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PubMed2004

Divergence of carbonyl ylide reactions as a function of diazocarbonyl compound and aldehyde substituent: dioxolanes, dioxolenes, and epoxides.

The products from dirhodium(II) acetate-catalyzed reactions between diazocarbonyl compounds and a series of benzaldehydes demonstrate the extent of competition between intramolecular and intermolecular trapping of carbonyl ylide intermediates and the electronic effects that govern these transformations. With dimethyl diazomalonate, competition exists between dioxolane and epoxide formation so that with p-anisaldehyde only epoxide formation is observed and with p-nitrobenzaldehyde only 1,3-dioxolane products are formed. With methyl diazoacetoacetate, intramolecular trapping of the intermediate carbonyl ylide results in the sole production of dioxolenes. However, the vinyldiazoacetate analogue of methyl diazoacetoacetate, as its tert-butyldimethlsilyloxy derivative, only produces epoxides in its reactions with substituted benzaldehydes.

Benzaldehydes↗
PubMed2005

A study of the stereochemistry of 2-aryl-4,5-dimethyl-1,3-dioxolanes by cholesteric induction in nematic phases and circular dichroism spectroscopy.

[Chemical reaction: See text] The circular dichroism spectra and the twisting ability of a series of 2-aryl-4,5-dimethyl-1,3-dioxolanes used as dopants in nematic solvents have been related to their absolute configuration. Whereas the circular dichroism (CD) spectra are deeply affected by the substituents present in the aromatic ring, which in several cases cause sign inversion, the helical twisting power beta is only marginally influenced. The values of beta also seem not very sensitive to the rotamer population around the aromatic ring; this indicates the predominant importance of the chiral dioxolane ring in determining the cholesteric induction. These facts can be explained by the different nature of the two observables: in CD, the chirality is read by the absorbing chromophore and is deeply influenced even by small changes of this group. In cholesteric induction we are dealing instead with chiral solute-solvent interactions that determine a twist in the solvent. In light of the present and previous results, this process seems predominantly determined by short-range interactions, which are modulated by the molecular shape. From a practical point of view, a configurational correlation using CD for the present series of compounds seems problematic, while the values of beta are nicely correlated to the absolute configurations. Calculations with the surface chirality method predict well the sign and order of magnitude of beta and their limited sensitivity to the phenyl substituents and rotamer population.

Journal Article↗
PubMed2006

Photophysical properties of dioxolane-substituted pentacene derivatives dispersed in tris(quinolin-8-olato)aluminum(III).

Two novel dioxolane-substituted pentacene derivatives, namely, 6,14-bis-(triisopropylsilylethynyl)-1,3,9,11-tetraoxa-dicyclopenta[b,m]pentacene (TP-5) and 2,2,10,10-tetraethyl-6,14-bis-(triisopropylsilylethynyl)-1,3,9,11-tetraoxa-dicyclopenta[b,m]pentacene (EtTP-5), have been synthesized and spectroscopically characterized. Here, we examine the steady-state and time-resolved photoluminescence (PL) of solid-state composite films containing these pentacene derivatives dispersed in tris(quinolin-8-olato)aluminum(III) (Alq(3)). The films show narrow red emission and high absolute photoluminescence quantum yields (phi(PL) = 59% and 76% for films containing approximately 0.25 mol % TP-5 and EtTP-5, respectively). The Förster transfer radius for both guest-host systems is estimated to be approximately 33 A. The TP-5/Alq(3) thin films show a marked decrease in phi(PL) with increasing guest molecule concentrations, accompanied by dramatic changes in the PL spectra, suggesting that intermolecular interactions between pentacene molecules result in the formation of weakly radiative aggregates. In contrast, a lesser degree of fluorescence quenching is observed for EtTP-5/Alq(3) films. The measured fluorescence lifetimes of TP-5 and EtTP-5 are similar (approximately 18 ns) at low concentrations but deviate at higher concentrations as aggregation begins to play a role in the TP-5/Alq(3) films. The onset of aggregation in EtTP-5/Alq(3) films occurs at higher guest molecule concentrations (>1.00 mol %). The addition of ethyl groups on the terminal dioxolane rings leads to an increase in the intermolecular spacing in the solid, thereby reducing the tendency for pi-pi molecular stacking and aggregation.

Journal Article↗
PubMed1972

"Plasmalogen-type" cyclic acetals: formation and conformation of the 1,3-dioxanes and 1,3-dioxolanes from 1-0-cis-alk-1'-enyl-sn-glycerols.

Acid-catalyzed cyclization of 1-O-cis-alk-1'-enyl-sn-glycerol produced four structurally and geometrically isomeric long-chain cyclic acetals of glycerol. The isomers were isolated by adsorption and gas-liquid chromatography and were identified as cis-2-alkyl-5-hydroxy-1,3-dioxane (Ia), trans-2-alkyl-5-hydroxy-1,3-dioxane (IIa), cis-2-alkyl-4-hydroxymethyl-1,3-dioxolane (IIIa), and trans-2-alkyl-4-hydroxymethyl-1,3-dioxolane (IVa). The structure of each isomer was established by chemical and spectroscopic methods. Cyclization with p-toluenesulfonic acid in boiling benzene led to a thermodynamically equilibrated mixture of isomers Ia-IVa in which the cis isomers predominated. Cyclization in acetic acid was found to be kinetically controlled, and formation of the trans isomers was relatively favored. Rearrangement of the cyclic acetal isomers did not occur in acetic acid; hence, optically active five-membered ring acetals were prepared.

Acetals↗
PubMed2006

Fourier transform near-infrared vibrational circular dichroism used for on-line monitoring the epimerization of 2,2-dimethyl-1,3-dioxolane-4-methanol: A pseudo racemization reaction.

Near-infrared (near-IR) Fourier transform vibrational circular dichroism (FT-VCD) spectroscopy has been used to monitor the epimerization of (S)-(+)-2,2-dimethyl-1,3-dioxolane-4-methanol (S-DDM). The near-IR-VCD spectra display clear isolated VCD bands at the range of 4700-5050 cm(-1) resulting from the OH stretch-bend combination bands of S-DDM, which were found to decrease in intensity with increasing reaction time. The near-IR-VCD spectra of 10 reference samples obtained were subjected to partial least-squares (PLS) regression analysis, and the results were used to build predictive models for enantiomeric excess (EE) determination. Multivariate regression was carried out on three different sets of spectra, corresponding to the epimerization of S-DDM in three different solvents: methylcyclohexane, carbon tetrachloride and tetrahydrofuran. The effects of solvent in DDM epimerization are discussed in terms of the relative stabilization of the reaction intermediate of the DDM epimerization reaction. The results of these near-IR-VCD studies for the determination of EE highlights the potential of VCD for in situ real-time process monitoring of the reaction kinetics of chiral molecules in solution.

Calibration↗
PubMed1997

(+)cis-dioxolane stimulation of cytosolic calcium oscillations and phasic contractions of myometrial smooth muscle.

These studies sought to determine the intracellular mechanisms underlying muscarinic receptor stimulated phasic contractions of myometrial smooth muscle. Utilizing cytosolic calcium imaging studies with Fura-2 loaded muscle strips, along with in vitro isometric contraction studies, we have demonstrated that phasic myometrial contractions stimulated in response to (+)cis-dioxolane, a muscarinic selective acetylcholine agonist, are mediated by activation of the M3 receptor subtype resulting in stimulation of the phosphatidylinositol signaling pathway and the generation of cytosolic calcium oscillations.

Animals↗
PubMed1997

Preclinical pharmacokinetics of beta-L-dioxolane-cytidine, a novel anticancer agent, in rats.

PURPOSE: beta-L-Dioxolane-cytidine (OddC), a novel L-nucleoside analog with potent cytotoxicity in vitro, appears to be a promising candidate for anticancer therapy. In this study, a high performance liquid chromatography (HPLC) analytical method was developed and the preclinical pharmacokinetics of OddC were characterized in rats. METHODS: Adult male Sprague Dawley rats were given 10, 25, or 50 mg/kg of OddC both intravenously and orally with a 6-day washout period between doses. Each rat received one dosage level of OddC and the route of administration was assessed by a randomized crossover design. Plasma and urine concentrations were determined by HPLC. Pharmacokinetic parameters were generated by area-moment analysis. RESULTS: Following intravenous administration, the plasma concentrations of OddC declined rapidly in a biexponential manner with a terminal phase half-life of 1.65 +/- 1.12 h (mean +/- SD). Mean total, renal, and nonrenal clearances were 1.38 +/- 0.62, 0.30 +/- 0.14, and 1.08 +/- 0.59 1/h per kg. Approximately 22% of the administered dose was excreted unchanged in the urine. Thus, nonrenal clearance was the predominant route of elimination of OddC. The steady-state volume of distribution averaged 1.42 +/- 0.66 1/kg, indicating intracellular distribution of OddC. The nucleoside analog was slowly absorbed after oral administration and bioavailability varied greatly between individual rats, averaging 41 +/- 27% when calculated from urinary excretion data and 37 +/- 25% when calculated from plasma OddC concentration data. CONCLUSION: The pharmacokinetics of OddC in rats were linear over the dose range studied.

Animals↗
PubMed1984

The effect of the dioxolanes on amino acid induced excitation in the mammalian spinal cord.

The effects of the dissociative anaesthetic, etoxadrol, and the stereoisomers of dioxadrol, dexoxadrol and levoxadrol, were examined on the excitation of spinal neurones by electrophoretically administered amino acids in pentobarbitone- or urethane-anaesthetized rats, or pentobarbitone-anaesthetized cats. Both etoxadrol and the (+)isomer of dioxadrol, dexoxadrol, administered locally or systemically, exhibited a selective antagonism of N-methyl-D,L-aspartate relative to quisqualate and kainate. This selective antagonism was not observed with the (-)isomer of dioxadrol, levoxadrol. Since such a stereoselective antagonism of the excitation of spinal neurones by N-methyl-D,L-aspartate is also displayed by the dissociative anaesthetics phencyclidine and ketamine, it is suggested that a reduced efficiency at excitatory synapses utilising N-methyl-D,L-aspartate receptors contributes to that part of the pharmacological spectrum common to both arylcyclohexylamines and dioxolanes.

Animals↗
PubMed1984

Absence of mutagenicity of trioxane and dioxolane in Salmonella typhimurium.

The mutagenic activity of trioxane and dioxolane was investigated in 5 histidine-requiring strains of S. typhimurium: TA1535, TA1537, TA1538, TA98 and TA100 with and without activation by liver microsomes. They were not mutagenic under any of these conditions with any of the his- S. typhimurium tester strains (in the presence or absence of S9 mix from liver homogenate of rats induced with Aroclor 1254).

Animals↗
PubMed2005

Effects of HIV Q151M-associated multi-drug resistance mutations on the activities of (-)-beta-D-1',3'-dioxolan guanine.

The multi-drug resistance HIV-1 genotype A62V/V75I/F77L/F116Y/Q151M is associated with resistance to many nucleoside reverse transcriptase inhibitors including AZT, ddI, ddC, d4T, abacavir, and 3TC. In this study, we evaluated the antiviral activity of (-)-beta-D-1',3'-dioxolan guanine (DXG) towards mutant HIV-1 containing V75I/F77L/F116Y/Q151M (V75Icomplex) and A62V/V75I/F77L/F116Y/Q151M (A62Vcomplex) in MT-2 cells. We further investigated the mechanism of resistance by studying the incorporation of DXG 5'-triphosphate (DXG-TP) during DNA synthesis by mutant enzymes containing single mutations at Q151M or A62V, and the V75Icomplex and A62Vcomplex using pre-steady state kinetic analysis. Our studies showed that mutant virus containing V75Icomplex and A62Vcomplex were both more than 23-fold resistant to DXG, and this correlated with the 68- and 20-fold resistance changes observed in the enzymatic assay. Compared to the wild-type enzyme, DXG-TP was incorporated 39- and 21-fold less efficiently by the mutant enzyme containing V75Icomplex and A62Vcomplex, mainly due to decreases in the rate of incorporation. The A62V mutation significantly increased the rate of incorporation (k(pol)) for both dGTP (3-fold) and DXG-TP (7.9-fold), while the binding affinity of A62V HIV-1 RT for DXG-TP was decreased 14-fold. At the enzyme level, the addition of the A62V mutation to V75I/F77L/F116Y/Q151M moderately (3.4-fold) reversed the resistance to DXG-TP.

Amino Acid Substitution↗
PubMed2006

Anti-Plasmodium activity of imidazole-dioxolane compounds.

A series of imidazole-dioxolane compounds, which we hypothesize should bind to heme and thus interfere with heme catabolism in the parasite, were assayed for inhibitory activity in Plasmodium falciparum cultures and the results were compared to those obtained with Chinese hamster ovary (CHO) cells. The majority of the compounds displayed a similar ratio of inhibitory activity in the two culture systems; however, a number of the compounds tested showed promising anti-Plasmodium activity. The mechanism of action of these compounds remains unclear, however their inability to act synergistically with chloroquine suggests that, if they are inhibiting heme detoxification, they do so in a manner that does not complement the action of chloroquine.

Animals↗
PubMed2001

Modulation of proton transfer in the water wire of dioxolane-linked gramicidin channels by lipid membranes.

Proton conductance (g(H)) in single SS stereoisomers of dioxolane-linked gramicidin A (gA) channels were measured in different phospholipid bilayers at different HCl concentrations. In particular, measurements were obtained in bilayers made of 1,2-diphytanoyl 3-phosphocholine (DiPhPC) or its ethylated derivative 1,2-diphytanoyl 3-ethyl-phosphocholine (et-DiPhPC,). The difference between these phospholipids is that in et-DiPhPC one of the phosphate oxygens is covalently linked to an ethyl group and cannot be protonated. In relatively dilute acid solutions, g(H) in DiPhPC is significantly higher than in et-DiPhPC. At high acid concentrations, g(H) is the same in both diphytanoyl bilayers. Such differences in g(H) can be accounted for by surface charge effects at the membrane/solution interfaces. In the linear portion of the log g(H)-log [H] relationship, g(H) values in diphytanoyl bilayers were significantly larger (approximately 10-fold) than in neutral glyceryl monooleate (GMO) membranes. The slopes of the linear log-log relationships between g(H) and [H] in diphytanoyl and GMO bilayers are essentially the same (approximately 0.76). This slope is significantly lower than the slope of the log-log plot of proton conductivity versus proton concentration in aqueous solutions (approximately 1.00). Because the chemical composition of the membrane-channel/solution interface is strikingly different in GMO and diphytanoyl bilayers, the reduced slope in g(H)-[HCl] relationships may be a characteristic of proton transfer in the water wire inside the SS channel. Values of g(H) in diphytanoyl bilayers were also significantly larger than in membranes made of the more common biological phospholipids 1-palmitoyl 2-oleoyl phosphocholine (POPC) or 1-palmitoyl 2-oleoyl phosphoethanolamine (POPE). These differences, however, cannot be accounted for by different surface charge effects or by different internal dipole potentials. On the other hand, maximum g(H) measured in the SS channel does not depend on the composition of the bilayer and is determined essentially by the reduced mobility of protons in concentrated acid solutions. Finally, no experimental evidence was found in support of a lateral proton movement at the phospholipid/solution interface contributing to g(H) in single SS channels. Protein-lipid interactions are likely to modulate g(H) in the SS channel.

Chlorides↗
PubMed1994

A molecular dynamics study of gating in dioxolane-linked gramicidin A channels.

The gating transition of the RR and SS dioxolane ring-linked gramicidin A channels were studied with molecular dynamics simulations using a detailed atomic model. It was found that the probable reaction path, describing the transition of the ring from the exterior to the interior of the channel where it blocked the permeation pathway, involved several steps including the isomerization of the transpeptide plane dihedral angle of Val1. Reaction coordinates along this pathway were defined, and the transition rates between the stable conformers were calculated. It was found, in good accord with experimental observations, that the calculated blocking rate for the RR-linked channel was 280/s with a mean blocking time of 0.04 ms, whereas such blocking did not occur in the case of the SS-linked channel. An important observation is that the resulting lifetime for the blocked state of the RR-linked channel was in good accord with the experimental observations only when the calculations were performed in the presence of a potassium ion inside the channel.

Dioxolanes↗
PubMed1998

Attenuation of proton currents by methanol in a dioxolane-linked gramicidin A channel in different lipid bilayers.

The mobility of protons in a dioxolane-linked gramicidin A channel (D1) is comparable to the mobility of protons in aqueous solutions (Cukierman, S., E. P. Quigley, and D. S. Crumrine. 1997. Biophys. J. 73:2489-2502). Aliphatic alcohols decrease the mobility of H+ in aqueous solutions. In this study, the effects of methanol on proton conduction through D1 channels were investigated in different lipid bilayers and at different HCl concentrations. Methanol attenuated H+ currents in a voltage-independent manner. Attenuation of proton currents was also independent of H+ concentrations in solution. In phospholipid bilayers, methanol decreased the single channel conductance to protons without affecting the binding affinity of protons to bilayers. In glycerylmonooleate membranes, the attenuation of single channel proton conductances qualitatively resembled the decrease of conductivities of HCl solutions by methanol. However, in both types of lipid bilayers, single channel proton conductances through D1 channels were considerably more attenuated than the conductivities of different HCl solutions. This suggests that methanol modulates single proton currents through D1 channels. It is proposed that, on average, one methanol molecule binds to a D1 channel, and attenuates H+ conductance. The Gibbs free energy of this process (DeltaG0) is approximately 1.2 kcal/mol, which is comparable to the free energy of decrease of HCl conductivity in methanol solutions (1.6 kcal/mol). Apolar substances like urea and glucose that do not transport protons in HCl solutions and do not permeate D1 channels decreased solution conductivity and single channel conductance by a considerably larger proportion than methanol. Cs+ currents through D1 channels were considerably less (fivefold) attenuated by methanol than proton currents. It is proposed that methanol partitions inside the pore of gramicidin channels and delays the transfer of protons between water and methanol molecules, causing a significant attenuation of the single channel proton conductance. Gramicidin channels offer an interesting experimental model to study proton hopping along a single chain of water molecules interrupted by a single methanol molecule.

Biophysical Phenomena↗
PubMed2002

Stereoselective (2-naphthyl)methylation of sugar hydroxyls by the hydrogenolysis of diastereoisomeric dioxolane-type (2-naphthyl)methylene acetals.

The cis axial/equatorial OH groups of methyl alpha-L- and ethyl 1-thio-alpha-L-rhamnopyranoside, 1,6-anhydro-beta-D-mannopyranose, and 1,6-anhydro-beta-D-galactopyranose were reacted with 2-naphthaldehyde dimethyl acetal to diastereomeric dioxolane-type 2,3-O-(2-naphthyl)methylene or 3,4-O-(2-naphthyl)methylene acetals. The glycosides yielded the exo- and endo-isomers in nearly 1:1 ratio, 1,6-anhydro-beta-D-mannopyranose gave predominantly the endo-, and 1,6-anhydro-beta-D-galactopyranose exclusively endo-isomer. The acetals and some of their fully protected derivatives bearing benzyl or tert-butyldimethylsilyl groups were hydrogenolised with AlH(3) (3LiAlH(4)-AlCl(3)) or with Me(3)N.BH(3)-AlCl(3) reagents. The endo-isomers were cleaved by both reagents to give axial NAP ethers, the exo-isomers of pyranosides furnished equatorial NAP ethers. However, the exo-isomers of pyranoses gave irregular axial ethers with a > 30-fold enhancement of the reaction rates with respect to the endo-isomer.

Acetals↗
PubMed2001

Applications of the Chiralpak AD and Chiralcel OD chiral columns in the enantiomeric separation of several dioxolane compounds by supercritical fluid chromatography.

Two chiral columns based on polysaccharide derivatives (Chiralpak AD and Chiralcel OD) have been tested for the chiral separation of several dioxolane compounds, using supercritical fluid chromatography. The compounds studied included ketoconazole and some of its precursors. The effect of the different modifiers and the pressure, on the chromatographic parameters was also evaluated. In general, the alcohol modifiers provided better results than acetonitrile, and all the compounds could be separated with these two columns, but the selection of the column depends on the kind of compound.

Chromatography, Supercritical Fluid↗
PubMed2000

Chiral separation of four 1,3-dioxolane derivatives by supercritical fluid chromatography on an amylose-based column.

The chiral separation of four 1,3-dioxolane derivatives by supercritical fluid chromatography on an amylose-based column is described. The effects of mobile phase composition, temperature and pressure have been investigated. The nature of the modifier is the parameter which has the highest impact on the chiral resolution and it is more important than the polarity of the mobile phase. The organic modifier used for the best enantiomeric separation was different for each compound, because it depends strongly on the molecular structure of the compound.

Amylose↗
PubMed2003

Phase II study of troxacitabine, a novel dioxolane nucleoside analog, in patients with untreated or imatinib mesylate-resistant chronic myelogenous leukemia in blastic phase.

A phase II study of troxacitabine, a non-natural dioxolane nucleoside L-enantiomer, was conducted in patients with chronic myelogenous leukemia in blastic phase (CML-BP). Patients were untreated for BP, or treated with imatinib mesylate (IM) as sole prior therapy for BP. Troxacitabine was given as an intravenous infusion over 30 min daily for 5 days at a dose of 8.0 mg/m(2) per day. Thirty-one patients, 29 (93%) of whom had failed prior IM therapy, received 51 courses of therapy. Grade 3 or 4 toxicities included stomatitis (4%), hand-foot syndrome (18%), and skin rash (12%). Four patients (13%) responded. Troxacitabine-based combinations merit study in IM-resistant CML.

Adult↗