Theophylline and phenylephrine effects on cardiac relaxation

Synthesis, Crystal Structures, and Biological Activity Evaluation of Novel Xanthine Derivatives Containing a Pyrethroid Moiety

On the basis of the structures of natural xanthines and pyrethroid insecticides, a series of novel xanthine derivatives Ia-Is containing pyrethroid motifs were synthesized and identified by means of melting points, ¹H NMR, ¹³C NMR, and HRMS. The single crystals of compounds In and Iq were obtained, which further confirmed the structures and configurations of this type of compounds. The biological tests showed that some of them exhibited favorable insecticidal activities toward Mythimna separata Walker and Plutella xylostella L. and were superior to the natural methylxanthine compound caffeine and comparable with the insecticide tetramethrin (e.g., compound Im: LC₅₀ = 0.6162 mg/L, against P. xylostella). Among others, Im, Ib, Ij, and Ik could serve as new insecticidal leading structures for further study. Moreover, some of the compounds showed favorable fungicidal activities against a broad spectrum of plant pathogenic fungi (e.g., compound Ie: EC₅₀ = 6.0922 μg/mL, against Physalospora piricola; EC₅₀ = 9.0637 μg/mL, against Rhizoctonia cerealis), which in turn would be an exciting new finding in xanthine chemistry; Ie, Ih, and Ii could be novel fungicidal leading compounds for further investigation. The structure-activity relationships of the compounds were also analyzed and discussed in detail. The research results presented in this paper provide a useful reference and guidance for the development of new natural product-based agrochemicals.

Synthesis and evaluation of novel xanthine-acrylamides and xanthine-acrylates as insecticidal agents

BACKGROUND

The design and discovery of novel pesticidal agents according to bioactive natural products is an important aspect of agrochemical innovation. New xanthine derivatives derived from natural xanthine or methylxanthines are rich resources that possess great potential to afford new active pesticidal molecules. Herein novel xanthine derivatives were designed through a strategy of combining the methylxanthine caffeine skeleton with the acrylamide or acrylate motif of cinnamic acid derivatives.

RESULTS

A series of novel (E)-3-(1,3,7-trimethyl-2,6-dioxo-2,3,6,7-tetrahydro-1H-purin-8-yl)acrylic acid derivatives, caffeine-(E)-acrylamides and caffeine-(E)-acrylates, were synthesized and confirmed via melting points, ¹ H NMR, ¹³ C NMR and high-resolution mass spectrometry. A single crystal of compound I12 was obtained to illustrate the trans-configuration of the vinyl double bond. Preliminary insecticidal evaluations showed that some of the compounds had favorable insecticidal potentials against Mythimna separata Walker at 200 mg L^-1 . Some of the compounds exhibited excellent insecticidal activity against Plutella xylostella L. at low test concentrations, e.g. I18 and I24 with LC₅₀ values of 0.0435 and 0.0133 mg L^-1 , respectively, were found to be more potent than the insecticide control triflumuron. The structure-activity relationship (SAR) analysis is also given in detail.

CONCLUSION

Compounds I12, I18, I24 and I26 generated from the integration of natural methylxanthine (caffeine) and acrylate moieties could be novel insecticidal leading compounds for further structural optimization. The SAR analysis may bring a new inspiration to the extensive and deep investigations on new xanthine derivatives in the agrochemical area.

Xanthine scaffold: scope and potential in drug development

Medicinal plants have been the basis for discovery of various important marketed drugs. Xanthine is one such lead molecule. Xanthines in various forms (caffeine, theophylline, theobromine, etc) are abode in tea, coffee, cocoa, chocolate etc. giving them popular recognition. These compounds are best known for their diverse pharmaceutical applications as cyclic nucleotide phosphodiesterase inhibition, antagonization of adenosine receptor, anti-inflammatory, anti-microbial, anti-oxidant and anti-tumor activities. These properties incentivize to use xanthine as scaffold to develop new derivatives. Chemical synthesis contributes greater diversity in xanthine based derivatisation. With highlighting the existing challenges in chemical synthesis, the present review focuses the probable solution to fill existing lacuna. The review summarizes the available knowledge of xanthine based drugs development along with exploring new xanthine led chemical synthesis path for bringing diversification in xanthine based research. The main objective of this review is to explore the immense potential of xanthine as scaffold in drug development.

Adrenoceptor-mediated changes of excitation and contraction in ventricular heart muscle from guinea-pigs and rabbits

1. The influence of alpha-adrenoceptor stimulation on mechanical and electrophysiological parameters was investigated in ventricular preparations from guinea-pigs and rabbits. Action potential and force of contraction were measured in papillary muscles and ionic currents were measured in isolated myocytes. 2. The effects of alpha-adrenoceptor stimulation were compared with those of beta-adrenoceptor stimulation. 3. In the guinea-pig the stimulation of alpha-adrenoceptors caused a small increase in the force of contraction (less than 10% of the response to beta-adrenoceptor stimulation) which was not accompanied by any increase of the slow calcium inward current. beta-Adrenoceptor stimulation produced large increases in both force of contraction and slow inward calcium current. The noradrenaline-induced increase in the slow inward calcium current was not affected by phentolamine. 4. In the rabbit, alpha-adrenoceptor stimulation produced large increases in the force of contraction (about two thirds of those seen in response to beta-adrenoceptor stimulation). Whereas beta-adrenoceptor stimulation also produced large increases in both maximal upstroke velocity of slow-response action potentials and slow inward calcium current, there was almost no change of both parameters in response to alpha-adrenoceptor stimulation. 5. We conclude that, first, the contribution of alpha-adrenoceptors to adrenoceptor-mediated changes of force of contraction is minimal in the guinea-pig ventricle, and second, the pronounced changes of force of contraction in the rabbit ventricle in response to alpha-adrenoceptor stimulation are unrelated to changes in the slow inward calcium current.

Time parameters of contraction of inotropically responding cultured heart cells in relation to cellular cyclic AMP levels

Television video microscopy combined with photoelectric recording was used to determine the influence of a number of positive inotropic agents on the amplitude (peak height) and the course of the contraction of electrically paced myocytes in 4-day monolayer cultures derived from the heart ventricles of 1 to 2-day old rats. Cyclic AMP was determined in parallel cultures of the same cell population. Reductions in time to 90% of peak height, 90% of relaxation time, and duration of contraction caused by peak height-augmenting concentrations of isoproterenol, epinephrine, dibutyryl cyclic AMP, and 1-methyl-3-isobutylxanthine, but not of theophylline, correlated with rises in cellular cyclic AMP levels. Ouabain, a rise in extracellular CaCl2, and, in some experiments, phenylephrine in the presence of propranolol increased peak height, but did not change time to 90% of peak height, 90% of relaxation time, duration of contraction, and cyclic AMP content. These responses are compared to those observed by other authors in intact cardiac muscle and are discussed in the light of evidence linking increased myocardial cyclic AMP levels with an abbreviation of systole.

Impaired maximal rate of left ventricular relaxation in patients with coronary artery disease and left ventricular dysfunction

It has been suggested that the rate of left ventricular (LV) relaxation is related to the inotropic state, end-systolic fiber length and peak LV pressure, but little information is available regarding the rate of LV relaxation in patients with coronary artery disease (CAD) and LV dysfunction. To assess the rate of LV relaxation we obtained high-fidelity LV pressure measurements with manometer-tip catheters in 39 patients. The signal was analyzed by a digital computer to yield the maximal rate of pressure rise (pos dP/dt) and the maximal rate of pressure fall (neg dP/dt). Selective coronary arteriography and biplane LV angiography with determination of LV volumes, ejection fraction (EF) and percent abnormally contracting segments (ACS) when present, were performed in all patients. In 10 patients with normal LV function (EF greater than 0.50, no asynergy) mean neg dP/dt (2074 +/- 121 mm Hg/sec) was significantly (p less than 0.01) greater than in 29 patients with CAD and LV dysfunction (1695 +/- 66 mm Hg/sec). In nine patients with LV dysfunction and EF less than 0.35, mean neg dP/dt was reduced to 1405 +/- 107 mm Hg/sec, significantly (p less than 0.01) lower than in patients with normal LV function. Neg dP/dt correlated well with pos dP/dt (r = 0.75), with EF (r = 0.74), and with ACS (r = -0.74), and less well with LV end-systolic volume (r = 0.67). There was very poor correlation between neg dP/dt and peak LV pressure (r = 0.30). These data suggest that the rate of LV relaxation, as assessed by neg dP/dt, is impaired in patients with CAD and LV dysfunction, and the extent of impairment is related to the severity of the dysfunction as determined hemodynamically by pos dP/dt, and angiographically by EF and ACS. In these patients the maximal rate of LV relaxation is inversely related to LV end-systolic volume, and is not related to peak LV pressure.

The positive inotropic effect of phenylephrine in the presence of propranolol. Increase in time to peak force and in relaxation time without increase in c-AMP

The effects of phenylephrine on the shape of the contraction curve and on the cyclic adenosine 3',5'-monophosphate (c-AMP) content were studied in electrically driven (frequency 0.2 Hz) cat papillary muscles. All experiments were done in the presence of 1 micron propranolol in order to minimize interference from beta-adrenoceptors. 1. Phenylephrine increased the force of contraction in a concentration-dependent manner. Maximal effects (about 200% of control) occurred at 30 micron phenylephrine. 2. The positive inotropic effect (PIE) of phenylephrine was antagonized by phentolamine. Phentolamine, 5 micron, produced a parallel shift of the concentration-response curve for the PIE of phenylephrine by about two log units to the right. 3. The PIE of 30 micron phenylephrine occurred without any detectable increase in the c-AMP levels of the preparations. 4. The PIE of 30 micron phenylephrine developed about three times more slowly than the PIE of an equieffective concentration of isoprenaline. 5. The PIE of phenylephrine was accompanied by significant, concentration-dependent increases in both time to peak force and relaxation time. 6. It is concluded that the PIE of phenylephrine in the presence of propranolol is mediated mainly by a stimulation of alpha-adrenoceptors. It is unlikely to be related to an increase in c-AMP. With respect to time course and influence on the shape of the contraction curve it is qualitatively different from the effects of beta-adrenoceptor stimulation. These data are taken to support the hypothesis that the mechanical effects of alpha- and beta-adrenoceptor stimulating agents on the heart are produced by different mechanisms.

Qualitative differences between beta-adrenergic and alpha-adrenergic inotropic effects in rat heart muscle

If beta- and alpha-adrenergic inotropic effects are cyclic AMP dependent and cyclic AMP independent, respectively, they may be qualitatively different. The inotropic effects of beta-receptor stimulation (isoprenaline) and alpha-receptor stimulation (phenylephrine combined with propranolol) were characterized in isolated perfused rat hearts, rat atria and rat papillary muscles. The beta-effect reached its maximum before the alpha-effect. The alpha-effect followed a three-phasic time-course indicating both stimulatory and inhibitory components. The aortic pressure wave (perfused heart) indicated a shorter contraction phase after beta-stimulation than after alpha-stimulation. The time to peak tension (atrium, papillary muscle) was relatively shorter after isoprenaline than after alpha-stimulation, which tended to prolong it. The contraction-relaxation cycles (atrium, papillary muscle) were examined by recording the isometric tension (T), its first (T') and second (T'') deri derivatives. alpha and beta-stimulation both increased Tmax, T'max (maximal rate of tension rise), T'min (maximal rate of tension decline) and T''min (maximal rate of transition from rise to decline of tension). Isoprenaline increased T'min (papillary muscle) and T''min (atrium, papillary muscle) relatively more than did alpha-stimulation, i.e. the relaxing processes were activated relatively more by beta-stimulation. The results indicate different mechanisms for the two adrenergic inotropic effects. The relatively larger activation of relaxation by beta-stimulation is assumed to be caused by clic AMP.