Design,synthesis, and evaluation of water-soluble phospholipid analogues as inhibitors of phospholipase C from Bacillus cereus

The rate of hydrolysis of natural phospholipids by the phosphatidylcholine-preferring phospholipase C from Bacillus cereus (PLC(Bc)) follows the order phosphatidylcholine > phosphatidylethanolamine > phosphatidyl-l-serine. To probe the structural basis for this substrate specificity, a series of water-soluble, nonhydrolyzable substrate analogues were needed so their complexes with the enzyme could be studied via X-ray crystallography and isothermal titration calorimetry (ITC). Accordingly the water-soluble dithiophospholipids 2-10 having choline, ethanolamine, and l-serine headgroups were synthesized, and the inhibitory activity of each was determined in an assay using 1,2-dihexanoyl-sn-glycero-3-phosphocholine (C6PC) as the monomeric substrate. The 1,2-dibutanoyl dithiophosphocholine 2 was a weak inhibitor, whereas the related 1,2-dipentanoyl dithiophosphocholine 3 and the ethylene glycol dithiophosphocholines 4 and 5 were moderate inhibitors. The 1,2-omega-hydroxydiacyl dithiophosphocholines 6 and 7 were potent inhibitors, while the related compound 8, which had shorter acyl side chains, was a weak inhibitor. The dithiophosphoethanolamine 9 was a modest inhibitor, whereas the dithiophospho-l-serine 10 was a somewhat weaker inhibitor. Overall, the phospholipid analogues had increasing K(i) values according to the order 2 < 10 < 3 < 4 approximately 5 approximately 8 < 9 < 6 < 7 and increasing solubility according to the sequence 5 approximately 7 < 4 approximately 6 approximately 9 < 3 < 10 < 8 < 2.     

C6-C8 bridged epothilones: consequences of installing a conformational lock at the edge of the macrocycle

A series of conformationally restrained epothilone analogues with a short bridge between the methyl groups at C6 and C8 was designed to mimic the binding pose assigned to our recently reported EpoA-microtubule binding model. A versatile synthetic route to these bridged epothilone analogues has been successfully devised and implemented. Biological evaluation of the compounds against A2780 human ovarian cancer and PC3 prostate cancer cell lines suggested that the introduction of a bridge between C6-C8 reduced potency by 25-1000 fold in comparison with natural epothilone D. Tubulin assembly measurements indicate these bridged epothilone analogues to be mildly active, but without significant microtubule stabilization capacity. Molecular mechanics and DFT energy evaluations suggest the mild activity of the bridged epo-analogues may be due to internal conformational strain.     

The synthesis and fluorescent properties of analogues of the zinc(II) specific fluorophore zinquin ester

The synthesis and fluorescent properties in the absence and presence of zinc(II) of a range of 2-substituted derivatives of N-(6-methoxy-2-methyl-8-quinolyl)-4-methylbenzenesulfonamide are described. These analogues formed complexes with zinc(II) as indicated by a bathochromic shift in their UV/vis spectra. Analogues with isobutenyl and isobutyl side chains at the 2-position formed fluorescent complexes whose fluorescence was stronger than that of the 2-methyl-containing parent. These derivatives were converted, via conversion to the phenol with boron tribromide and reaction with ethyl bromoacetate, to systems with ester-containing side chains analogous to zinquin ester, a specific cellular fluorophore for zinc(II). All of these ester derivatives formed complexes with zinc(II) resulting in a bathochomic shift in their UV/vis spectra. Compounds with isobutyl, isobutenyl, and styryl side chains exhibited increased fluorescence compared to that of zinquin ester in the presence of zinc(II). The compound with the 2-isobutyl side chain was more selective in its fluorescence for zinc(II) over cadmium(II) compared to zinquin ester.     

Function Oriented Synthesis: Preparation and Initial Biological Evaluation of New A-Ring-Modified Bryologs

The synthesis and biological evaluation of the first members of a new series of designed bryostatin A-ring analogues (bryologs) are described. An advanced intermediate is produced that allows for step economical access to diverse analogs. The first of these analogues, bearing side chains of completely different polarities from alkyl to hydroxyl and carboxyl functionalities, were evaluated. All exhibit potent protein kinase C binding (54.7-2.4 nM) with affinities increasing with decreasing side chain polarity. This series of bryostatin analogues demonstrates that A-ring surrogates can indeed be used for tuning pharmacophore and ADME characteristics as needed to improve bryolog function.     

Synthesis of 8-(S)-methoxy-11-desmethyl laulimalide: a novel laulimalide analogue

A strategy is outlined which enables preparation of novel laulimalide analogues at C.8 and C.11. A representative analogue, 8-(S)-methoxy-11-desmethyl laulimalide, was synthesized via this route.     

Stereoselective total synthesis of reveromycin B and C19-epi-reveromycin B

Our studies toward the total synthesis of the reveromycin family of natural products are described herein. Our synthetic approach is efficient, stereocontrolled, and convergent and has resulted in the first synthesis of reveromycin B (4) and C19-epi-reveromycin B (55). Key steps of this successful strategy include: a modified Negishi coupling (construction of C7-C8 bond) and a Kishi-Nozaki reaction (construction of C19-C20 bond), which were employed in the attachment of the target side chains. The key building blocks for the total synthesis were thus defined as vinyl iodide 6, alkyne 7, and alkyne 8. Our synthesis illustrates the utility of the modified Negishi coupling for the construction of complex dienes, confirms the proposed stereochemistry of reveromycins and paves the way for the preparation of designed analogues for biological study.     

Preparation and properties of chiral 4-pyrrolidinopyridine (PPY) analogues with dual functional side chains

Chiral 4-pyrrolidinopyridine analogues 8-13 with two distinct functional side chains at C(2) and C(4) of the pyrrolidine ring were prepared from 4-hydroxy-l-proline. We examined desymmetrization of meso-1,3-cyclohexanediol through enantioselective acylation using these catalysts and found that introduction of a C(4)-side chain was effective for improving both the chemo- and enantioselectivity of acylation.     

Pharmacophore mapping in the laulimalide series: total synthesis of a vinylogue for a late-stage metathesis diversification strategy

An efficient synthesis of the macrocyclic core of laulimalide with a pendant vinyl group at C20 is described, allowing for late-stage introduction of various side chains through a selective and efficient cross metathesis diversification step. Representative analogues reported herein are the first to contain modifications to only the side chain dihydropyran of laulimalide and des-epoxy laulimalide. This step-economical strategy enables the rapid synthesis of new analogues using alkenes as an inexpensive, abundantly available diversification feedstock.     

Synthesis of novel analogues of 1alpha,25-dihydroxyvitamin D(3) with side chains at C-18

Novel analogues of the hormone 1alpha,25-(OH)(2)-D(3) with side chains attached to C-18 were synthesized by a versatile route in which key steps were the remote radical-induced functionalization of the 18-methyl by the C-8beta-hydroxyl group and the introduction of the side chains by Wittig reactions on a C-18-aldehyde. The triene system of the novel analogues was constructed by the convergent Lythgoe-Hoffmann la Roche approach, which involves reaction of a phosphine oxide (the ring A fragment) with a ketone (the upper fragment).     

General protocols for the synthesis of C(2)-symmetric and asymmetric 2,8-disubstituted analogues of Tröger's base via efficient bromine-lithium exchanges of 2,8-dibromo-6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine

Methods for facile synthesis of symmetric and unsymmetric functionalized analogues of Tr?ger's base were developed with use of 2,8-dibromo-6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine (2) as the starting material. C(2)-symmetric 2,8-disubstituted analogues of Tr?ger's base (4a-f) were synthesized via double bromine-lithium exchange of 2 followed by quench with electrophiles. Desymmetrization via single bromine-lithium exchange of 2, followed by quench with electrophiles, afforded asymmetric analogues of Tr?ger's base (6a-g). Further reaction of 2-bromo-8-(trimethylsilyl)-6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine (6b) produced 7a-c via single bromine-lithium exchange and subsequent quench with electrophiles.     

Regioselective synthesis of 5-trifluoromethyl-1,2,3-triazole nucleoside analogues via TBS-directed 1,3-dipolar cycloaddition reaction

Herein described was a straightforward method for the highly regioselective synthesis of 5-trifluoromethyl-1,2,3-triazole nucleoside analogues, which featured the utilization of tert-butyldimethylsilyl (TBDMS) group as the directing group in the 1,3-dipolar cycloaddition reactions. 4-tert-Butyldimethylsilyl-5-trifluoromethyl-1,2,3-triazole nucleoside analogues were generated as the only cycloaddition products in moderate yields (15-79%) via the treatment of glycosyl azides with 3,3,3-trifluoro-1-tert-butyldimethylsilylpropyne 1 in toluene at 85 °C. Removal of TBS groups in these triazole cycloadducts with tetrabutylammonium fluoride (TBAF) smoothly afforded the various 5-trifluoromethyl-1,5-disubstituted 1,2,3-triazole nucleoside analogues in good yields (40-88%).     

Improving the impact property and heat‐resistance of PLA/PC blends through coupling molecular chains at the interface

The influences of both the molecular structure and the melt viscosity differences between Poly(lactic acid) (PLA) and polycarbonate (PC) on the interpenetration of molecular chains at the interface were investigated by comparing the dynamic mechanical properties and morphologies of the as‐prepared PLA/PC solution‐casting blends with those of their corresponding annealed (180°C, 8 h) samples or PLA/PC melt blends. Additionally, two chain extenders containing epoxy groups (ADR and TGDDM) were used to improve the interfacial strength. Subsequently, the interpenetration of PLA and PC molecular chains at the interface was also surveyed. Finally, the effects of the morphology formed by after adding ADR or TGDDM on the impact property, and heat resistance were discussed. The results showed that there was no interpenetration of molecular chains at the interface in PLA/PC melt blends because of the serious hindrance of the molecular structure and the melt viscosity differences. Although the interfacial strength achieved significant increase after adding ADR or TGDDM, the increase of the interfacial strength should be caused by the connection of ADR or TGDDM molecules with PLA and PC molecules at the interface through chemical bonds rather than the entanglements of PLA and PC molecular chains because of no interpenetration of PLA and PC molecular chains at the interface. Thus, the morphology formed after adding ADR or TGDDM is still the type of complete phase separation, which may be the most suitable morphology for achieving high impact and heat resistance PLA/PC blends because these two properties strongly depend on the crystallinity of PLA phase. Copyright © 2015 John Wiley & Sons, Ltd.     

Phosphatidylcholine vesicle-mediated decomposition of hydrogen peroxide

The decomposition of hydrogen peroxide (H2O2) was examined in aqueous solution (50 mM Tris-HCl buffer, pH 7.4, containing 100 mM NaCl) at 25 degrees C in pure buffer or in the presence of either vesicles or micelles formed from various phosphatidylcholines (PCs). In the absence of PCs, more than 90% of the initially added H2O2 (1.0 mM) remained intact after incubation for 120 h. The effect of the PCs on the decomposition of H2O2 was studied by using different PCs that varied in terms of number of carbon atoms in the two acyl chains n as well as in terms of the degree of unsaturation. PCs with short hydrocarbon chains (n = 4, 6-8) were dissolved in the buffer solution in the form of nonassociated monomers or as micelles in equilibrium with monomers at a fixed PC concentration of 10 mM. The presence of these short-chain PCs slightly enhanced the H2O2 decomposition rate. Micelles formed by non-lipid detergents (sodium cholate, Triton X-100, and sodium dodecylsulfate) had a similar effect. In marked contrast, PCs with long hydrocarbon chains (n > or = 10) dispersed in buffer solution as vesicles (liposomes) significantly enhanced the rate of H2O2 decomposition, with the most effective PC being 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) at 25 degrees C. This indicates that the packing density of the PC molecules influences the reactivity, presumably through the direct interaction of the PC assemblies with H2O2 molecules. Furthermore, in the case of vesicles formed from PCs with unsaturated acyl chains (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, POPC; 1,2-dioleoyl-sn-glycero-3-phosphocholine, DOPC), carbon-carbon double bond oxidation did not occur extensively under the conditions used. This indicates that the observed effect of PCs on the decomposition of H2O2 is indeed related to the assembly structure (vesicle vs micelles vs monomers) and is clearly not related to the presence of unsaturated hydrocarbon chains. Fluorescence polarization measurements of two fluorescent probes embedded either in the acyl chain region of the vesicles (DPH, 1,6-diphenyl-1,3,5-hexatriene) or on the surface of the vesicles (TMA-DPH, 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene iodide) show that the presence of H2O2 leads to a decrease in the fluidity of the lipid-water surface and not to a change in the fluidity of the hydrophobic region of the vesicle bilayer. This indicates that the decomposition of H2O2 is triggered through interactions between H2O2 and the polar head group area of PC vesicles.     

Polycarbonate-modified epoxies. I. Studies on the reactions of epoxy resin/polycarbonate blends prior to cure

An epoxy resin based upon the diglycidyl ether of bisphenol-A was modified with poly(bisphenol A carbonate) (PC). Prior to aromatic amine cure, the possible reactions in the epoxy resin/PC blend were investigated using GPC and FTIR techniques. It was shown that at 150°C, the epoxy resin acted as a plasticizer and promoted the crystallization of PC. In addition, a transesterification between the secondary hydroxyl groups in the epoxy resin with the carbonate groups in PC occurred. This reaction resulted in degraded PC chains with phenolic hydroxyl end groups. There was no evidence of reaction of epoxide groups at 150°C in this blend. At 200°C, the secondary hydroxyl groups acted as a catalyst converting most of the aromatic–aromatic carbonates to the aromaticndash;liphatic and aliphaticndash;aliphatic carbonates through transesterification. At this elevated temperature, the secondary hydroxyl groups were regenerated by the addition reaction between the epoxide groups and the phenolic hydroxyl end groups, either from the transesterification or the hydrolysis of PC. This addition reaction combining the PC chains and epoxy chains eventually resulted in a crosslinked polymer if the extent of reaction was high. Thus, by using a melt blending process at high temperature, e.g., 200°C, a copolymer network structure of PC-modified epoxy could be formed. The fracture toughness should be increased by increasing the capability for plastic deformation due to the incorporation of PC chains into the network; results will be reported in a future study. © 1996 John Wiley & Sons, Inc.     

Synthesis of alpha-galactosyl ceramide (KRN7000) and analogues thereof via a common precursor and their preliminary biological assessment

A new practical synthesis of alpha-GalCer and of its analogues is presented, opening the chance to easily modify the sphingosine chain. The common precursor is a disaccharide, obtained by coupling tetra-O-benzyl-D-galactose with allyl 2,3-O-isopropylidene-D-lyxofuranoside. Introduction of alkyl chains via Wittig reaction (for alpha-GalCer and OCH) or via Williamson reaction (for oxa analogues) followed by standard synthetic steps allows one to efficiently obtain such compounds. The analogues are able to activate iNKT cells when presented by CD1d expressing cells.     

New polyethyleneglycol-functionalized texaphyrins: synthesis and in vitro biological studies

The synthesis of four new analogues of motexafin gadolinium (MGd), a gadolinium(III) texaphyrin complex in clinical trials for its anticancer properties, is described. These new derivatives contain either 1,2-diaminobenzene or 2,3-diaminonaphthalene subunits as the source of the imine nitrogens and bear multiple 2-[2-(2-methoxyethoxy)ethoxy]ethoxy (PEG) groups, on either meso aryl or beta-pyrrolic substituents, to increase their water solubility. All four analogues were found to be more active in vitro than the parent system MGd as judged from cell proliferation assays using the PC3 and A549 cell lines.     

Steric vs hydrogen-bonding control of atropisomerization: preparation of either diastereomer of configurationally stable allocolchicinoids

Steric vs hydrogen-bonding atropisomerization control of configurationally stable analogues of the biaryl natural product allocolchicine is described. Intramolecular hydrogen bonding between the C8 hydroxy group and the C7 oxygen functionality in (aR,7R)-diastereomer II of 2 and 4 leads to its thermodynamic stabilization relative to the opposite diastereomer (aR,7S)-I, which is manifested by the strong preference toward II under thermal equilibration conditions (>94% de). Protection of C8-OH removes the H-bonding and results in repulsive interaction between C7 and C8 functionalities, which destabilizes II. Steric tuning of the C8 protecting group in 7-12 allows for almost complete inversion of the axial configuration in 2 under thermal equilibration conditions (>96% de toward I). Previously unavailable phenolic allocolchicinoids (aR,7S)-2,I are subsequently released by deprotection.     

Reorganization of the structures,morphologies, and conformations of bulk polymers via coalescence from polymer–cyclodextrin inclusion compounds

Bulk poly(ethylene terephthalate) (PET) and bisphenol A polycarbonate (PC) samples have been produced by the coalescence of their segregated, extended chains from the narrow channels of the crystalline inclusion compounds (ICs) formed between the γ‐cyclodextrin (CD) host and PET and PC guests, which are reported for the first time. Differential scanning calorimetry, Fourier transform infrared, and X‐ray observations of PET and PC samples coalesced from their crystalline γ‐CD‐ICs suggest structures and morphologies that are different from those of samples obtained by ordinary solution and melt processing techniques. For example, as‐received PC is generally amorphous with a glass‐transition temperature (T_g) of about 150 °C; when cast from tetrahydrofuran solutions, PC is semicrystalline with a melting temperature (T_m) of about 230 °C; and after PC/γ‐CD‐IC is washed with hot water for the removal of the host γ‐CD and for the coalescence of the guest PC chains, it is semicrystalline but has an elevated T_m value of about 245 °C. PC crystals formed upon the coalescence of highly extended and segregated PC chains from the narrow channels in the γ‐CD host lattice are possibly more chain‐extended and certainly more stable than chain‐folded PC crystals grown from solution. Melting the PC crystals formed by coalescence from PC/γ‐CD‐IC produces a normal amorphous PC melt that, upon cooling, results in typical glassy PC. PET coalesced from its γ‐CD‐IC crystals, although also semicrystalline, displays a T_m value only marginally elevated from that of typical bulk or solution‐crystallized PET samples. However, after the melting of γ‐CD‐IC‐coalesced PET crystals, it is difficult to quench the resultant PET melt into the usual amorphous PET glass, characterized by a T_g value of about 80 °C. Instead, the coalesced PET melt rapidly recrystallizes during the attempted quench, and so upon reheating, it displays neither a T_g nor a crystallization exotherm but simply remelts at the as‐coalesced T_m. This behavior is unaffected by the coalesced PET sample being held above T_m for 2 h, indicating that the extended, unentangled nature of the chains in the noncrystalline regions of the coalesced PET are not easily converted into the completely disordered, randomly coiled, entangled melt. Apparently, the highly extended, unentangled characters of the PC and PET chains in their γ‐CD‐ICs are at least partially retained after they are coalesced. Initial differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared, and X‐ray observations are described here. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 992–1012, 2002     

The effect of pendant chain structure on the pyroelectric behaviour of calix(8)arene Langmuir-Blodgett films

The variation of the pyroelectric response (temperature-dependent electric polarisation) of alternate-layer acid/amine films of calix(8)arenes differs according to the structure of their pendant hydrophobic chains. t-Butyl calix(8)arenes exhibit larger pyroelectric coefficients than the t-octyl analogues. A coefficient of 15 μC m⁻² K⁻¹ has been obtained for a 13-alternate-layer sample of acid- and amine-substituted t-butyl calix(8)arene.     

Synthesis of copolyesters via interchange reactions with polypivalolactone

The synthesis of copolyesters via interchange reactions of polypivalolactone (PPVL) with bisphenol-A polycarbonate (PC) and dimethyl terephthalate (DMT) was studied. Random copolyesters with high thermal stability were obtained by heating PPVL with PC and DMT in the melt at 280 °C in the presence of tetrabutylorthotitanate (TnBT) as a catalyst. Results from SEC measurements showed that the values for M_n of these copolyesters ranged from 7,000 to 16,000. The process for preparing these copolyesters was studied in detail and based on the results of these studies, the reactions occurring during copolyester synthesis were discussed. It was found that in the early stages of the process mainly interchange reactions occurred between PPVL and PC chains, whereas the amount of terephthalate units increased only after longer reaction times.