First total synthesis of (5Z,9Z)-(+/-)-2-methoxy-5,9-octadecadienoic acid, a marine derived methoxylated analog of taxoleic acid

The first total synthesis for the sponge derived (5Z,9Z)-(+/-)-2-methoxy-5,9-octadecadienoic acid, an analog of taxoleic acid, was accomplished in seven steps and in a 10% overall yield. It was again corroborated that the best strategy to prepare these cis,cis dimethylene interrupted double bonds is the double-alkyne bromide coupling reaction of 1,5-hexadiyne, which provides the advantage of achieving a 100% cis stereochemical purity for both double bonds after hydrogenation under Lindlar conditions. The alpha-methoxy functionality was best prepared via the Mukaiyama reaction of (4Z,8Z)-heptadecadienal with trimethylsilyl cyanide and triethylamine followed by acid hydrolysis. Selective methylation of the hydroxyl group of (5Z,9Z)-(+/-)-2-hydroxy-5,9-octadecadienoic acid was achieved with sodium hydride/methyl iodide when tetrahydrofuran was used as solvent. Complete spectral data is presented, for the first time, for this unusual marine alpha-methoxylated fatty acid.     

Self-association of adenosine 5'-monophosphate (5'-AMP) as a function of pH and in comparison with adenosine, 2'-AMP and 3'-AMP

The concentration dependence of the chemical shifts for protons H-2, H-8, and H-1' of adenosine (Ado), 2'-AMP, 3'-AMP and 5'-AMP was measured in D2O at 27 degrees C under several degrees of protonation. All results are consistent with the isodesmic model of indefinite noncooperative stacking. The association constants for Ado decrease with increasing protonation: Ado (K = 15 M-1) greater than D(Ado)+/Ado (6.0 M-1) greater than D(Ado)+ (0.9 M-1). In contrast, a maximum is observed with 5'-AMP: 5'-AMP2- (K = 2.1 M-1) less than D(5'-AMP)- (3.4 M-1) less than D2(5'-AMP) +/- /D(5'-AMP)- (5.6 M-1) greater than D2(5'-AMP) +/- (approximately 2 M-1) greater than D3(5'-AMP)+ (less than or equal to 1 M-1). Self-stacking is most pronounced here if 50% of the adenine residues are protonated at N-1; complete base protonation reduces the stacking tendency drastically. Comparing the self-association of 2'-, 3'- and 5'-AMP shows that there is no influence of the phosphate-group position in the 2-fold negatively charged species, i.e., K congruent to 2 M-1 for all three AMP2- species. More importantly, there is also no significant influence observed if the stacking tendency of the three D2(AMP) +/- /D(AMP)-1:1 mixtures is compared (K congruent to 6-7 M-1); moreover, the measured association constants are within experimental error identical with the constant determined for D(Ado)+/Ado (K = 6.0 M-1). This indicates that any coulombic contribution between the -PO3(H)- group and the H+ (N-1) unit of the adenine residue to the stability of the mentioned stacks in D2O is small. However, experiments in 50% (v/v) dioxane-D8/D2O with the D2(5'-AMP) +/- /D(5'-AMP)- 1:1 system reveal, despite its low solubility, that coulombic interactions contribute to the self-association in an environment with a reduced polarity (compared to that of water). The implications of these observations for biological systems are briefly indicated.     

Investigation of the chemical conversion of hydroperoxyeicosatetraenoate to leukotriene epoxide using stereospecifically labeled arachidonic acid. Comparison with the enzymatic reaction

A series of stereospecifically labeled polyunsaturated fatty acids were prepared by biosynthesis from [8-DR-3H]- and [8-LS-3H]stearic acids. The labeled stearic acids were synthesized by a novel scheme employing readily available alkyne and aldehyde starting materials. The stereochemical purity of the prochiral tritium labels was judged to be greater than 99%, as determined by analysis of the octadec-1-yn-8(R)- and 8(S)-ol intermediates in the synthesis. Previously, the labeled arachidonic acids were used to investigate the stereoselectivity of hydrogen abstraction in the biosynthesis of leukotriene epoxides. We have now investigated the selectivity of hydrogen abstraction in a chemical synthesis of 14,15-leukotriene (LT) A4 from mixtures of [3-14C]- and either [10-DR-3H]- or [10-LS-3H]15(S)-HPETE methyl esters. Reaction with either chirally labeled precursor led to 70-95% retention of 3H relative to 14C in the 14,15-LTA4 and 10-Z-14,15-LTA4 products after purification by high performance liquid chromatography. The 15-dienone obtained from this reaction was consistently enriched in 3H relative to 14C after isolation and purification. Evidence was obtained to indicate that the majority of the 3H in the products was retained in its original location and configuration. These results indicate that the biomimetic chemical reaction is stereo-random with respect to hydrogen loss from carbon 10 and that, in contrast to the reaction as it occurs in leukocytes and platelets, in the chemical model the reaction begins by decomposition of the hydroperoxide group, with hydrogen loss from carbon 10 occurring as a late or final step.     

Identification of some metabolic products of 5' -deoxy-5' -S-isobutylthioadenosine, an inhibitor of virus-induced cell transformation.

5' -Deoxy-5' -S-isobutylthioadenosine (iBuS)5' Ado has been shown to be rapidly degraded to 5-deoxy-5-S-isobutylthioribose and adenine in procaryotes. In chick embryo fibroblasts there are two metabolic pathways for (iBuS)5' Ado degradation: (a) oxidative deamination into 5' -deoxy-5'-S-isobutylthioinosine (the main product) and (b) hydrolysis into 5-deoxy-5-S-isobutylthioribose plus adenine. The latter reaction is not due to bacterial contamination, since the same results were obtained under sterile conditions and in chick embryo fibroblasts in culture. The inhibition of the virus-induced cell transformation reported by us previously was due to (iBuS)5' Ado rather than to the main metabolic product of this molecule in chick embryo fibroblasts.     

Synthesis of new mannosyl, galactosyl and glucosyl theophylline nucleosides with potential activity as antagonists of adenosine receptors. DEMA-induced cyclization of glycosylideneiminouracils

The synthesis of D-mannosyl, D-galactosyl and D-glucosyl theophylline nucleosides by diethoxymethyl acetate (DEMA)-induced cyclization of 4-amino-5-glycosylideneimino-1,3-dimethyluracil is reported. 8-Methyltheophylline derivatives of the same sugars were also prepared by Ac(2)O/H(+)-induced cyclization of their imine precursors. This approach has allowed beta-D-mannopyranosyl-, alpha-D-galactofuranosyl- and beta-D-glucofuranosyltheophylline nucleosides to be synthesized for the first time. The inhibition of specific binding at A(1), A(2A), A(2B) and A(3) adenosine receptors in the mannose derivatives is also reported.     

Soluble polymer-supported synthesis of benzodiazepinones

Soluble polymer-supported synthetic method provides a highly efficient route for the construction of biologically important 1,5-benzodiazepin-2-ones. A library of N-substituted benzodiazepinones can be readily assembled utilizing S(N)Ar reaction, reduction of nitro group and one-pot cyclization following N-alkylation as the key step in the synthesis. All reactions in the sequence were performed at room temperature to facilitate the generation of libraries in a parallel fashion. The crude products were obtained in 80-95% yield with 60-96% HPLC purity.     

The photochemistry of 8-bromo-2'-deoxyadenosine. A direct entry to cyclopurine lesions.

The UV photolysis of 8-bromo-2'-deoxyadenosine has been investigated in different solvents and in the presence of additives like halide anions. Photolytic cleavage of the C-Br bond leads to formation of the C8 radical. In methanol, subsequent hydrogen abstraction from the solvent is the main radical reaction; however, in water or acetonitrile intramolecular hydrogen abstraction from the sugar moiety, to give the C5' radical, is the major path. This C5' radical undergoes a cyclization reaction on the adenine and gives the aminyl radical. A rate constant of 1.8 x 10(5) s(-1) has been measured by laser flash photolysis in CH(3)CN for this unimolecular process. Product studies from steady-state photolysis in acetonitrile have shown the conversion of 8-bromo-2'-deoxyadenosine to 5',8-cyclo-2'-deoxyadenosine in 65% yield and in a diastereoisomeric ratio (5' R):(5' S)= 1.7. Evidence supporting that the equilibrium Br*+ Br(-)[right left harpoons] Br(2)*(-) plays an important role in this synthetically useful radical cascade is obtained by regulating the relative concentrations of the two reactive oxidizing species.     

Rapid preparation of the mitotic kinesin Eg5 inhibitor monastrol using controlled microwave-assisted synthesis

We present here a protocol for the synthesis of the dihydropyrimidine (DHPM) derivative monastrol, which is known to be a specific mitotic kinesin Eg5 inhibitor. By applying controlled microwave heating under sealed-vessel conditions, the synthesis via the one-pot three-component Biginelli condensation can be performed in a shorter reaction time (30 min) compared with conventional heating methods that normally require several hours of reflux heating. For the purification of the crude target compound, two different methods are presented. The first protocol includes a simple precipitation/filtration step to provide monastrol in 76% isolated yield and high purity so that no recrystallization step is necessary. This can be ascribed to the microwave heating technology in which less side-product formation is typically one of the advantages. In an alternative purification step, column chromatography is performed, which provides the product in a slightly higher yield (86%). Monastrol synthesis can be conducted in approximately 2 h by employing the precipitation/filtration purification method.     

Improving the Fmoc Solid Phase Synthesis of the Cyclic Hexapeptide Complement C5a Antagonist,PMX205

The anti-inflammatory drug, PMX205, is an antagonist of the C5a complement receptor and has been shown to be effective in rodent models of amyotrophic lateral sclerosis and Alzheimer’s disease. This cyclic hexapeptide (c[Arg-Trp-D-Cha-Pro-Orn]-Hca) has been reported to produce relatively low yields for both the linear peptide assembly and the cyclization reaction in solution and solid phase syntheses. During attempts to reproduce the solid phase methodology, a catastrophic loss of substitution was encountered which could be avoided or reduced by the use of 2-chlorotrityl resin. Likewise, the cyclization reaction could be significantly improved by the use of FDPP (pentafluorophenyl diphenylphosphinate) at high dilution (up to 80% purified yield). Both improvements are accomplished with commercially available products.     

Hydrogen abstraction from thiols by adenosyl radicals: chemical precedent for thiyl radical formation, the first catalytic step in ribonucleoside triphosphate reductase from Lactobacillus leichmannii

Aqueous solutions of adenosylcobalamin (AdoCbl) were thermolyzed with excess beta-mercaptoethanol under anaerobic conditions. The product studies reveal that approximately 90% Co-C bond homolysis occurs, to yield Co(II)cobalamin, 5'-deoxyadenosine, and the disulfide product from the combination of two HOCH2CH2S* radicals, 2,2'-dithiodiethanol; there is also approximately 10% Co-C bond heterolysis, yielding Co(III)cobalamin, adenine, and 2,3-dihydroxy-4-pentenal. The kinetic studies show there is a first-order dependence on AdoCbl and zero-order dependence on thiol under the higher [RSH] experimental conditions used, consistent with the rate-determining step at high [RSH] being the generation of Ado*. The kinetic results require that, in enzyme-free AdoCbl solution, adenosyl radical (Ado*) is formed as a discrete intermediate which then abstracts H* from the added thiol. The activation parameters for Co-C bond homolysis in the presence of thiol trap are the same within experimental error as the activation parameters for Co-C bond homolysis without trap, standard delta H(obs) = 29(2) kcal mol(-1) and standard delta S(obs) = -1(5) e.u. The results, in comparison to the rate of Co-C bond homolysis in ribonucleoside triphosphate reductase (RTPR), reveal that RTPR accelerates Co-C bond cleavage in AdoCbl by approximately 10(10+/-1). The recent literature evidence bearing on the exact mechanism of RTPR enzymic cleavage of the Co-C bond of AdoCbl is briefly discussed, notably the fact that this mechanism is presently controversial, but does involve at least coupled (and possibly concerted) Co-C cleavage, -S-H cleavage, and C-H (Ado-H) formation steps.     

Facile Synthesis of 8, 2′-S-Cyclopurine Nucleoside

Abstract

This paper describes the synthesis of 8,2 -anhydro-8-mercapto-9-(β-D-arabinofuranosyl)purine (8,2′-S-cyclopurinenucleoside, 1) via the shorter route from 3′,5′-di-O-acectyl-8,2′-S-cycloadenosine (6) and by direct reductive deamination with n- pentyl nitrite in tetrahydrofuran (THF) and deacetylation. The preparation of 8,2′-S-cycloadenosine (2) was achieved in good yield by the cyclization of the protected 8-mercaptoadenosine with triphenylphosphine and diethyl azodicarboxylate (DEAD) in THF at room temperature, under Mitsunobu reaction conditions.     

Synthesis of adenosylcobinamide 2-chlorophenyl phosphate,a zwitterionic cobinamide phosphate analog of adenosylcobalamin en route to crystallizable cobinamides

The design and implementation of a new, higher yield synthetic method for synthesizing zwitterionic cobinamide phosphates is described. Adenosylcobinamide 2-chlorophenyl phosphate, beta-AdoCbi-PAr -- a 5,6-dimethylbenzimidazole-free adenosylcobalamin analog, where a 2-chlorophenyl group replaces the ribofuranose and 5,6-dimethylbenzimidazole moieties -- is prepared in tens of milligram quantities, quantities sufficient for crystallization and enzyme trials, amounts 100-fold greater than previously available. The use of (31)P NMR spectroscopy to follow reactions directly, the use of control reactions to learn how to reduce reactant water content, and the use of reaction solvents that completely dissolved the corrinoid reactants were crucial for developing this new synthetic route. beta-AdoCbi-PAr was synthesized in 10% overall isolated yield from cyanocobinamide. Cyanocobinamide was converted to cyanocobinamide 2-chlorophenyl phosphate by direct phosphorylation with 2-chlorophenyl phosphodi-(1,2,4-triazolide) in 25% isolated yield and > or = 98% purity. Sodium borohydride reduction of cyanocobinamide 2-chlorophenyl phosphate and reaction with 5'-chloro-5'-deoxy-adenosine produced beta-AdoCbi-PAr in 42% yield and > or = 98% purity. These compounds were characterized by HPLC, (1)H and (31)P NMR, UV-visible spectroscopy, and liquid secondary ionization mass spectroscopy.     

High yield synthesis of tentoxin, a cyclic tetrapeptide.

Tentoxin is a naturally occurring phytotoxic cyclic tetrapeptide excreted by fungi of the Alternaria alternata family. The four total syntheses of tentoxin published to date give poor total yields, mainly owing to two difficulties, the introduction of the dehydro amino acid and more especially the cyclization step. Here we describe a method that stereospecifically introduces Z-dehydrophenylalanine (deltaZPhe) by a modified Erlenmeyer aldolization reaction. The linear tetrapeptide, Boc-R1Ala-Leu-R2deltaZPhe-G1y-OMe (R1, R2: CH3, 14CH3), the precursor of tentoxin, was obtained in a 72% yield from Boc-Leu-Gly-OH. This linear tetrapeptide, labelled with carbon-14, was used for a comparative study of four cyclization reagents DPPA, DCC-PfpOH, HBTU and HATU. This last was the most effective and gave tentoxin in a 81% cyclization yield. The activated ester formed with this reagent displayed an enhanced capacity for cyclization, permitting cyclization in concentrated medium (10 mM). This new synthetic route gave tentoxin in a 60% yield from Boc-Leu-Gly-OH and offers a means of achieving the synthesis of hitherto elusive analogues.     

Microwave prompted multigram synthesis, structural determination, and photo-antiproliferative activity of fluorinated 4-hydroxyquinolinones

3-Unsubstituted 4-hydroxyquinolin-2(1H)-one containing F and CF(3) substituent in ring is important pharmacological and synthetic target and basic synthones for a number of antibacterial fluoroquinolones and is promising potent and selective glycine site NMDA receptors. A simple facile one-step microwave enhanced multigram synthesis of such fluorinated quinolones in reasonable purity has been developed in excellent yield (85-94%) in 3-5 min, whereas conventional synthesis required the harsh conditions, long reaction period with use of environmentally unacceptable regents giving the required product in lower yield. The phototoxicity as well as the cytotoxic activities of the title compounds are evaluated against leukemia- and adenocarcinoma-derived cell lines in comparison to the normal human keratinocytes. Structure-activity relationships between the chemical structures and the antimycobacterial, antifungal activity of the evaluated compounds are also discussed.     

Synthesis of (6Z,9Z,11E)-octadecatrienoic and (8Z,11Z,13E)-eicosatrienoic acids and their [1-(14)C]-radiolabeled analogs

In order to study the metabolic pathway and the physiological effects of 9c,11t-18:2 (major isomer of conjugated linoleic acid) and its C(18:3) and C(20:3) metabolites, 6c,9c,11t-18:3 and 8c,11c,13t-20:3 and their [1-(14)C]-radiolabeled analogs were prepared stereoselectively by total synthesis. The 8c,11c,13t-20:3 was obtained in 11 steps. The synthesis involves a highly stereoselective Wittig reaction between 3-(t-butyldiphenylsilyloxy)propanal and the ylide of 7-(2-tetrahydropyranyloxy)heptanylphosphonium salt which gave (3Z)-1-(t-butyldiphenylsilyloxy)-10-(2-tetrahydropyranyloxy)dec-3-ene in a first step. Then the t-butyldiphenylsilyl derivative was deprotected selectively and the resulting alcohol function was converted via a bromide into a phosphonium salt. The second stereoselective Wittig condensation between the phosphonium salt and commercial (2E)-non-2-enal under cis-olefinic conditions using Lithium hexamethyldisilazide as base afforded the (7Z,10Z,12E)-1-(2-tetrahydropyranyloxy)nonadeca-7,10,12-triene in a very good isomeric purity. The intermediate product was brominated and transformed by reaction with magnesium into Grignard reagent, which was one-carbon elongated by unlabeled or labeled carbon dioxide to obtain the 8c,11c,13t-20:3 in good isomeric purity (95%) and high radiochemical purity for its [1-(14)C]-radiolabeled analog (99%). 6c,9c,11t-18:3 was synthesized in a similar way by using 5-(2-tetrahydropyranyloxy)pentanylphosphonium salt in place of 7-(2-tetrahydropyranyloxy)heptanylphosphonium salt in a first step. Other reactions were unchanged and products were obtained in similar yields. Similar to 8c,11c,13t-20:3, the 6c,9c,11t-18:3 was obtained in a very good isomeric purity (95%) and its [1-(14)C]-radiolabeled analog in a high radiochemical purity (95%).     

On the synthesis of orexin A: a novel one-step procedure to obtain peptides with two intramolecular disulphide bonds.

An efficient strategy for the synthesis of orexin A, a recently discovered neuropeptide with two intramolecular disulphide bonds, was developed. Four different methods for the synthesis of peptides containing two disulphide bonds were compared and optimized with respect to reaction time, purity of the crude peptide and yield of the purified peptide. A new one-step cyclization method in solution is presented for fast, easy and high yield synthesis of orexin A, based on iodine oxidation in acetic acid/water and S-acetamidomethyl (S-Acm) and S-trityl (S-Trt) for side-chain protection of cysteine. Disulphide formation without selective side-chain protection leads to the formation of different mono- and bicyclic configurations of orexin A. These data stress the requirement of selective cysteine side-chain protection in the synthesis of orexin A.     

CH(3)ReO(3)-catalyzed oxidation of cholesta-5,7-dien-3beta-yl acetate with the urea-hydrogen peroxide adduct under various conditions. Synthesis of the natural epoxy sterol 9alpha,11alpha-epoxy-5alpha-cholest-7-en-3beta,5,6beta-triol

This article describes the oxidation of cholesta-5,7-dien-3beta-yl acetate (4) with the urea-hydrogen peroxide adduct (UHP) using methyltrioxorhenium (MTO) as catalyst, under various conditions. Specifically, the effects of using different solvents (CHCl(3) and ethers) and additives (EtOH and pyridine) on the course of the MTO-catalyzed oxidation of 4 were investigated. Some new steroids (6, 9, 10 and 11), obtained from this oxidation, were isolated and characterized on the basis of chemical evidence and interpretation of spectroscopic data including H-H COSY and HMBC experiments. The optimal solvent for the oxidation of 4 with MTO/UHP oxidizing system was diethyl ether. In this solvent the reaction is clean and gave as the main product 5,6beta-dihydroxy-5alpha-cholest-7-en-3beta-yl acetate (8, 65% yield), obtained with a more simple procedure and with a higher yield than that reported in literature. Sterol 8 is a key intermediate compound in the synthesis of many steroids of marine origin, biologically active, oxygenated at the B/C rings. In fact, starting from diol 8, we performed the synthesis of the natural cytotoxic epoxy sterol 9alpha,11alpha-epoxy-5alpha-cholest-7-en-3beta,5,6beta-triol (15, 21% yield) with an improvement in yield and number of steps over a synthesis of the same natural product previously reported. When the oxidation of 4 with the MTO/UHP system in diethyl ether was performed in the presence of pyridine as ligand, the unsaturated epoxide 5,6alpha-epoxy-5alpha-cholest-7-en-3beta-yl acetate (10, 90% yield) was obtained after only 5 min in good yield. In fact, pyridine, besides having beneficial effect on the reaction rate, shuts down the ring opening reactions, as reported in literature.     

Shaken not stirred: a facile synthesis of 1,4-bis(furo[2,3-d]-pyrimidine-2,4(1H,3H)-dione-5-yl)benzenes by one-pot reaction of isocyanides, N,N'-dimethylbarbituric acid, and terephthaldialdehyde

A simple and efficient synthesis of 1,4-bis(furo[2,3-d]pyrimidine-2,4(1H,3H)-dione-5-yl)benzene derivatives was achieved via a one-pot three-component reaction of isocyanides, N,N'-dimethylbarbituric acid, and terephthaldialdehyde in DMF at room temperature for 30 min. These improved reaction conditions allow the preparation of highly substituted furopyrimidinones in high yields and purity under mild reaction conditions.     

Hemes and hemoproteins. 5: Kinetics of the peroxidatic activity of microperoxidase-8: model for the peroxidase enzymes

The peroxidatic activity of the heme octapeptide from cytochrome c, microperoxidase-8 (MP-8), was assayed at 25 degrees C under conditions where formation of Compound I is rate limiting. In the pH range 6-9, the reaction rate increased linearly with a slope close to unity. The active form of the substrate is the hydroperoxide anion, HO2-, and an extrapolated second-order rate constant was obtained for the reaction of aquoMP-8 with HO2- of 3.7 X 10(8) M-1 sec-1, which is close to the second-order rate constants reported for reaction of the peroxidase enzymes with H2O2. Comparison with published data shows that the Fe3+ ion of MP-8 reacts as expected with simple anions, electrons, and HO2-, while the analogous reactions of the enzymes all show a requirement for one H+. We conclude that the peroxidase enzymes activate H2O2 under physiological conditions through a pH-independent, H+-coupled binding of the required H2O2-. The peroxidase activity of MP-8 can be increased more than tenfold by the presence of the guanidinium ion, which is ascribed to formation of the ion-pair GuaH+HO2-; this suggests a role for the invariant distal Arg in the enzymes.     

Thermodynamic and structural characterization of cis-trans isomerization of 12-(S)-hydroxy-(5Z, 8E, 10E)-heptadecatrienoic acid by high-performance liquid chromatography and gaschromatography-mass spectrometry.

It is shown that 12-(S)-hydroxy-(5Z, 8E, 10E)-heptadecatrienoic acid (5-cis-HHT)--a physiological metabolite of arachidonic acid--is acid-catalyzed converted into a less polar substance with its maximum UV-absorption at (1)max=232 nm and a molar absorptivity of about epsilon=26600 +/- 200 M(-1)cm(-1). Using a reversed-phase high-performance liquid chromatographic (HPLC) method this equilibrium reaction (K(c) = 1.78 +/- 0.05 at pH 1.10 and 298 K) could be thermodynamicly characterized as a pH dependent, exergonic and exothermic reaction according to kinetics of a first order reaction (at pH 1.10 and 298 K: delta(R)G(o) = -1.42 +/- 0.07 kJ mol(-1), delta(R)H(o) = -3.50 +/- 0.9 kJ mol(-1), delta(R)S(o) = 7.0 +/- 3.0 J mol(-1)*K, delta(R)H*f = 100.0 +/- 4.0 kJ mol(-1)). Kinetic data for several pH-values and temperatures are presented. These data and structural characterization by gaschromatography-mass spectrometry (GC/MS) lead to the conclusion that 5-cis-HHT is isomerized to 12-(S)-hydroxy-(5E, 8E, 10E)-heptadecatrienoic acid (5-trans-HHT).