Rhizobial saccharides. Part. 4. Unusual Reactivity of Pyruvated Glycosyl Donors during construction of rhizobial exopolysaccharide fragments

Two pyruvated galactosyl donors, 2,3-di-O-benzoyl-4,6-O-[1-(R)-methoxycarbonyl(ethylidene)]-α-D -galactopyranosyl chloride ( 6 ) and trichloroacetimidate 13 , were coupled to position 3 of suitably protected mono and disaccharide benzyl glucoside acceptors. For both donors, an unusual high content of the α-(1 → 3)-linked products was obtained. The corresponding β-(1 → 3)-linked di- and trisaccharides are related to exopolysaccharides of Rhizobium leguminosarum.     

1-β-D-arabinofuranosylcytosine conjugates of ether and thioether phospholipids. A new class of ara-C prodrug with improved antitumor activity

The 1-β-D-arabinofuranosylcytosine (ara-C) conjugates 1-O-alkyl (ether) and 1-S-alkyl (thioether) phospholipids, being analogues of ara-CDP-sn-1,2-O-dipalmitoylglycerol (1), showed significant antitumor activity against L1210 and P388 leukemiain vivo. The more active conjugates include the 1-O-alkyl analogues, ara-CDP-rac-1-O-hexadecyl-2-O-palmitoylglycerol (2) and ara-CDP-rac-1-O-octadecyl-2-O-palmitoylglycerol (3), and the corresponding 1-S-alkyl analogues, ara-CDP-rac-1-S-hexadecyl-2-O-palmitoyl-1-thioglycerol (4) and ara-CDP-rac-1-S-octadecyl-2-O-palmitoyl-1-thioglycerol (5, Cytoros). The conjugates were formulated by sonication, in which the conjugates existed as discs (size 0.01–0.04 μ).. Among the conjugates of the three different phospholipids, the 1-S-alkyl analogues 4 and 5 displayed the strongest antitumor activity against L1210 leukemia in mice, followed by the 1-O-alkyl (2 and 3) and the 1-O-acyl (1) analogues. The 1-S-alkyl analogue 5 was considerably more effective than the 1-O-acyl analogue 1 against myelomonocytic WEHI-3B leukemia in mice. Conjugate 5 (Cytoros) showed a significant therapeutic activity in mice with colon 26 carcinoma, M5076 sarcoma, and C-1300 neuroblastoma. Furthermore, this agent inhibited liver metastases of M5076 sarcoma. Conjugates 3 and 5 also inhibited the metastasis of 3-Lewis lung carcinoma to the lungs of mice. Cytoros (5) and its analogues, with other ether and thioether phospholipids, appear to offer increased therapeutic benefit to mice with tumors. Based on a paper presented at the Third International Conference on Platelet-Activating Factor and Structurally Related Alkyl Ether Lipids, Tokyo, Japan, May 1989.     

The First Total Syntheses of Enantiomerically Pure Naturally Occuring Ellagitannins Gemin D and its Regioisomer Hippomanin A

The total syntheses of naturally occuring ellagitannins gemin D ( 1 ) and its regioisomer hippomanin A ( 2 ) are reported. In addition, the phase-transfer catalyzed benzylation reaction of the 2,3-glucopyranoside diols 3–7 is described. Our studies have illustrated the influence of the structure of 2,3-glucopyranoside diols on the regioselectivity of the phase-transfer catalyzed benzylation at their free 2,3-OH groups. We could show, that both phase-transfer catalyzed benzylations of 2,3-glucopyranoside diols using tetrabutyl-ammonium hydrogensulfate (Bu4NHSO4) or using tetrabutylammonium iodide (Bu4NI) disfavour the formation of the corresponding 3-O-monobenzylated products and preferrentially give the 2- O-monobenzylated products. However, the ratio of the generated 2- versus 3-O-mono- and 2,3-dibenzylated products from these reactions also strongly depends upon the nature of the starting materials. The glucopyranosides 3 and 4 are the first examples, which allow the completely regioselective monobenzylation at the 2-OH positions by a phase-transfer catalyzed reaction.     

1-O-alkyl-linked phosphoglycerides of human platelets: Distribution of arachidonate and other acyl residues in the ether-linked and diacyl species

In this study, the 1-O-alkyl-2-acyl-sn-glycero-3-phosphocholine content of human platelets was determined. The distribution of arachidonate among the 1,2-diacyl, 1-O-alkyl-2-acyl, and 1-O-alk-l′-enyl-2-acyl classes of choline- and ethanolamine-containing phosphoglycerides was also assessed. The major platelet phospholipids were choline-containing phosphoglycerides (38%), ethanolamine-containing phosphoglycerides (25%) and sphingomyelin (18%), with smaller amounts of phosphatidylserine (11%) and phosphatidylinositol (4%). In addition to the diacyl class, the choline-linked fraction was found to contain both 1-O-alkyl-2-acyl (10%) and 1-O-alk-l′-enyl-2-acyl (9%) species. The ethanolamine-linked fraction, on the other hand, had an elevated level of the 1-O-alk-l′-enyl-2-acyl (60%) species and a small amount of the 1-O-alkyl-2-acyl component (4%). The major fatty acyl residues found in all classes of the choline and ethanolamine phospholipids were 16∶0, 18∶0, (Δ⁹), 18∶2(n−6) and 20∶4(n−6). The 1-O-alk-l and 1-O-alk-l′-enyl fraction of the ethanolamine-linked phospholipids also contained substantial amounts of 22∶4(n−6), 22∶5(n−3) and 22∶6(n−3) acyl chains. Arachidonate comprised 44% of the acyl residues in thesn-2 position of 1-O-alkyl-2-acyl-sn-glycero-3-phosphocholine. Corresponding values for the diacyl and 1-O-alk-l′-enyl-2-acyl species were 23% and 25%, respectively, based on all 20∶4(n−6) being linked to thesn-2 position of all classes. In the ethanolamine-linked phosphoglycerides, arachidonate constituted 60%, 20% and 68% of the acyl groups in thesn-2 position of the 1,2-diacyl, 1-O-alkyl-2-acyl and 1-O-alk-l′-enyl-2-acyl classes, respectively. The content of 1-O-alkyl-2-acyl-sn-glycero-3-phosphocholine appears sufficient to support the synthesis of platelet activating factor by a deacylation-reacylation pathway in platelets. Our findings also demonstrate that human platelets contain a significant amount of 1-O-alkyl-2-arachidonyl-sn-glycero-3-phosphocholine that could possibly serve as a precursor of both platelet activating factor and bioactive arachidonate metabolites.     

1-O-alkyl-2-(ω-oxo)acyl-sn-glycerols from shark oil and human milk fat are potential precursors of PAF mimics and GHB

This study examines the feasibility that peroxidation and lipolysis of 1-O-alkyl-2,3-diacyl-sn-glycerols (DAGE) found in shark liver oil and human milk fat constitutes a potential source of dietary precursors of platelet activating factor (PAF) mimics and of gamma-hydroxybutyrate (GHB). Purified DAGE were converted into 1-O-alkyl-2-acyl-sn-glycerols by pancreatic lipase, without isomerization, and transformed into 1-O-alkyl-2-oxoacyl-sn-glycerols by mild autooxidation. The various core aldehydes without derivatization, as well as the corresponding dinitrophenylhydrazones, were characterized by chromatographic retention time and diagnostic ions by online electrospray mass spectrometry. Core aldehydes of oxidized shark liver oil yielded 23 molecular species of 1-O-alkyl-sn-glycerols with short-chain sn-2 oxoacyl groups, ranging from 4 to 13 carbons, some unsaturated. Autooxidation of human milk fat yielded 1-O-octadecyl-2-(9-oxo)nonanoyl-sn-glycerol, as the major core aldehyde. Because diradylglycerols with short fatty chains are absorbed in the intestine and react with cytidine diphosphate-choline in the enterocytes, it is concluded that formation of such PAF mimics as 1-O-alkyl-2-(ω-oxo)acyl-sn-glycerophosphocholine from unsaturated dietary DAGE is a realistic possibility. Likewise, a C₄ core alcohol produced by aldol-keto reduction of a C₄ core aldehyde constitutes a dietary precursor of the neuromodulator and recreational drug GHB, which has not been previously pointed out.     

O-alkyl diolO-,S- andSe-phosphoroamidates of DL-α-tocopherol and their dimethylaminoalkyl derivatives as diester and triester models of phospholipids

Hexamethyltriamide of phosphorous acid, activated by addition of iodine at an optimal molar ratio of 1.05∶0.05, was used as a phosphorylating reagent to synthesize 1-hexadecyloxyethyl-2-O-, 1-hexadecyloxypropyl-3-O-, and 1-hexadecyloxybutyl-4-O-(DL-α-tocopheryl-6-O)-(N,N-dimethylamido)selenophosphate,-thiophosphate and-phosphate derivatives, and some of their 2-dimethyl-aminoethyl-1-O-, and 3-dimethylaminopropyl-1-O-triester analogues in a “one-pot procedure” in overall yields of 69–87%. Activation of the reaction with an equimolar mixture of imidazole and carbon disulfide at the triester formation step permits selective phosphorylation at room temperature. The compounds synthesized represent new diester and triester models containing alkyl ether diolphospholipid structures.     

New glyceroglycolipid and ceramide from <Emphasis Type="Italic">Premna microphylla</Emphasis>

Iwo new compounds (1,2) were isolated from the ethanolic extract of the leaves of Premna microphylla, together with five known compounds. The structures of compounds 1 and 2 were elucidated as (2S,3S,4R,11E)-2-[(2R)-2-hydroxytetracosanoylamino]-11-octadecene-1,3,4-triol (1) and 1-O(9Z,12Z, 15Z-octadecatrienoyl)-3-O-[β-d-galactopyranosyl-(1→6)-O-β-d-galactopyranosyl-(1→6)-α-d-galactopyranosyl] glycerol (2) by means of spectroscopic and chemical methods.     

Further studies on sphingolipids in wheat grain

The principal molecular species of sphingolipids in wheat grain were confirmed to beN-2′-hydroxylignoceroyl-4-hydroxysphinganine for ceramide, and 1-O-β-glucosyl-, 1-O-[β-mannosyl(1→4)-O-β-glucosyl]-, 1-O-[β-mannosyl(1→4)-O-β-mannosyl(1→4)-O-β-glucosyl]-and 1-O[β-mannosyl(1→4)-O-β-mannosyl(1→4)-O-β-mannosyl(1→4)-O-β-glucosyl]-N-2′-hydroxypalmitoyl (or hydroxyarachidoyl)-cis-8-sphingenine for mono-, di-, tri- and tetraglycosylceramide, respectively. A novel glycolipid, cellobiosylceramide, was found as the minor diglycosylceramide; the major species was characterized to be 1-O-[β-glucosyl(1→4)-O-β-glucosyl]-N-2′-hydroxypalmitoyl (or hydroxyarachidoyl)-cis-8-sphingenine. It was observed in these sphingolipids that the dihydroxy bases were combined mainly with C₁₆ and C₂₀ acids, whereas the trihydroxy bases combined mostly with acids of chain length of 20 or more.     

Synthesis of trideuteratedO-alkyl platelet activating factor and lyso derivatives

Racemic heavy isotope analogs of 1-O-alkyl-sn-glycero-3-phosphocholine (lysoPAF) and 1-O-alkyl-2-O-acetyl-sn-glycero-3-phosphocholine (PAF) were prepared for use as internal standards to facilitate quantitative studies based on mass spectrometry. Starting from pentadencane-1,15-diol andrac-glycerol-1,2-acetonide, a convergent synthesis of 1-O-[16′-²H₃]hexadecyl and 1-O-[18′-²H₃]octadecylrac-glycero-3-phosphocholine and their acetyl derivatives is described. Three deuterium atoms were introduced at the terminal position of the 1-O-alkyl group by displacement of thep-toluensulfonyl group from 1-O-alkyl-15′-p-toluensulfonate and 1-O-alkyl-17′-p-toluensulfonate with [²H₃]-methylmagnesium iodide. The 1-O-alkyl-17′-p-toluensulfonate was obtained by reaction of the 1-O-alkyl-15′-p-toluensulfonate with allylmagnesium bromide, followed by reductive ozonolysis and treatment withp-toluenesulfonyl chloride. The hydroxyl group at C-2 was protected by a benzyl group and removed at a late stage in the synthesis. This provided the corresponding lysoderivatives or allowed preparation of racemic PAF by subsequent acetylation of the free hydroxy group. The phosphocholine moiety was introduced at glycerol C-3 by reaction with bromoethyldichlorophosphate and trimethylamine. The synthetic compounds were analyzed by FAB/MS and GC/NICIMS. They were shown to contain less than 0.6% protium impurity.     

Oxidation of 1-O-(alk-1-enyl)-2,3-di-O-acylglycerols: Models for plasmalogen oxidation

Alk-1-enyl diacyl glycerides, model compounds for plasmalogen lipids, were synthesized for use as substrates in oxidation studies. The neutral plasmalogen glycerides prepared included 1-O-(hexadec-1-enyl)-2,3-di-O-stearoylglycerol (4a) and 1-O-(hexadec-1-enyl)-2-O-linoleoyl-3-O-stearoylglycerol (4b). Oxidative disappearance of these glycerides was followed directly by high performance liquid chromatography (HPLC). The extent of oxidation of the side chains of these glycerides, i.e. the alkenyl ether and fatty acyl functions, was monitored by conversion of the side chains to dimethylacetal and methyl ester by methanolysis, followed by subsequent gas chromatography (GC) of the methanolysis products. Both analytical approaches show that the alkenyl ether function of neat4a oxidizes more slowly than neat ethyl linoleate. However, the rate of alkenyl ether loss from4a is accelerated in the presence of added ethyl linoleate. Moreover, when the linoleoyl group is incorporated into the 2-position of the alkenyl glyceride, as in4b, the rate of loss of the alkenyl group was shown to be similar to the rate of loss of the linoleoyl group. These results suggest that oxidation of plasmalogen glycerides should not be ignored as a factor that contributes to the oxidative instability of animal tissue. Presented in part at the American Oil Chemists' Society 77th Annual Meeting, Honolulu, HI, May 1986.     

Lyso platelet activating factor (LysoPAF) and its enantiomer. Total synthesis and carbon-13 NMR spectroscopy

Described is a reaction sequence for the total synthesis of lyso platelet activating factor (lysoPAF; 1-O-alkyl-sn-glycero-3-phosphocholine) and its enantiomer. The procedure is versatile and yields optically pure isomers of defined chain length. The synthesis is equally suited for the preparation of lysoPAF analogues and its enantiomers with unsaturation in the long aliphatic chain. First,rac-1(3)-O-alkylglycerol is prepared by alkylation ofrac-isopropylideneglycerol with alkyl methanesulfonate followed by acid-catalyzed removal of the ketal group. The primary hydroxy group of alkylglycerol is then protected by tritylation, the secondary hydroxy group is acylated, and the protective trityl group is removed under mild acidic conditions with boric acid on silicic acid, essentially without acyl migration. Condensation of the diradylglycerol with bromoethyl dichlorophosphate in diethyl ether, hydrolysis of the resulting chloride, and nucleophilic displacement of the bromine with trimethylamine givesrac-1-O-alkyl-2-acylglycero-3-phosphocholine in good overall yield. The racemic alkylacylglycerophosphocholine is finally treated with snake venom phospholipase A₂ (Ophiophagus hannah) which affords 1-O-alkyl-sn-glycero-3-phosphocholine (lysoPAF) of natural configuration in optically pure form. The “unnatural” 3-O-alkyl-2-O-acyl-sn-glycerol-1-phosphocholine enantiomer, which is not susceptible to phospholipase A₂ cleavage, gives 3-O-alkyl-sn-glycero-1-phosphocholine upon deacylation with methanolic sodium hydroxide. Homogeneity and structure of the intermediates and final products were ascertained by carbon-13 nuclear magnetic resonance spectroscopy on monomeric solutions.     

Synthesis of three tethered trisaccharides to probe entropy contributions in carbohydrate—protein interactions

Crystal structure data show that the branched trisaccharide 1 constitutes the complete antigenic determinant of the Salmonella serogroup B antigen that is recognized by monoclonal antibody SE155.4. In an effort to characterize the entropic costs associated with immobilization of glycosidic torsional angles in the bound state, three distinct intramolecularly tethered analogues of this trisaccharide 2-4 have been synthesized. Two trisaccharides are tethered by a methylene acetal via the O-2 position of the 3,6-dideoxy-hexose, abequose to either O-2 of galactose ( 2 ) or O-4 of mannose ( 3 ). The third tether, α,α′-di-thio-p-xylene, spans the C-6 atoms of the mannose and galactose residues to create trisaccharide 4 . The acetal tethers of 2 and 3 span hydroxyl centers that are known to be involved in intramolecular sugar-sugar hydrogens bonds, but both trisaccharides are biologically inactive due to distorted conformations that cannot be accommodated in the antibody binding site. Trisaccharide 4 is active since both hydroxymethyl groups of galactose and mannose are solvent exposed in the bound state and the constrained conformation of 4 is virtually superimposable on the bound conformation of 1 . Despite the retained complimentary and significant reduction of torsional flexibility, trisaccharide 4 exhibits a ΔG° = -7.6 kcal mol⁻¹ compared to ΔG° = -7.1 kcal mol⁻¹ for 1 . The modest free energy gain for the tethered trisaccharide 4 arises from a small entropy gain (TΔΔS = 0.3 kcal mol⁻¹) and an even smaller enthalpic change (ΔΔH = -0.2 kcal mol⁻¹).     

Isolation of Ingenol-Type Diterpenoids from Euphorbia kansui by Offline Coupling of HPLC-ESI-MSn and HSCCC

A method based on an offline coupling of high-performance liquid chromatography/electrospray ionization multi-stage mass spectrometry (HPLC-ESI-MSⁿ) and high-speed counter-current chromatography (HSCCC), was established for targeted separation and purification of skin-irritative and structurally similar ingenol-type diterpenoids in Euphorbia kansui. The crude dichloromethane extract of Euphorbia kansui after an initial clean-up step on silica gel and targeted fractionation according to HPLC-ESI-MSⁿ, was separated by HSCCC. As a result, 3-O-(2′E,4′Z-decadienoyl)-20-O-acetylingenol and 3-O-(2′E,4′E-decadienoyl)-20-O-acetylingenol as well as a pair of geometrical isomers, 5-O-(2′E,4′Z-decadienoyl)-20-O-acetylingenol and 5-O-(2′E,4′E-decadienoyl)-20-O-acetylingenol, were successfully separated and purified. The established method is rapid and efficient without irritation to operators, providing an extensible and feasible way for the separation and purification of other toxic and skin-irritative compounds.     

Two New Monogalactosyl Diacylglycerols from Brown Alga <Emphasis Type="Italic">Sargassum thunbergii</Emphasis>

Two new monogalactosyl diacylglycerols (MGDGs) along with two known glycolipids were isolated from the moderate polar fraction of the methanolic extract of the brown alga Sargassum thunbergii by using reversed silica flash chromatography. Two new MGDGs were identified as (2S)-1-O-(5Z,8Z,11Z,14Z,17Z-eicosapentaenoyl)-2-O-(9Z,12Z,15Z-octadecatrienoyl)-3-O-β-d-galactopyranosyl-sn-glycerol (1) and (2S)-1-O-(9Z,12Z,15Z-octadecatrienoyl)-2-O-(6Z,9Z,12Z,15Z-octadecatetraenoyl)-3-O-β-d-galactopyranosyl-sn-glycerol (2) by FAB tandem mass spectrometry, NMR techniques, and specific enzyme-catalyzed hydrolysis of the sn-1 fatty acyl linkage. The regiochemical attachment of the acyl chains in the glycerol moiety was established by 2D NMR correlations and confirmed by enzymatic hydrolysis.     

Non-Chlorine Bleaching of Kraft Pulp II. Ozonation of Methyl 4-O-Ethyl-β-D-glucopyranoside (1) Preparation of Authentic Carbonyl Sugars and Their Analysis by Gas Chromatography and Mass Spectrometry

Methyl 4-O-ethyl-β-D-glucopyranoside (1) was prepared as a model compound for cellulose to investigate the reactions of ozone with polysaccharides during ozone bleaching of kraft pulp. The model compound was converted into authentic carbonyl sugars, methyl 3,6-di-O-acetyl-4-O-ethyl-β-D-arabino-hexopyranosidulose (2), methyl 2,6-di-O-acetyl-4-O-ethyl-β-D-ribo-hexopyranoside-3-ulose (3), methyl 2,3-di-O-acetyl-4-O-ethyl-β-D-gluco-hexodialdo-1,5-pyranoside (4). These carbonyl sugars were converted into O-methyloximes and analyzed by gas chromatography and mass spectrometry.     

New cerebrosides from the basidiomycete <Emphasis Type="Italic">Cortinarius tenuipes</Emphasis>

Five cerebrosides (1–5), including three new ones named cortenuamide A (1), cortenuamide B (2), and cortenuamide C (3), were isolated from the fruiting bodies of the basid-iomycete Cortinarius tenuipes. The structures of those compounds were elucidated as (4E,8E)-N-d-2′-hydroxytetracosanoyl-1-O-β-d-glycopyranosyl-9-methyl-4,8-sphingadienine (1), (4E,8E)-N-d-2′-hydroxytricosanoyl-1-O-β-d-glycopyranosyl-9-methyl-4,8 sphingadienine (2), (4E, 8E)-N-d-2′-hydroxydocosanoyl-1-O-β-d-glycopyranosyl-9-methyl-4,8-sphingadienine (3), (4E, 8E)-N-d-2′-hydroxyoctadecanoyl-1-O-β-d-glycopyranosyl-9-methyl-4,8-sphingadienine (4), and (4E, 8E)-N-d-2′-hydroxypalmitoyl-1-O-β-d-glycopyranosyl-9-methyl-4,8-sphingadienine (5) by spectral and chemical methods.     

Structure-Based Design,Synthesis, and Biological Evaluation of Imidazo[4,5-b]Pyridin-2-one-Based p38 MAP Kinase Inhibitors: Part 2

We identified novel potent inhibitors of p38 mitogen-activated protein (MAP) kinase using a structure-based design strategy, beginning with lead compound, 3-(butan-2-yl)-6-(2,4-difluoroanilino)-1,3-dihydro-2H-imidazo[4,5-b]pyridin-2-one ( 1 ). To enhance the inhibitory activity of 1 against production of tumor necrosis factor-α (TNF-α) in human whole blood (hWB) cell assays, we designed and synthesized hybrid compounds in which the imidazo[4,5-b]pyridin-2-one core was successfully linked with the p-methylbenzamide fragment. Among the compounds evaluated, 3-(3-tert-butyl-2-oxo-2,3-dihydro-1H-imidazo[4,5-b]pyridin-6-yl)-4-methyl-N-(1-methyl-1H-pyrazol-3-yl)benzamide ( 25 ) exhibited potent p38 inhibition, superior suppression of TNF-α production in hWB cells, and also significant in vivo efficacy in a rat model of collagen-induced arthritis (CIA). In this paper, we report the discovery of potent, selective, and orally bioavailable imidazo[4,5-b]pyridin-2-one-based p38 MAP kinase inhibitors.     

Pyridine-2(1H)-thione in heterocyclic synthesis: synthesis and antimicrobial activity of some new thio-substituted ethyl nicotinate,thieno[2,3-b]pyridine and pyridothienopyrimidine derivatives

3-(4-Bromophenyl)-2-cyanoprop-2-enethioamide (1) reacted with ethyl 3-oxo-3-phenylpropanoate (2) to give ethyl 4-(4-bromophenyl)-5-cyano-2-phenyl-6-thioxo-1,6-dihydropyridine-3-carboxylate (3). Compound 3 was taken as a starting material for the synthesis of thio-substituted ethyl nicotinate derivatives 5a–d, which underwent cyclization to the corresponding thieno[2,3-b]pyridines 6a–d. Also 3 reacted with hydrazine hydrate to give the pyrazolo[3,4-b]pyridine derivative 7, which upon diazotization gave the diazonium derivative 8. Compound 6a condensed with dimethylformamide–dimethylacetal to afford thieno[2,3-b]pyridine derivative 9, which reacted with different amines 10a–e to afford the pyridothienopyrimidine derivatives 12a–e through the Dimroth rearrangement. Moreover, compound 6a reacted with different reagents to give pyridothienopyrimidine derivatives 14a and b, 17 and pyrazolothienopyridine derivative 18. In addition, acetylating compound 6c with chloroacetylchloride afforded the 3-[(2)-chloroacetylamino]thieno[2,3-b]pyridine derivative 20, which upon cyclization yielded the corresponding 2-chloromethylpyrido[3′,2′:4,5]thieno[3,2-d]pyrimidine derivative 21. Some of the newly synthesized compounds were screened in vitro for their antimicrobial activities.

     

Optimization of LpxC Inhibitors for Antibacterial Activity and Cardiovascular Safety

UDP-3-O-(R-3-hydroxymyristoyl)-N-acetylglucosamine deacetylase (LpxC) is a Zn²⁺ deacetylase that is essential for the survival of most pathogenic Gram-negative bacteria. ACHN-975 (N-((S)-3-amino-1-(hydroxyamino)-3-methyl-1-oxobutan-2-yl)-4-(((1R,2R)-2-(hydroxymethyl)cyclopropyl)buta-1,3-diyn-1-yl)benzamide) was the first LpxC inhibitor to reach human clinical testing and was discovered to have a dose-limiting cardiovascular toxicity of transient hypotension without compensatory tachycardia. Herein we report the effort beyond ACHN-975 to discover LpxC inhibitors optimized for enzyme potency, antibacterial activity, pharmacokinetics, and cardiovascular safety. Based on its overall profile, compound 26 (LPXC-516, (S)-N-(2-(hydroxyamino)-1-(3-methoxy-1,1-dioxidothietan-3-yl)-2-oxoethyl)-4-(6-hydroxyhexa-1,3-diyn-1-yl)benzamide) was chosen for further development. A phosphate prodrug of 26 was developed that provided a solubility of >30 mg mL⁻¹ for parenteral administration and conversion into the active drug with a t_1/2 of approximately two minutes. Unexpectedly, and despite our optimization efforts, the prodrug of 26 still possesses a therapeutic window insufficient to support further clinical development.     

A new diacylgalactolipid containing 4Z-16∶1 from the marine cyanobacterium Oscillatoria sp

A new diacylgalactolipid was isolated from the marine cyanobacterium Oscillatoria sp., and the structure was elucidated as (2S)-3-O-β-d-galactopyranosyl-1-O-(9Z,12Z-octadecadienoyl)-2-O-(4Z-hexadecenoyl)glycerol by enzymatic partial hydrolysis using lipase and physicochemical evidence, which included determining the double bond position in the hexadecenoic acid moiety.