Paclitaxel C-10 carbamates: potential candidates for the treatment of neurodegenerative tauopathies

A series of paclitaxel C-10 carbamates was synthesized and evaluated in a bi-directional permeability assay in comparison with paclitaxel and the blood-brain barrier-permeable C-10 ester derivative, TX-67. A number of the carbamates were found not to be substrates for Pgp. Moreover, when tested for Pgp-inhibitory potential, representative compounds proved to be devoid of Pgp interactions. Side-by-side comparison between TX-67 and the corresponding C-10 carbamate, CNDR-3, revealed a significantly longer half-life for CNDR-3 in both mouse and human plasma, suggesting that this class of derivatives is appropriate for further in vivo evaluation.     

Determination of isokinetic ratios necessary for equimolar incorporation of carboxylic acids in the solid-phase synthesis of mixture-based combinatorial libraries

The methods used to study the relative reaction rates of 45 different aliphatic and aromatic carboxylic acids when coupled to resin-bound amino acid amides is described. Competition experiments involving the coupling of incoming carboxylic acids to resin-bound amino acid amides were performed. The relative composition of each N-acylated amino acid amide in the resulting mixtures was compared to controls prepared by physically mixing equal aliquots of individual compounds in order to study the relative reaction rates of the incoming carboxylic acids. The ratios of the incoming carboxylic acids were then iteratively adjusted to yield as close to equimolar products as possible. As expected, the steric and electronic nature of the incoming carboxylic acids was found to influence their relative reaction rates. The steric hindrance of the resin-bound amino acid appears to have a proportional effect on the reaction rates of the incoming carboxylic acids. N-acylated amino acid amides in the final mixtures, prepared using the final isokinetic ratios, were found to be approximately equimolar.     

Synthesis and antifungal activity of substituted salicylaldehyde hydrazones,hydrazides and sulfohydrazides

Efficient synthetic procedures for the preparation of acid hydrazines and hydrazides were developed by converting the corresponding carboxylic acid into the methyl ester catalyzed by Amberlyst-15, followed by a reaction with hydrazine monohydrate. Sulfohydrazides were prepared from the corresponding sulfonyl chlorides and hydrazine monohydrate. Both of these group of compounds were condensed with substituted salicylaldehydes using gradient concentration methods that generated a large library of hydrazone, hydrazide and sulfohydrazide analogs. Antifungal activity of the prepared analogs showed that salicylaldehyde hydrazones and hydrazides are potent inhibitors of fungal growth with little to no mammalian cell toxicity, making these analogs promising new targets for future therapeutic development.     

High dopamine transporter selectivity can be displayed by remarkably simple non-nitrogen containing inhibitors

A series of 2-(3,4-dichlorophenyl)-cyclopent-1-enyl carboxylic acid esters and amides were prepared and tested for binding to the DAT, SERT, and NET. The achiral compounds were easily attained and found to inhibit DAT binding with K(i)-values ranging from 0.095 to 0.00003 mM. Among the compounds tested 2-(3,4-dichlorophenyl)-cyclopent-1-enyl carboxylic acid 2-methylphenyl ester was found to be highly selective with SERT/DAT>7000; NET/DAT>1700, K(i)=60 nM.     

Antigens from synthetic and natural estrogens: formation by conjugation with protein through a thiopropionic acid link

Formation of estra-1,3,5(10)-trienes substituted in the 7-position by a 3-thiopropionic acid side chain occurs by light-catalyzed reaction of β-mercaptopropionic acid with 1,3,5(10),6-estratetraenes. The reaction yields a mixture of α and β-epimers, which can be distinguished by their nmr spectra in pyridine. Both estrone and estradiol analogs were prepared. Addition of acetylene to estrone derivatives led to mestranol and ethynylestradiol analogs. The carboxylic acids were coupled with bovine serum albumin (with an incorporation of 25–30 steroid residues per albumin molecule) to yield antigens for the synthetic and natural estrogens which caused formation of specific antibodies.     

Study of P-glycoprotein effect on the lipid monolayer properties by the Langmuir-Blodgett technique

Expression of the P-glycoprotein (Pgp) is proved to be one of the main reasons for the development of the multidrug resistance (MDR) phenotype by cancer cells. The effect of Pgp on the properties of lipid monolayers was studied using membrane fractions of sensitive and Pgp over-expressing multidrug resistance cancer cells containing 11, 24 or 32% of Pgp relative to the total content of membrane proteins. The effect of the Pgp membrane concentration on the properties of monolayers prepared from the membrane fractions was analyzed by the Langmuir-Blodgett method. The subphase composition was found to play a critical role in the stability of monolayers at any Pgp concentration. The optimal subphase comprised 10 mM tris-HCl buffer, pH 6.5, which made it possible to create very stable monolayer films with the pressure of collapse of about 30-40 mN/m. Monolayers prepared from membrane fractions of sensitive cells and cells containing the maximum (32%) amount of Pgp were found to be much more stable compared with fractions comprising 11 or 24% of Pgp. The analysis of monolayer compression dynamics revealed three distinct stages: (1) the self-organization of lipid molecules, which is characterized by an abrupt change of surface potential; (2) the compression of Pgp molecules at the constant potential of monolayers; and (3) the compression of lipid molecules, which is characterized by a quasilinear increase of both pressure and surface potential. It was shown that the specific surface areas of monolayers formed from sensitive and Pgp-enriched membranes containing 11 or 24% of Pgp are very similar, whereas the surface area of the monolayer formed from membranes containing 32% of Pgp is nearly 1.5-fold greater. This fact may reflect the effect of the threshold rearrangement of the structure of lipid molecules or cooperative modifications of lipid-Pgp interactions induced by the increase in the Pgp content from 24 to 32%. The effect of verapamil, a well-known Pgp modulator, on the properties of monolayers was studied. It was show that verapamil is able to induce changes of the surface of Pgp-containing monolayers, and these modifications are maximal at the Pgp:verapamil 1:1 molar ratio. The data present the first experimental evidence for the possible intervention of Pgp modulator into the processes of lipid-lipid or lipid-Pgp cooperative interactions within Pgp-enriched membranes.     

Biotransformation of aromatic and heterocyclic amides by amidase of whole cells of Rhodococcus sp. MTB5: Biocatalytic characterization and substrate specificity

In this study, an amidohydrolase activity of amidase in whole cells of Rhodococcus sp. MTB5 has been used for the biotransformation of aromatic, monoheterocyclic and diheterocyclic amides to corresponding carboxylic acids. Benzoic acid, nicotinic acid and pyrazinoic acid are carboxylic acids which have wide industrial applications. The amidase of this strain is found to be inducible in nature. The biocatalytic conditions for amidase present in the whole cells of MTB5 were optimized against benzamide. The enzyme exhibited optimum activity in 50?mM potassium phosphate buffer pH 7.0. The optimum temperature and substrate concentrations for this enzyme were 50?°C and 50?mM, respectively. The enzyme was quite stable for more than 6?h at 30?°C. It showed substrate specificity against different amides, including aliphatic, aromatic and heterocyclic amides. Under optimized reaction conditions, the amidase is capable of converting 50?mM each of benzamide, nicotinamide and pyrazinamide to corresponding acids within 100, 160 and 120?min, respectively, using 5?mg dry cell mass (DCM) per mL of reaction mixture. The respective percent conversion of these amides was 95.02%, 98.00% and 98.44% achieved by whole cells. The amidase in whole cells can withstand as high as 383?mM concentration of product in a reaction mixture and above which it undergoes product feedback inhibition. The results of this study suggest that Rhodococcus sp. MTB5 amidase has the potential for large-scale production of carboxylic acids of industrial value.     

Bacillus cereus phospholipase C: carboxylic acid ester specificity and stereoselectivity

Thiophosphate analogs of phosphatidylcholine have been synthesized with varying structural complexity. These analogs have been used in a continuous spectrophotometric assay for phospholipase C (Bacillus cereus) to estimate the minimal structural requirements associated with the non-polar portion of the substrate phospholipid. The analogs were of three types containing zero, one or two carboxylic acid ester functionalities. The analogs with one or two ester groups acted as substrates for phospholipase C, while those without an ester functionality were not hydrolyzed. The rac-phosphatidylcholine analog with two ester functionalities gave biphasic time-course results, and was subsequently resolved into enantiomers by selective hydrolysis with a sterospecific phospholipase A2 (Crotalus atrox). The enantiomer with R absolute configuration was rapidly hydrolyzed by the phospholipase C while the enantiomer with the S configuration was slowly hydrolyzed after a long induction period. The results suggest that the B. cereus phospholipase C is specific for an ester functionality and is stereoselective for the R absolute configuration at glycerol C-2.     

Interaction of French-pressed liposomes with isolated bovine adrenal chromaffin cells. Characterization of the cell-liposome interactions

Small unilamellar liposomes with an average external diameter of approximately 550 A were prepared by high pressure extrusion in a French press. Liposomes, composed of phosphatidylcholine, phosphatidylserine, and cholesterol at a molar ratio of 7:1:2, were incubated with suspensions of bovine adrenal chromaffin cells. The cell-liposome interactions were characterized using fluorescence and radiotracer techniques. Transfer of the liposomal contents into the cytoplasm was visualized by fluorescence microscopy, using fluorescence-labeled macromolecules, and further documented by flow cytometry with liposome-entrapped 5,6-carboxy-fluorescein. The dose dependence, time course, and temperature dependence of the cell-liposome association, as determined by radioactive labeling both the liposomal membranes and their contents, indicate saturable interaction of the cells with intact liposomes (KappM approximately 5 X 10(-7) M lipid/10(6) cells at 37 degrees C). Using nonexchangeable fluorescent phospholipid analogs, the cell-liposome interactions were characterized by fluorescence resonance energy transfer and by fluorescence recovery after photobleaching. From these latter experiments we conclude that after 1-h incubation of 10(6) cells with 1 microM lipid at 37 degrees C, 30% of the cell-associated liposomes will have fused with the plasma membranes, resulting in the delivery of the contents of approximately 1.25 X 10(5) liposomes into each cell. Thus, liposomal delivery is an effective means to gain access to the cytoplasm and can be exploited to modulate physiological responses from within intact chromaffin cells.     

Evaluation of a diverse set of potential P1 carboxylic acid bioisosteres in hepatitis C virus NS3 protease inhibitors

There is an urgent need for more efficient therapies for people infected with hepatitis C virus (HCV). HCV NS3 protease inhibitors have shown proof-of-concept in clinical trials, which make the virally encoded NS3 protease an attractive drug target. Product-based NS3 protease inhibitors comprising a P1 C-terminal carboxylic acid have shown to be effective and we were interested in finding alternatives to this crucial carboxylic acid group. Thus, a series of diverse P1 functional groups with different acidity and with possibilities to form a similar, or an even more powerful, hydrogen bond network as compared to the carboxylic acid were synthesized and incorporated into potential inhibitors of the NS3 protease. Biochemical evaluation of the inhibitors was performed in both enzyme and cell-based assays. Several non-acidic C-terminal groups, such as amides and hydrazides, were evaluated but failed to produce inhibitors more potent than the corresponding carboxylic acid inhibitor. The tetrazole moiety, although of similar acidity to a carboxylic acid, provided an inhibitor with mediocre potencies in both assays. However, the acyl cyanamide and the acyl sulfinamide groups rendered compounds with low nanomolar inhibitory potencies and were more potent than the corresponding carboxylic acid inhibitor in the enzymatic assay. Additionally, results from a pH-study suggest that the P(1) C-terminal of the inhibitors comprising a carboxylic acid, an acyl sulfonamide or an acyl cyanamide group binds in a similar mode in the active site of the NS3 protease.     

Direct amidation of poly(gamma-glutamic acid) with benzylamine in dimethyl sulfoxide

Partially benzylamidated, amphipathic poly(gamma-glutamic acid) (BzPGA) was synthesized from poly(gamma-glutamic acid) (PGA) and benzylamine by direct amidation in dimethyl sulfoxide (DMSO). Benzylamine and PGA were heated in DMSO for 1 to 26 h at temperatures between 110 and 130 degrees C, producing derivatives of various degrees of benzylamidation as a function of the reaction time and temperature. Neither any carboxyl-activating agent nor catalyst is needed for the reaction to proceed. After purification by dialysis, the product was identified by 1H and 13C 1D and 2D NMR in DMSO-d(6). BzPGA prepared by the new direct amidation method was identical to that obtained with a conventional carbodiimide-mediated reaction in water. The one-pot amidation procedure described in the present article can probably be applied to the synthesis of amides from other amines and carboxylic acids.     

Synthesis of γ-aminobutyric acid analogs based on carbohydrate scaffolds

γ-Aminobutyric acid analogs based on sugar scaffolds were prepared in six to nine steps starting from d-glucal and d-galactal. The key step in the synthesis is the Vilsmeier-Haack reaction that affords the corresponding 2-C-formyl glycal on treatment with DMF and POCl₃. Oxidation of the aldehyde and reduction of the 4-azido group provided the corresponding GABA analog. Acylamide and tetrazole analogs were also prepared as the bioisosteres of the carboxylic acid.     

New metabolically stable fatty acid amide ligands of cannabinoid receptors: Synthesis and receptor affinity studies

We investigated the structure-activity relationships for the interactions of fatty acid amide analogs of the endocannabinoid anandamide with human recombinant cannabinoid receptors. Thirty-five novel fatty acid amides were synthesized using five different types of acyl chains and 11 different aromatic amine 'heads.' Although none of the new compounds was a more potent ligand than anandamide, we identified three amine groups capable of improving the metabolic stability of arachidonoylamides and their CB(1)/CB(2) selectivity ratio to over 20-fold, and several aromatic amines capable of improving the affinity of short chain or monosaturated fatty acids for cannabinoid CB(1) receptors. For the first time a tertiary amide of arachidonic acid was found to possess moderate affinity (K(i)=300 nM) for cannabinoid CB(1), but not CB(2), receptors.     

Synthesis and biological effects of some kynurenic acid analogs

The overactivation of excitatory amino acid receptors plays a key role in the pathomechanism of several neurodegenerative disorders and in ischemic and post-ischemic events. Kynurenic acid (KYNA) is an endogenous product of the tryptophan metabolism and, as a broad-spectrum antagonist of excitatory amino acid receptors, may serve as a protective agent in neurological disorders. The use of KYNA is excluded, however, because it hardly crosses the blood–brain barrier. Accordingly, new KYNA analogs which can readily cross this barrier and exert their complex anti-excitatory activity are generally needed. During the past 6 years, we have developed several KYNA derivatives, among others KYNA amides. These new analogs included one, N-(2-N,N-dimethylaminoethyl)-4-oxo-1H-quinoline-2-carboxamide hydrochloride (KYNA-1), that has proved to be neuroprotective in several models.This paper reports on the synthesis of 10 new KYNA amides (KYNA-1–KYNA-10) and on the effectiveness of these molecules as inhibitors of excitatory synaptic transmission in the CA1 region of the hippocampus. The molecular structure and functional effects of KYNA-1 are compared with those of other KYNA amides. Behavioral studies with these KYNA amides demonstrated that they do not exert significant nonspecific general side-effects. KYNA-1 may therefore be considered a promising candidate for clinical studies.     

Noncatalytic reaction of isonitriles and carboxylic acids en route to amide-type linkages

This protocol describes the preparation of an N-methyl-asparagine-linked glycosyl amino acid, on the basis of a reaction between carboxylic acids and isonitriles. Under microwave/thermolysis, carboxylic acids can couple with isonitriles without an external catalyst to form N-formyl-amides, which may be further advanced to the corresponding amides, N-methyl amide and N-methyloyl amide. The example reaction of beta-galactopyranosyl isonitrile (7) with a protected aspartic acid under microwave condition in 30 min stereoselectively leads to a beta-galactopyranosyl-N-formyl-asparagine (9). Further chemical transformations readily convert 9 into beta-galactopyranosyl-N-methyl-asparagine (11).     

Further optimization of sulfonamide analogs as EP1 receptor antagonists: synthesis and evaluation of bioisosteres for the carboxylic acid group

4-{[2-[(2-Furylsulfonyl)(isobutyl)amino]-5-(trifluoromethyl)phenoxy]methyl}benzoic acid analogs 2a and b and a series of the acid analogs, in which the carboxylic acid residue of 2b was replaced with various kinds of carboxylic acid bioisosteres, were synthesized and evaluated as EP1 receptor antagonists. Compound 2b and its monocyclic acid analogs, in which the carboxylic acid residue of 2b was replaced with monocyclic acid bioisosteres, were found to show potent EP1 receptor antagonist activity. Optimization of the linker Y between the phenyl moiety and the carboxylic acid residue of 2b was also carried out (Table 5). Compounds 2b and 16 and 17 possessing conformationally restricted linker Y were found to show the most optimized potency among the tested compounds. Cytochrome P450 inhibition of optimized compounds was also investigated. Details of the structure-activity relationship study are presented.     

An efficient conversion of carboxylic acids to one-carbon degraded aldehydes via 2-hydroperoxy acids

After the formation of dianions of a carboxylic acid with lithium diisopropylamide, oxygen was bubbled into the solution to produce 2-hydroperoxy acid. Then the reaction mixture was acidified with a 2 N HCl solution and subsequently elevated to 50 degrees C to afford the aldehyde with the loss of one carbon atom. Even saturated (C(10)-C(20)) and unsaturated (C(18:1)) carboxylic acids were converted into the odd aldehydes (C(9)-C(19), C(17:1)) in high yields. This conversion was found to be an efficient method for the preparation of carboxylic acids (Cn) to one-carbon degraded aldehydes (Cn-1) via 2-hydroperoxy acids.     

微生物共同作用下的铁皮石斛组培苗生长效应研究

植物体和植物根际均是复杂的微生态系统,其内栖息着关系复杂的共生微生物,共同影响植物的生长发育.为探讨混合接种真菌与细菌对兰科植物生长的影响,筛选出真菌与细菌的优势促生组合,本研究选取经分离、筛选获得的4株促生内生真菌(铁皮石斛内生真菌C22、C35,美花石斛内生真菌L12、L28)和3株促生内生细菌(铁皮石斛菌内生细菌TX-7、TX-16、TX-19),以"真菌+细菌"的方式混合接种于铁皮石斛无菌组培苗中,共培养120 d.结果获得了3组优势组合:C22+TX-19、L28+TX-16和L28+TX-19,它们对铁皮石斛组培苗的生长均表现出正效应,其中C22+TX-19和L28+TX-19对促进组培苗生物量的增长具有协同效应,L28+TX-19对提高组培苗的根分枝率具有协同效应,3个组合对增加组培苗的分蘖数和根尖数均表现为累加效应.研究结果表明,内生真菌与内生细菌的共同作用可显著促进铁皮石斛的生长,混合接种有可能更大地发挥微生物的效能.     

Design and synthesis of a library of tertiary amides: evaluation as mimetics of the melanocortins' active core

Two hundred and ten tertiary amides were prepared on solid phase. Diamines were coupled to activated carboxylated Wang polymer, and the polymeric substituted benzyloxycarbonyl protected diamines obtained were reacted with aldehydes or ketones in trimethyl orthoformate giving resin attached Schiff bases. Coupled resins were then reduced to secondary amines by sodium cyanoborohydride in 4% acetic acid/trimethyl orthoformate, followed by acylation with the carboxylic acid in the presence of PyBroP and diisopropylethylamine. Cleavage of tertiary amides from the resin was made by trifluoroacetic acid in the presence of scavengers (mainly 1,2-ethanedithiol). When indole derivatives were prepared, parallel alkylation with the linker fragment occurred, giving derivatives of 2-(4-hydroxybenzyl)-indole as side products. Solution synthesis or mixed liquid/solid phase preparation of title substances proved to be advantageous in cases when the above method did not give acceptable results. According to this approach an efficient formation of Schiff bases was achieved in the presence of TiCl(4). Substances were isolated by reversed phase chromatography; in some cases isomers were additionally separated by chiral chromatography on Chirobiotic T. When tested on human recombinant melanocortin receptors all the tertiary amides showed some binding affinities; for the highest affinity compounds the K(i)s reached 400 nM on MC(1), 2 microM on MC(3) and 1 microM on MC(4) and MC(5) receptors. cAMP assays of some of the title compounds showed that the tertiary amides are melanocortin receptor antagonists on the four MC receptor subtypes.     

Protein heat denaturation and study of membrane lipid-protein interactions by spin label ESR.

Spinach chloroplast membranes labelled with stearic acid-spin probe-bearing nitroxyl (label) moiety at 5th, 9th, 12th, 13th, 14th or 16th carbon locations with respect to the carboxylic group of stearic acid were studied (in the dark) by electron spin resonance (ESR) spectroscopy. Spectra were recorded at sample temperatures of 5, 30 and 67 degrees C. After heat denaturation of the membrane proteins for 5 min at 67 degrees C, the spectra were re-recorded at 30 and 5 degrees C for comparison. The results unequivocally show that membrane lipid fatty-acyl chains become substantially more rigid after protein heat-denaturation. The data throw light on the degree of lipid-protein interactions at various microlocations along the length of fatty-acyl chains of the membrane lipid matrix.