Amide and ester derivatives of N3-(4-methoxyfumaroyl)-(S)-2,3-diaminopropanoic acid: the selective inhibitor of glucosamine-6-phosphate synthase

Several amide and ester derivatives of a glutamine analogue, N3-(4-methoxyfumaroyl)-(S)-2,3-diaminopropanoic acid (FMDP) (1-8), were synthesized and evaluated for the inhibitory activity in regard to glucosamine-6-phosphate synthase from Candida albicans. The syntheses were accomplished by the reaction of N2-tert-butoxycarbonyl-N3-(4-methoxyfumaroyl)-(S)-2,3-diaminopropanoic acid (BocFMDP) with the corresponding amines to give the FMDP amides (1-4) or with alkyl halides to give corresponding esters of FMDP (5-8). Among the synthesized compounds, the acetoxymethyl ester of FMDP was the most active inhibitor of the enzyme. Its IC50 value compared to that of FMDP (4 microM) was equal to 11.5 microM. The methyl and allyl esters and the N-hexyl-N-methyl-amide of FMDP exhibited a moderate enzyme inhibitory activity.     

Synthesis and evaluation of novel 2-pyridone derivatives as inhibitors of phosphodiesterase3 (PDE3): A target for heart failure and platelet aggregation

Twenty-six 2-pyridone derivatives (8a-8z), which are structurally analogous to amrinone and milrinone two important cardiotonic drugs, are synthesized and characterized. The synthesis of 2-pyridone derivatives involves addition, followed by cyclization between Baylis-Hillman acetates (7a-7k) and enamino esters or nitriles (3a-3e). Thus synthesized pyridones were subjected to PDE3 inhibitory activity, 14 pyridones were found to be hits out of 26 pyridones synthesized and out of 14 hits, there are 5 pyridones found to be lead compounds having excellent PDE3 inhibitory activity. Further we have carried out computational analysis to understand protein/enzyme and 2-pyridone derivative interactions to identify amino acid residues involved in the vicinity of binding and compared with milrinone drug.     

Hydrolysis of phosphonate esters catalyzed by 5'-nucleotide phosphodiesterase.

4-Nitrophenyl and 2-napthyl monoesters of phenylphosphonic acid have been synthesized, and an enzyme catalyzing their hydrolysis was resolved from alkaline phosphatase of a commerical calf intestinal alkaline phosphatase preparation by extensive ion-exchange chromatography, chromatography on L-phenylalanyl-Sepharose with a decreasing gradient of (NH4) 2SO4, and gel filtration. Detergent-solubilized enzyme from fresh bovine intestine was purified after (NH4)2SO4 fractionation by the same technique. The purified enzyme is homogeneous by polyacrylamide gel electrophoresis and sedimentation equilibrium centrifugation. It has a molecular weight of 108,000, contains approximately 21% carbohydrate, and has an amino acid composition considerably different from that reported from alkaline phosphatase from the same tissue. The homogeneous intestinal enzyme, an efficient catalyst of phosphonate ester hydoolysis but not of phosphate monoester hydrolysis, was identified as a 5'-nucleotide phosphodiesterase by its ability to hydrolyze 4-nitrophenyl esters of 5'-TMP but not of 3'-TMP. Also consistent with this identification was the ability of the enzyme to hydrolyze 5'-ATP to 5'-AMP and PPi, NAD+ to 5'-AMP and NMN, TpT to 5'-TMP and thymidine, pApApApA to 5'-AMP, and only the single-stranded portion of tRNA from the 3'-OH end. Snake venom 5'-nucleotide phosphodiesterase also hydrolyzes phosphonate esters, but 3'-nucleotide phosphodiesterase of spleen and cyclic 3',5'-AMP phosphodiesterase do not. Thus, types of phosphodiesterases can be conveniently distinguished by their ability to hydrolyze phosphonate esters. As substrates for 5'-nucleotide phosphodiesterases, phosphonate esters are preferable to the more conventional esters of nucleotides and bis(4-nitrophenyl) phosphate because of their superior stability and ease of synthesis. Furthermore, the rate of hydrolysis of phosphonate esters under saturating conditions is greater than that of the conventional substrates. At substrate concentrations of 1 mM the rates of hydrolysis of phosphonate esters and of nucleotide esters are comparable and both superior to that of bis(4-nitrophenyl) phosphate.     

Synthesis and reactivity of guanosine 3′,5′-phosphoric acid alkyl esters

Guanosine 3′,5′-phosphoric acid alkyl esters were synthesized by reaction of the free acid of guanosine 3′,5′-phosphate (cGMP) with the appropriate diazoalkane. The resulting pair of diastereoisomers was separated chromatographically, and the conformations were assigned on the basis of ³¹P-nmr. Hydrolysis of the compounds in water was measured, and their half-lives were determined. The ability of the compounds to act as substrates for phosphodiesterase from beef heart was tested, and their inhibition of this enzyme was measured.     

Structure-activity study of phosphoramido acid esters as acetylcholinesterase inhibitors

Phosphoramido acid esters (CH(3))(2)NP(O)X(p-OC(6)H(4)-CH(3)) (containing P-Cl (1), P-O (2), P-F (3), P-CN (5), and P-N (4,6) bonds, X for 2, 4 and 6 is OCH(3), (C(2)H(5))(2)N and morpholin) have been synthesized to investigate the structure-activity study of AChE enzyme inhibition, through the parameters logP, delta(31)P and IC(50). After their characterization by (31)P, (31)P{(1)H}, (13)C, (1)H NMR, IR and mass spectroscopy, the parameters logP and delta(31)P ((31)P chemical shift in NMR) were used to evaluated the lipophilicity and electronical properties. The ability of compounds to inhibit human AChE was predicted by PASS software (version 1.193), and experimentally evaluated by a modified Ellman's assay.     

Alkyl esters of hydroxycinnamic acids with improved antioxidant activity and lipophilicity protect PC12 cells against oxidative stress

Hydroxycinnamic acids (HCAs) are phenolic compounds present in dietary plants, which possess considerable antioxidant activity. In order to increase the lipophilicity of HCAs, with the aim of improving their cellular absorption and expansion of their use in lipophilic media, methyl, ethyl, propyl and butyl esters of caffeic acid and ferulic acid have been synthesized. All caffeate esters had a slightly lower DPPH IC(50) (13.5-14.5 μM) and higher ferric reducing antioxidant power (FRAP) values (1490-1588 mM quercetin/mole [mMQ/mole]) compared to caffeic acid (16.6 μM and 1398 mMQ/mole, respectively) in antioxidant assays. In contrast, ferulate esters were less active in DPPH (56.3-74.7 μM) and FRAP assays (193-262 mMQ/mole) compared to ferulic acid (44.6 μM and 324 mMQ/mole, respectively). Redox properties of HCAs were in line with their antioxidant capacities, so that compounds with higher antioxidant activities had lower oxidation potentials. Measurement of partition coefficients disclosed the higher lipophilicity of the esters compared to parent compounds. All esters of caffeic acid significantly inhibited hydrogen peroxide-induced neuronal PC12 cell death assessed by MTT assay at 5 and 25 μM. However, caffeic acid, ferulic acid and ferulate esters were not able to protect the cells. In conclusion, these findings suggest that alkyl esterification of some HCAs augments their antioxidant properties as well as their lipophilicity and as a consequence, improves their cell protective activity against oxidative stress. These compounds could have useful applications in conditions where oxidative stress plays a pathogenic role.     

Synthesis and conformational studies of 2-beta-chloro, 1-alpha-fluoro, and 2-beta-fluoro derivatives of 2-deoxy-N-acetyl-neuraminic acid

5-Acetamido-4,7,8,9-tetra-O-acetyl-2,3,5-trideoxy-2-fluoro-D-glycero-alp ha- and -beta-D- galacto -2- nonulosonic acid methyl esters and the beta-chloro analog were synthesized from N-acetylneuraminic acid. Their 1H- and 13C-n.m.r.spectra were completely assigned by using single-frequency decoupling, off-resonance decoupling, and spin-simulation programs. Bond angles estimated from the 1H coupling-constants indicate that all of the compounds adopt the 2C5 (L) conformation with minor conformational differences in the C3 side chain. 5-Acetamido-2,3,5,-tri-deoxy-2-fluoro-D-glycero-alpha- and -beta-D- galacto -2- nonulosonic acid and their methyl esters were also prepared.     

Synthesis of novel vasodilatory active nicotinate esters with amino acid function

A variety of N-[(ethyl-4,6-diaryl-3-pyridinecarboxylate)-2-yl]amino acid esters 6a–h were synthesized through the reaction of 2-bromonicotinates 4 with a number of primary amino acid ester hydrochlorides 5 in refluxing tetrahydrofuran in the presence of triethylamine as dehydrohalogenating agent. Similarly, reaction of 4 with N-glycylglycine ethyl ester hydrochloride 7 ‘as a representative example of dipeptide derivative’ afforded smoothly the corresponding N-[(ethyl-4,6-diaryl-3-pyridinecarboxylate)-2-yl]-N′-glycylglycine ethyl ester analogues 8. However, reaction of 4 with 5 in refluxing pyridine yielded the unexpected 2-aminonicotinate esters 9. Vasodilation activity screening for the synthesized nicotinate esters was investigated in vitro on the contractile response of vascular thoracic aorta smooth muscle from Wistar rats, where all the tested compounds exhibit considerable vasodilatory properties. In addition, few prepared compounds especially, 6b, 6h and 9b reveal remarkable vasodilation potency (IC₅₀).     

A comparison of the fatty acid esters of estradiol and corticosterone synthesized by tissues of the rat

The biosynthesis of the fatty acid esters of the corticoid (corticosterone) and estrogen (estradiol) was compared in parallel incubations of corticosterone and estradiol with several tissues of the rat. The fatty acid composition of the esters of the two steroids was characterized in mammary and uterine tissue. In both of these tissues, the esters of estradiol were extremely heterogeneous. To the contrary, in the same tissues only one predominant ester of corticosterone, corticosterone-21-oleate, was formed. It comprised 70-80% of the total. The oleate ester of estradiol accounted for only 20% of the esters of this estrogen. In addition, fatty acid esters of an A-ring reduced metabolite of corticosterone, 5 beta-dihydrocorticosterone, was also identified. Its fatty acid composition is identical to that of corticosterone. In other experiments the fatty acid esters of both steroids were isolated from several tissues and quantified. When the amount of steroidal ester formed was compared, there was over a 100-fold difference among the various tissues in the ratio of estradiol to corticosterone ester synthesized. Thus, the rate of synthesis of the fatty acid esters of each class of steroid varies dramatically from tissue to tissue, and their fatty acid composition differs markedly as well. If the same enzyme synthesized both the estrogen and corticoid esters, then it would be expected that the relative amount of both esters synthesized in various tissues should be constant and likewise that their composition should be the same. Since neither occurred, these results suggest that the enzyme which produces the C-17 fatty acid esters of the estrogens may be different from the one which synthesizes the C-21 esters of the corticoids. The existence of separate enzyme systems for the synthesis of the fatty acid esters of these steroid hormones opens the possibility of specific physiological controls of each of these unusual steroidal metabolites.     

Purification and characterization of two oxidoreductases involved in the enantioselective reduction of 3-oxo, 4-oxo and 5-oxo esters in baker's yeast

Two NADPH-dependent oxidoreductases catalyzing the enantioselective reduction of 3-oxo esters to (S)- and (R)-3-hydroxy acid esters, [hereafter called (S)- and (R)-enzymes] have been purified 121- and 332-fold, respectively, from cell extracts of Saccharomyces cerevisiae by means of streptomycin sulfate treatment, Sephadex G-25 filtration, DEAE-Sepharose CL-6B chromatography, Sephadex G-150 filtration, Sepharose 6B filtration and hydroxyapatite chromatography. The relative molecular mass Mr, of the (S)-enzyme was estimated to be 48,000-50,000 on Sephadex G-150 column chromatography and 48,000 on sodium dodecyl sulfate/polyacrylamide gel electrophoresis. The enzyme was most active at pH 6.9 and reduced 3-oxo esters, 4-oxo and 5-oxo acids and esters enantioselectively to (S)- hydroxy compounds in the presence of NADPH. The Km values for ethyl 3-oxobutyrate, ethyl 3-oxohexanoate, 4-oxopentanoic and 5-oxohexanoic acid were determined as 0.9 mM, 5.3 mM, 17.1 mM and 13.1 mM, respectively. The Mr of the (R)-enzyme, estimated by means of column chromatography on Sepharose 6B, was 800,000. Under dissociating conditions of SDS/polyacrylamide gel electrophoresis the enzyme resolved into subunits of Mr 200,000 and 210,000, respectively. The enzyme is optimally active at pH 6.1, catalyzing specifically the reduction of 3-oxo esters to (R)-hydroxy esters, using NADPH for coenzyme. Km values for ethyl 3-oxobutyrate and ethyl 3-oxohexanoate were determined as 17.0 mM and 2.0 mM, respectively. Investigations with purified fatty acid synthase of baker's yeast revealed that the (R)-enzyme was identical with a subunit of this multifunctional complex; intact fatty acid synthase (Mr 2.4 X 10(6)) showed no activity in catalyzing the reduction of 3-oxo esters.     

N-(5-Methyl-1,3-Thiazol-2-yl)-2-{[5-((Un)Substituted- Phenyl)1,3,4-Oxadiazol-2-yl]Sulfanyl}acetamides. Unique Biheterocycles as Promising Therapeutic Agents

An electrophile, 2-bromo-N-(5-methyl-1,3-thiazol-2-yl)acetamide, was synthesized by the reaction of 5-methyl-1,3-thiazol-2-amine and bromoacetyl bromide in an aqueous medium. In a parallel scheme, a series of (un)substituted benzoic acids was converted sequentially into respective esters, acid hydrazides, and then into 1,3,4-oxadiazole heterocyclic cores. The electrophile was coupled with the aforementioned 1,3,4-oxadiazoles to obtain the targeted bi-heterocyles. Structural analysis of the synthesized compounds was performed by IR, EI-MS, ¹H NMR, and ¹³C NMR. The enzyme inhibition study of these molecules was carried out against four enzymes, namely, acetylcholinesterase, butyrylcholinesterase, α-glucosidase, and urease. The interactions of these compounds with respective enzymes were recognized by their in silico study. Moreover, their cytotoxicity was also determined to find out their utility as possible therapeutic agents.

     

Design and synthesis of 3-(4,5,6,7-tetrahydro-3H-imidazo[4,5-c]pyridin-2-yl)-1H-quinolin-2-ones as VEGFR-2 kinase inhibitors

A series of 3-(4,5,6,7-tetrahydro-3H-imidazo[4,5-c]pyridin-2-yl)-1H-quinolin-2-ones have been identified as a new class of VEGFR-2 kinase inhibitors. A variety of (4,5,6,7-tetrahydro-imidazo[5,4-c]pyridin-2-yl)-acetic acid ethyl esters were synthesized, and their VEGFR-2 inhibitory activity was evaluated. Described herein are the preparation of the series and the effects of the compounds on VEGFR-2 kinase activity.     

Synthesis,structure elucidation,and chemiluminescent activity of new 9-substituted 10-(ω-(succinimidyloxycarbonyl)alkyl)acridinium esters

Several new acridinium esters 2 – 9 having their central acridinium ring bearing a 9-(2,5-dimethylphenoxycarbonyl), 9-(2,6-bis(trifluoromethyl)phenoxycarbonyl) or 9-(2,6-dinitrophenoxycarbonyl) group, and a 10-methyl, 10-(3-(succinimidyloxycarbonyl)propyl), 10-(5-(succinimidyloxycarbonyl)pentyl), or 10-(10-(succinimidyloxycarbonyl)decyl) group, have been synthesized and their chemiluminescent properties have been tested. The 2,5-dimethylphenyl acridinium esters emit light slowly (glow) when treated with alkaline hydrogen peroxide, while the 2,6-dinitrophenyl and 2,6-bis(trifluoromethyl)phenyl esters emit light rapidly (flash). The substituent at the 10 position affects the hydrolytic stabilities of the compounds.     

Research in the field of imidazo[1,2-<Emphasis Type="Italic">a</Emphasis>]benzimidazole derivatives. XXX. Synthesis and properties of (imidazo[1,2-<Emphasis Type="Italic">a</Emphasis>]benzimidazolyl-2)acetic acids

Ethyl esters of (9-subtituted-imidazo[1,2-a]benzimidazolyl-2)acetic acids have been synthesized. The chemical properties of these esters have been studied: hydrolysis, decarboxylation, hydrazinolysis, and hydrazone formation. Some of these compounds demonstrate biological activity (fungicidal, antimicrobial, antiarrhythmic) and effects on brain rhythmogenesis.     

Determination of abscisic acid in Eucalyptus haemastoma leaves using gas chromatography/mass spectrometry and deuterated internal standards

Abscisic acid and 2-trans-abscisic acid each with three deuterium atoms in the C-3 methyl group, have been synthesized chemically and used as internal standards in selected ion monitoring experiments to establish the endogeneous concentrations of these compounds and their conjugates in turgid and wilted Eucalyptus haemastoma leaves. The analytical procedure used GC/CIMS(methane) to detect the methyl esters of abscisic acid, 2-trans-abscisic acid and their deuterated internal standards. A three-fold increase in the concentration of abscisic acid occurred on wilting and the amounts of 2-trans-abscisic acid and conjugates of both compounds were determined.     

Synthesis and Use of New Semispecific Substrates for Trypsin-Catalyzed Peptide Bond Formation

Two series of semispecific acyl donors, hydroxyalkyl esters of Z-Ala-OH and TV-modified carboxamidomethyl (Cam) esters of Z-Xaa-OH (Xaa = Ala, Leu, Phe) were synthesized as substrates for trypsin-catalyzed peptide synthesis. It follows from the specificity constants of these compounds, that the carboxamidomethyl derivatives are well accepted by trypsin due to favourable S₂′ – P₂′ interactions. These new substrates can be successfully used for the trypsin-mediated formation of dipeptide amides. The synthesis outcome depends on the amino acid in the P₁ position, the ability of the leaving group to provide efficient interactions with the enzyme subsite and the hydrophobicity of the nucleophilic amino acid amide. The modified Cam esters give better peptide yields in comparison to the unmodified ones.     

Synthesis and antimycobacterial activity of some alkyl [5-(nitroaryl)-1,3,4-thiadiazol-2-ylthio]propionates

Two series of 2- and 3-[5-(nitroaryl)-1,3,4-thiadiazol-2-ylthio, sulfinyl and sulfonyl] propionic acid alkyl esters were synthesized and screened for antituberculosis activity against Mycobacterium tuberculosis H37Rv using the BACTEC 460 radiometric system. The MIC values for the compounds showing more than 90% inhibition were determined. The result of comparison between two groups of data exhibited that among the synthesized derivatives, the compound propyl 3-[5-(5-nitrothiophen-2-yl)-1,3,4-thiadiazol-2-ylthio]propionate was the most active one (MIC=1.56 microgml(-1)).     

Investigating the activity of 2-substituted alkyl-6-(2,5-dioxopyrrolidin-1-yl)hexanoates as skin penetration enhancers

Skin penetration enhancers are used in the formulation of transdermal delivery systems for drugs that are otherwise not sufficiently skin-permeable. We generated two series of esters by multi-step synthesis with substituted 6-aminohexanoic acid as potential transdermal penetration enhancers by multi-step synthesis. The synthesis of all newly prepared compounds is presented here. Structure confirmation of all generated compounds was accomplished by (1)H NMR, (13)C NMR, IR and MS spectroscopy. All the prepared compounds were analyzed using RP-HPLC and their lipophilicity (logk) was determined. The hydrophobicity (logP/ClogP) of the studied compounds was also calculated using two commercially available programs and 3D structures of the selected compounds were investigated by means of ab initio calculations of geometry and molecular dynamic simulations. All the synthesized esters were tested for their in vitro transdermal penetration-enhancing activity and showed higher enhancement ratios than oleic acid. The highest enhancement ratios were exhibited by compound 5f (C((2)) substituted with piperidine-2-one, C(11) ester chain) and 5a (C((2)) substituted with piperidine-2-one, C(6) ester chain). The series with a ω-lactam ring (piperidin-2-one; 5a-g), showed slightly higher activities than those with morpholine (6a-6g). All of the agents showed minimal anti-proliferative activity (IC(50) >6.25μM), indicating they would have low cytotoxicity when administered as chemical penetration enhancers. The relationships between the lipophilicity and the chemical structure of the studied compounds, as well as the correlation between their chemical structure and transdermal penetration-enhancing activity, are discussed.     

Synthesis and biological evaluation of 2-alkoxycarbonylallyl esters as potential anticancer agents

The reaction of carboxylic acids with Baylis-Hillman reaction derived α-bromomethyl acrylic esters readily provide 2-(alkoxycarbonyl)allyl esters in good to excellent yields. These functionalized allyl esters have been evaluated for their cell proliferation inhibition properties against breast cancer (MDA-MB-231 and 4T1) and pancreatic cancer (MIAPaCa-2) cell lines to explore their potential as anticancer agents. Several of the synthesized derivatives exhibit good potency against all three cancer cell lines. Our structure activity relationship (SAR) studies on 2-carboxycarbonyl allyl esters indicate that substituted aromatic carboxylic acids provide enhanced activity compared to substituted aliphatic carboxylic acid analogs. Di- and tri-allyl esters derived from di-and tri-carboxylic acids exhibit higher inhibition of cell proliferation than mono esters. Further SAR studies indicate that the double bond in the 2-(alkoxycarbonyl)allyl ester is required for its activity, and there is no increase in activity with increased chain length of the alkoxy group. Two lead candidate compounds have been identified from the cell proliferation inhibition studies and their preliminary mechanism of action as DNA damaging agents has been evaluated using epifluorescence and western blot analysis. One of the lead compounds has been further evaluated for its systemic toxicity in healthy CD-1 mice followed by anticancer efficacy in a triple negative breast cancer MDA-MB-231 xenograft model in NOD-SCID mice. These two in vivo studies indicate that the lead compound is well tolerated in healthy CD-1 mice and exhibits good tumor growth inhibition compared to breast cancer drug doxorubicin.     

Synthesis and pharmacological properties of novel hydrophilic 5-HT4 receptor antagonists

Serotonin (5-hydroxytryptamine, 5-HT) is an important signalling molecule in the human body. The 5-HT(4) serotonin receptor, coupled to the G protein G(s), plays important physiological and pathophysiological roles in the heart, urinary bladder, gastrointestinal tract and the adrenal gland. Both 5-HT(4) antagonists and agonists have been developed in the aim to treat diseases in these organs. 5-HT(4) agonists might have beneficial effects in the central nervous system (CNS) and therefore, 5-HT(4) antagonists might cause CNS side effects. In this study, we have developed new amphoteric 5-HT(4) antagonists. A series of cyclic indole amide derivatives possessing an oxazine ring and a piperidine alkane carboxylic acid side chain and the corresponding prodrug esters were synthesized and their binding to 5-HT(4) receptors and antagonist properties were evaluated. In addition, an indole ester without the oxazine ring and the corresponding indole amide derivatives were also tested. Octanol-water distribution (LogD(Oct7.4)) was tested for some of the synthesized ligands. The main structure-affinity characteristics of the 5-HT(4) compounds tested were that the prodrug esters show higher affinity than their corresponding free acids, indole esters show higher affinity than the corresponding amides and ligands containing the oxazine ring in the indole skeleton show higher affinity than indole derivatives not containing the ring. One representative prodrug ester and its corresponding free acid were tested for binding on a panel of receptors and showed preserved selectivity for the 5-HT(4) receptor. These new molecules may be useful to target peripheral 5-HT(4) receptors.