the nucleophilic attack of a deprotonated thiol group on the carbonyl carbon atom. Mechanism II, postulated in our previous work (Tempczyk et al. 1989), assumes the concerted binding of the mercaptate sulphur to the carbonyl carbon and the sulfhydryl hydrogen to the amide nitrogen with simultaneous breaking of the S-H bond. The energy surface of mechanism I shows no minimum on the approach of the mercaptide anion towards the carbonyl carbon, which is also consistent with ab initio calculations in a 4-31 G basis set. Therefore, mechanism I seems to be unlikely. The same analysis of mechanism II shows that it leads to the desired products: methyl thioacetate and ammonia. The presence of a sulfhydryl hydrogen causes apparent pyramidicity of the amido nitrogen and lengthening of the C-N bond in the transition state, making conditions for the release of the ammonia molecule. The MNDO calculated energy barrier of the reaction is 50.1 kcal/mol and the approximate 4-31 G ab initio barrier (at the MNDO geometries of the substrate complex and the transition state) is 63 kcal/mol.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of serum proteins on biological activity of anticandidal peptides containing N3-(4-methoxyfumaroyl)-L-2,3-diaminopropanoic acid

The binding of several anticandidal peptides containing N3-(4-methoxyfumaroyl)-L-2,3-diaminopropanoic acid (FMDP) to serum proteins was studied using equilibrium dialysis. The affinity of these FMDP-peptides for serum albumin was low and well correlated with their biological activity against Candica albicans ATCC 26278 in serum albumin solution. This binding did not affect the biological activity of FMDP-peptides. On the other hand, substantial raising of MIC values was observed when anticandidal activity of FMDP peptides was assayed in the presence of complete serum proteins. This effect was likely to be a result of interaction with non-albumin components of serum proteins. Preliminary evidence points to the possibility of non-specific interaction with components containing sulfhydryl groups. In this study Nva-FMDP-Nva peptide was shown to be the most active compound in the serum protein solution. Moreover Nva-FMDP-Nva was most resistant to inactivation by serum components in comparison to other FMDP-peptides.

N3-haloacetyl derivatives of L-2,3-diaminopropanoic acid: novel inactivators of glucosamine-6-phosphate synthase

N3-Haloacetyl derivatives of L-2,3-diaminopropanoic acid, novel glutamine analogs, were shown to be strong inhibitors of glucosamine-6-phosphate synthase from bacteria and Candida albicans. The inhibition was competitive with respect to glutamine and non-competitive with respect to D-fructose-6-phosphate. In the absence of glutamine, the tested compounds inactivated glucosamine-6-phosphate synthase from C. albicans with Kinact = 0.5 microM, 0.55 microM and 18.5 microM for bromoacetyl-, iodoacetyl- and chloroacetyl derivatives of L-2,3-diaminopropanoic acid, respectively. The inactivation obeyed the criteria for active site-directed modification.

Molecular determinants of singlet oxygen binding by anthraquinones in relation to their redox cycling activity

A series of model anthraquinones with varying symmetry of pi-electron density distribution have been examined to verify our previous hypothesis concerning the essential role of quinone-singlet oxygen complex formation by asymmetric anthraquinones in their peroxidating properties. Comparison of the results of enzymatic studies using NADH dehydrogenase with those of cyclovoltammetric measurements fully confirmed the assumption that one-electron transfer mediation is facilitated by the preceding quinone-oxygen complex formation. To extend the scope of the molecular determinants of oxygen binding found in our previous studies, CNDO/2 and molecular electrostatic field (MEF) calculations have been performed. It has been concluded that the analysis of molecular electrostatic field as well as the dipole moment components has to be taken into account to judge whether a mutual orientation of the quinone and oxygen molecule can be reached which enables binding to occur. The second important factor is the appropriate symmetry of the quinone outer filled orbitals which assures that binding is not forbidden by the Woodward-Hoffman rules. These characteristics also explain the lack of oxygen binding by some asymmetric anthraquinones. The efficient electron transfer mediation be anthraquinones requires, beside the formation of the intermediate quinone-oxygen complex, effective catalysis of this process by oxidoreductase enzyme. The results obtained with model anthraquinones indicated that compounds with more than one phenolic group and an unsubstituted quinone carbonyl are good NADH dehydrogenase substrates. Imino derivatives and compounds with a reduced number or without free phenolic groups exhibit low affinity towards the enzyme.

Synergistic action of nikkomycin X/Z with azole antifungals on Candida albicans

Fluconazole, ketoconazole and tioconazole were shown to act synergistically in vitro with the antibiotic nikkomycin X/Z on the pathogenic fungus Candida albicans. The phenomenon was demonstrated using a checkerboard technique and growth inhibition experiments. The azole antifungal agents, even at concentrations not affecting growth, decreased the incorporation of the 14C-label from [14C]glucose into chitin of the candidal cell wall. After 3 h incubation with tioconazole, 1 microgram ml-1, the incorporation of the radiolabelled glucose into chitin of intact cells and regenerating spheroplasts of C. albicans was inhibited by 43% and 30%, respectively. Moreover, the relative chitin content was approximately 45% lower than that of control cells. The chitin content increased after prolonged incubation with azoles, thus confirming the known phenomenon of azole-induced uncoordinated chitin synthesis and deposition. On the other hand, azole derivatives had very little effect on the rate of nikkomycin transport into C. albicans cells. A sequential blockade mechanism of synergism is proposed.

Bacteriolytic effect of teicoplanin

The glycopeptide antibiotic teicoplanin belongs to the same group as vancomycin and ristocetin and is a valuable tool for studying the autolytic system of sensitive Gram-positive bacteria. Teicoplanin, at a concentration of 1 microgram ml-1, caused rapid lysis of exponential phase cells of Streptococcus faecalis. Bacillus spp. were most sensitive to the antibiotic; effective lysis occurred at 0.1 microgram teicoplanin ml-1. The bacteriolytic effect depended on the antibiotic concentration, the growth phase and growth rate of the target organism. Antibiotic added to overnight cultures did not cause lysis. Mg2+ (50 mM) was unable to prevent lysis. Mutants with decreased autolytic activity were more resistant to teicoplanin and lysed more slowly than the wild-type. Growth of bacteria in slightly acidic medium protected the cells against the lytic effect of teicoplanin typically observed at pH 7 or 8. This pH-dependent antibiotic tolerance was demonstrated with both bacilli and streptococci. Bacterial lysis was prevented by the presence of Ac-L-Lys(Ac)-D-Ala-D-Ala and normal growth was observed when this peptide was added simultaneously with teicoplanin. Bacteria pretreated with teicoplanin, washed and transferred to fresh medium or buffers behaved as if the antibiotic was still present; in neutral or slightly alkaline conditions strong lysis occurred, whereas in acidic buffer only bacteriostasis was observed. In contrast to vancomycin, teicoplanin induced some lysis of bacteria in hypertonic media, presumably by affecting the integrity of the cell membrane.

Synthesis, peroxidating ability, and antineoplastic evaluation of 1-[(aminoalkyl)amino]-4-hydroxy-10-imino-9-anthracenones

A novel group of cytotoxic anthraquinone derivatives, 1-[(aminoalkyl)amino]-4-hydroxy-10-imino-9-anthracenones, has been synthesized. It has been shown that imino analogues of the anthracenediones exhibit diminished ability to generate oxygen radicals. The cytotoxic activity of iminoanthracenones obtained was lower than that of the related quinone carbonyl analogues. One of the obtained imino compounds showed a moderate antileukemic activity in vivo.

Mechanism of action of anticandidal dipeptides containing inhibitors of glucosamine-6-phosphate synthase

The mechanism of anticandidal action of novel synthetic dipeptides containing N3-(4-methoxyfumaroyl)-L-2,3-diaminopropanoic acid (FMDP) residues was shown to be consistent with the "warhead delivery" concept. FMDP dipeptides were shown to be transported into Candida albicans cells by the di-tripeptide permease and subsequently hydrolyzed by intracellular peptidases, especially aminopeptidase. The anticandidal activity of the particular FMDP dipeptide was influenced by the rate of its transport and, to a lower extent, by the intracellular cleavage rate. A high transport rate accompanied by a high cleavage rate resulted in the high anticandidal activity of L-norvalyl-FMDP. The strong growth-inhibitory effect of this compound was the consequence of inhibition of the enzyme glucosamine-6-phosphate synthase by the released FMDP. The action of L-norvalyl-FMDP on exponentially growing C. albicans cells resulted in a sharp decrease of incorporation of 14C label from [14C]glucose into chitin, mannoprotein, and glucan. This effect, as well as the growth-inhibitory effect, was fully reversed by exogenous N-acetyl-D-glucosamine. Glucosamine-6-phosphate synthase was proved to be the only essential target for FMDP dipeptides. Scanning electron microscopy of C. albicans cells treated with L-norvalyl-FMDP revealed highly distorted, wrinkled, and collapsed forms. Cells formed long, bulbous chains, and partial lysis occurred.

Antimicrobial properties of N3-(iodoacetyl)-L-2,3-diaminopropanoic acid-peptide conjugates

Six peptide conjugates consisting of either norvaline, methionine, or lysine and N3-(iodoacetyl)-L-2,3-diaminopropanoic acid--a strong, irreversible inactivator of bacterial and fungal glucosamine-6-phosphate synthase--were synthesized and their antibacterial and antifungal activities were evaluated. Antimicrobial potencies of these peptides were correlated with their transport and cleavage rates inside the cells. Bacteriolysis of Bacillus pumilus cells and inhibition of [14C]glucose incorporation into cell-wall polysaccharides of Candida albicans as a result of glucosamine 6-phosphate inactivation were also observed. Reversal of growth inhibitory effect of these peptides by N-acetylglucosamine in bacteria and fungi suggests the effective delivery of N3-iodoacetyl-L-2,3-diaminopropanoic acid into the cell by a peptide-transport system.

Amphotericin B O-methyl oxime. Synthesis and biological properties

Synthesis and biological properties of amphotericin B O-methyl oxime are described. The presence of an intact hemiketal ring in the antibiotic molecule appeared to be essential for its biological activity.

Kinetic study of interaction between [14C]amphotericin B derivatives and human erythrocytes: relationship between binding and induced K+ leak

The relationship between polyene antibiotic binding to red cells and their membrane permeabilization was studied using two 14C-labelled amphotericin B (AmB) derivatives: N-fructosyl AmB and N-acetyl methyl ester AmB. The binding kinetics of both derivatives were determined on whole red cells and ghosts. The resulting experimental points were well fitted by monoexponential functions, and the characteristic t1/2 for both derivatives were calculated from these functions. At 2 X 10(-5) M, the half time t1/2 for N-acetyl methyl ester AmB (30.2 min) which forms aqueous aggregates was longer than the t1/2 for the more soluble species N-fructosyl AmB (4.5 min). At lower concentrations (10(-7) M), the t1/2 for N-acetyl methyl ester AmB (6.3 min) in a more solubilized form was close to that of N-fructosyl AmB (7.9 min). These results suggest that only solubilized species bound to red cell membranes and that disaggregation of aggregates is the limiting step in the binding process. The permeabilization of red cell membranes by N-fructosyl AmB, measured as intracellular K+ leak, was not instantaneous and at 10 degrees C external K+ was only detected 20 min after antibiotic addition. In contrast, binding occurs without lag time. Consequently, different mecanisms underlie binding and K+ permeability inducement. Absorption spectroscopy data showed that bound antibiotic is located in the hydrophobic membrane interior and that this penetration of the membrane by AmB derivatives occurs without lag time. Consequently, the lag time occurring for K+ permeability inducement would be due to some steps subsequent to binding and probably located in the hydrophobic membrane interior. This statement is further supported by the observation that the lag time is sensitive to changes in membrane fluidity as shown here by the break between 20 and 30 degrees C in the slope of the Arrhenius plot for the lag time, coinciding with the phase transition in red cell membranes.

Enzymatic studies of the effect of Cu (II) on oxygen radical production stimulated by daunorubicin and ametantrone

Daunorubicin can bind Cu (II) in Tris-HCl buffer (pH 7.4) and in the presence of NADH (100 microM). The complex is very stable. Cu (II) is not removed from the complex by cytochrome c reductase. The complexation of Cu (II) to daunorubicin gives rise to a modification of its redox properties. The complex, unlike the free drug, does not stimulate oxygen radical production. Ametantrone can also form a complex with Cu (II) in the conditions of enzymatic assays. Nevertheless, this complex is not stable in the presence of cytochrome c reductase. It dissociates immediately after the addition of the enzyme with releasing the metal ion.

Influence of net charge on the aggregation and solubility behaviour of amphotericin B and its derivatives in aqueous media

The poor solubility of polyene antibiotics in aqueous media limits their application in the therapy of systemic fungal infections. In the present paper we have demonstrated that the ionic state (net electrical charge) of the antibiotic molecule is an important factor in determining the aggregation and solubility properties of amphotericin B and its derivatives. A multi-step model of polyene self-association in aqueous media has been proposed as an explanation for the fact that some major differences are observed when aggregation is monitored by different techniques.

Anticandidal properties of N3-(4-methoxyfumaroyl)-L-2,3-diaminopropanoic acid oligopeptides

Tri-, tetra-, and pentapeptides containing N3-(4-methoxyfumaroyl)-L-2,3-diaminopropanoic acid (FMDP), an inactivator of glucosamine 6-phosphate synthase of fungal origin (a key enzyme in the biosynthesis of macromolecular components of the fungal cell wall) have been synthesized and investigated as anticandidal agents. Structure-activity relationships of a series of peptides revealed that tripeptides were generally more active than the other peptides examined. In this study, the lysyl peptide, Lys-Nva-FMDP has been found to be the most active compound in the series.

The structure of vacidin A, an aromatic heptaene macrolide antibiotic. II. Stereochemistry of the antibiotic

On the basis of coupling constants and rotating frame nuclear Overhauser effect spectroscopy of vacidin A methoxycarbonylmethylamide, the stereochemistry of the antibiotic was established. The configuration of the aglycone was determined as (3R,7R,9R,11S,13S,15R,17S,18R,19S,21R, 36S,37R,38S). The aminosugar constituent of the antibiotic was identified as beta-(D)-mycosamine. The chiral center at C-41 remains to be assigned.

The structure of vacidin A, an aromatic heptaene macrolide antibiotic. I. Complete assignment of the 1H NMR spectrum and geometry of the polyene chromophore

The constitution of vacidin A, a representative of the aromatic heptaene macrolide antibiotics was established on the basis of 13C and 1H-1H double quantum filtered correlated spectroscopy, rotating frame nuclear Overhauser effect spectroscopy, J-resolved 1H as well as 1H-13C correlation NMR spectra. Geometry of the polyene chromophore was determined as 22E,24E,26E,28Z,30Z,32E,34E.

Comparative conformational analysis of cholesterol and ergosterol by molecular mechanics

A comparative conformational analysis of cholesterol and ergosterol has been carried out using molecular mechanics methods. These studies are aimed at giving a better understanding of the molecular nature of the interaction of these sterols with polyene macrolide antibiotics. Structures of cholesterol and ergosterol determined by X-ray methods have been used as initial geometries of these molecules for force field calculations. The calculation of steric energy has also been made for conformations which do not appear in the crystal. The latter conformers have different conformations of the side chain as well as different conformations of rings A and D. The rotational barriers around bonds C17-C20 and C20-C22 have also been calculated. The results obtained on differences and similarities in the conformations of cholesterol and ergosterol allow us to postulate a mechanism for differential interaction with the antibiotics. The relatively rigid side chain of ergosterol (stretched molecule) in comparison with the flexible side chain of cholesterol (bent molecule), allows better intermolecular contact of the first sterol molecule with a polyene macrolide and in consequence facilitates complex formation involving Van der Waal's forces.