AIE active piperazine appended naphthalimide-BODIPYs: photophysical properties and applications in live cell lysosomal tracking.

Piperazine appended naphthalimide-BODIPYs (NPB1-NPB4) exhibiting solvatochromism and aggregation-induced emission with a large Stokes shift (up to 146 nm) have been described. Separation of naphthalimide and BODIPY fluorophores by piperazine in these conjugates creates a donor-acceptor system and induces twisted intramolecular charge transfer, in addition to photoinduced electron transfer. The crucial role of naphthalimide, the alkyl chain length, the piperazine ring, and the solid-state packing on AIE has been extensively investigated by various studies. Superior cell permeability coupled with bio-compatibility of these conjugates offers a unique opportunity for their potential applications in live cell lysosomal tracking.

High-depth fluorescence imaging using a two-photon FRET system for mitochondrial pH in live cells and tissues.

We developed a fluorescent pH probe (1) capable of two-photon excitation and far-visible-emission based on FRET, composed of naphthalimide-piperazine-rhodamine. It exhibited a pH-dependent reversible and fast ratiometric fluorescence change in the rhodamine emission. Probe 1 was applied to image the pH perturbations of mitochondria in living cells and tissues.

Identification of phototransformation products of sildenafil (Viagra) and its N-demethylated human metabolite under simulated sunlight.

Recent publications on pharmaceutical monitoring are increasingly covering the field of illicit drugs and lately the forensic evaluation of designing illegal analogs of lifestyle drugs like the phosphodiesterase type 5 (PDE-5) inhibitors Viagra (sildenafil), Levitra (vardenafil) and Cialis (tadalafil). Recently, the presence of all three erectile dysfunction treatment drugs has been reported in wastewaters at very low concentrations. In the environment, contaminants undergo various physical or chemical processes classified into abiotic (photolysis, hydrolysis) and biotic (biodegradation) reactions. Thus, changes in the chemical structure lead to the formation of new transformation products, which may persist in the environment or be further degraded. This study describes the photolysis of sildenafil (SDF) and its human metabolite N-demethylsildenafil (DM-SDF) under simulated solar radiation (Xenon lamp). Following chromatographic separation of the irradiated samples, eight photoproducts in the SDF samples and six photoproducts for DM-SDF were detected and characterized. The combination of ultra performance liquid chromatography-electrospray ionization-quadrupole time-of-flight-mass spectrometry (UPLC-ESI-QToF-MS), liquid chromatography-atmospheric pressure chemical ionization-triple quadrupole mass spectrometry (LC-APCI-QqQ-MS) and hydrogen/deuterium-exchange experiments allowed to propose plausible chemical structures for the photoproducts, taking into account the characteristic fragmentation patterns and the accurate mass measurements. These mass spectral data provided sound evidence for the susceptibility of the piperazine ring toward photodegradation. A gradual breakdown of this heterocyclic structure gave rise to a series of products, which in part were identical for SDF and DM-SDF. The sulfonic acid, as the formal product of sulfonamide hydrolysis, was identified as key intermediate in the photolysis pathway. In both drug/metabolite molecules, phototransformation processes taking place beyond the sulfonamide group were deemed to be of minor relevance.

Effect of cyclodextrin derivation and amorphous state of complex on accelerated degradation of ziprasidone.

Inclusion complexes of ziprasidone with several ß-cyclodextrins [ß-CDs; sulfobutylether-ß-cyclodextrins (SBEßCD), hydroxypropyl-ß-cyclodextrins (HPßCD), methyl-ß-cyclodextrins (MßCD), and carboxyethyl-ß-cyclodextrins (CEßCD)] were prepared and solution stability was evaluated at elevated temperature. Solid-state stability was assessed by subjecting various CD complexes of ziprasidone, spray-dried dispersion (SDD), partially crystalline ziprasidone-SBEßCD salts, and the physical mixture of ziprasidone-SBEßCD to γ-irradiation. Degradant I was formed by oxidation of ziprasidone, which upon aldol condensation with ziprasidone formed degradant II in both solution and solid states. In the solution state, CD complexes with electron-donating side chains, such as SBEßCD and CEßCD, produced the highest oxidative degradation followed by HPßCD with 6, 3, and 4 degrees of substitution. In the solid state, crystalline drug substance and physical mixture of crystalline drug-SBEßCD showed very little to no degradation. In contrast, amorphous ßCD, MßCD, CEßCD, and SBEßCD complexes as well as the amorphous SDD exhibited greatest extent of oxidative degradation. Results suggest that electron-donating side chains of the derivatized CD interact with transition state of the oxidation reaction and catalyze drug degradation in solution, However, higher mobility in the amorphous state of CD-drug complexes promoted chemical instability of ziprasidone under accelerated conditions irrespective of the chemical nature of the side chain on CD.

Microwave-assisted synthesis and characterization of optically active poly (ester-imide)s incorporating L-alanine.

Pyromellitic dianhydride (1) was reacted with L-alanine (2) to result [N,N'-(pyromellitoyl)-bis-L-alanine diacid] (3). This compound (3) was converted to N,N'-(pyromellitoyl)-bis-L-alanine diacyl chloride (4) by reaction with thionyl chloride. The microwave-assisted polycondensation of this diacyl chloride (4) with polyethyleneglycol-diol (PEG-200) and/or three synthetic aromatic diols furnish a series of new PEIs and Co-PEIs in a laboratory microwave oven (Milestone). The resulting polymers and copolymers have inherent viscosities in the range of 0.31-0.53 dl g(-1). These polymers are optically active, thermally stable and soluble in polar aprotic solvents such as DMF, DMSO, NMP, DMAc, and sulfuric acid. All of the above polymers were fully characterized by IR spectroscopy, (1)H NMR spectroscopy, elemental analyses, specific rotation and thermal analyses. Some structural characterizations and physical properties of these optically active PEIs and Co-PEIs have been reported.

Synthesis of structurally diverse bis-peptide oligomers.

We have developed second-generation monomers 1 and 2 and improved conditions for rapidly and simultaneously closing multiple diketopiperazines on solid support. These new conditions involve either the microwave heating of a suspension of solid-supported amino-tetrafluoropropyl esters in acetic acid/triethylamine catalyst solution or continuous flow of catalyst solution through the resin, heated in a flow cell apparatus. We demonstrate that the new monomers 1 and 2 can be combined with the new conditions easily to synthesize previously inaccessible hetero and homo spiro ladder oligomers 3 and 4 and others.

Microwave-assisted solid-phase synthesis of 2,5-diketopiperazines: solvent and resin dependence.

Solid-phase synthesis of diketopiperazines (DKPs) was preformed using various combinations of resins (polystyrene, TentaGel, ArgoGel, and PEGA) and solvents (toluene, tert-butyl alcohol, water, and toluene/2-butanol (1:4, v/v). The DKPs were synthesized from solid-phase bound dipeptides via intramolecular aminolysis. Both thermal and microwave-assisted solid-phase synthesis of DKPs gave high yields of products independently of resin and organic solvent used; however, only the PEGA resin resulted in high yields of DKPs in water independent of heating method. The short reaction times, high yields, and the possibility to run reactions in water when an appropriate resin is used makes the microwave-assisted solid-phase synthesis the method of choice. The method should be suitable for solid-phase synthesis of diketopiperazine-based libraries.

Binding and photocleavage of cationic porphyrin-phenylpiperazine hybrids to DNA.

The binding properties of cationic porphyrin-phenylpiperazine hybrids to calf thymus (CT) DNA were investigated by using absorption, fluorescence and circular dichroism (CD) spectra, and the apparent affinity binding constants (K(app)) of the porphyrins for CT DNA were determined by using a competition method with ethidium bromide (EB). Intercalation of porphyrin into CT DNA occurred when two phenylpiperazines were introduced at cis position onto the periphery of cationic porphyrin. The photocleavages of pBR322 plasmid DNA by the porphyrins were consistent with the values of K(app). With [porphyrin]/[DNA base pairs] ratio increased, the binding mode tended to be outside binding, and the cleavage abilities of the porphyrins varied. In the presence of sodium azide, a quencher of 1O2, the cleavage of DNA by the porphyrin of intercalation was less inhibited.

Concerns in the development of an assay for determination of a highly conjugated adsorption-prone compound in human urine.

Concerns in pre-analytical handling of urine samples are discussed using a new KDR kinase inhibitor, 3-[5-(4-methanesulfonyl-piperazin-1-ylmethyl)-1H-indol-2-yl]-1H-quinolin-2-one (compound A), as an example of a case where high light sensitivity and low analyte recovery (high affinity for container surface) were found. The absence of these problems in plasma samples may be a result of the plasma protein content. Low recovery of the analyte from urine can be remedied by either changing the container or by using additives, such as bovine serum albumin (BSA) or non-ionic surfactant Tween-20. In the case of compound A, changing containers (polypropylene versus glass vial) or addition of BSA did bring analyte recovery up to 80%. However, the addition of 0.2% Tween-20 into urine quality controls (QCs) gave more than 95% analyte recovery, indicating effective reduction of analyte loss to the surface of containers. The urine assay using mixed-mode SPE and LC-MS/MS was not affected significantly by introducing Tween-20 into the samples. The mean SPE extraction recovery was 68.4% and matrix suppression of ionization on MS was less than 8% at all analyte concentrations. The linear range of the calibration curve was 0.5-400 ng/mL on PE Sciex API 3000 LC-MS/MS system. The assay intraday accuracy and precision were 92.1-104.8% and <4.2% (%CV), respectively. Urine QC samples, containing 0.2% Tween-20, gave excellent recovery after three cycles of freeze and thaw. Since analyte loss to its urine container surface is not unique to compound A (M. Schwartz, W. Kline, B. Matuszewski, Anal. Chim. Acta 352 (1997) 299-307; A.L. Fisher, E. DePuy, T. Shih, R. Stearns, Y. Lee, K. Gottesdiener, S. Flattery, M. De Smet, B. Keymeulen, D.G. Musson, J. Pharm. Biomed. Anal. 26 (2001) 739-752), we suggest an evaluation of the potential problem in the early stages of urine assay development to ensure reliable quantitation of analytes. The addition of Tween-20 can serve as a useful analytical tool to other analytes with similar situations.

Photochromism of an anticonvulsant, 1-diphenylmethyl-4-(6-methyl-2-pyridylmethylene-amino) piperazine, in the solid state.

The light-induced color change of 1-diphenylmethyl-4-(6-methyl-2-pyridylmethyleneamino) piperazine in the solid state was investigated. Light in the 420-700-nm visible region had no effect. Elevated temperature, dissolution, or prolonged storage in the dark at room temperatures restored the intrinsic color of the compound. IR, UV (solution), NMR, differential scanning calorimetry, and GC methods showed no detectable difference between the long wave-length UV light-exposed (yellow) and unexposed (colorless) samples of the pure compound. Long wavelength UV light exposure studies with several substituted piperazine analogs revealed a structure-activity requirement for the color conversion process. The data indicated that the transformation process from colorless (or faint yellow) to bright yellow is photochromism (phototropy) and is dependent on the intensity of the "action spectrum" in the 300-400-nm region. Studies in the solid state showed that heat-induced fading of the color followed apparent zero-order kinetics. The energy of activation, Eb, for the photochromic conversion process from the metastable (yellow) to the stable (colorless) state was estimated to be about 19 kcal/mole.