New Synthetic Caffeine Analogs as Modulators of the Cholinergic System.

Alzheimer's disease is a multifactorial neurodegenerative disorder. Since cholinergic deficit is a major factor in this disease, two molecular targets for its treatment are the acetylcholinesterase (AChE) and the nicotinic acetylcholine receptors (nAChRs). Given that caffeine is a natural compound that behaves as an AChE inhibitor and as a partial agonist of nAChRs, the aim of this work was to synthetize more potent bifunctional caffeine analogs that modulate these two molecular targets. To this end, a theophylline structure was connected to a pyrrolidine structure through a methylene chain of different lengths (3 to 7 carbon atoms) to give compounds 7-11 All caffeine derivatives inhibited the AChE, of which compound 11 showed the strongest effect. Electrophysiological studies showed that all compounds behave as agonists of the muscle and the neuronal α7 nAChR with greater potency than caffeine. To explore whether the different analogs could affect the nAChR conformational state, the nAChR conformational-sensitive probe crystal violet (CrV) was used. Compounds 9 and 10 conduced the nAChR to a different conformational state comparable with a control nAChR desensitized state. Finally, molecular docking experiments showed that all derivatives interacted with both the catalytic and anionic sites of AChE and with the orthosteric binding site of the nAChR. Thus, the new synthetized compounds can inhibit the AChE and activate muscle and α7 nAChRs with greater potency than caffeine, which suggests that they could be useful leaders for the development of new therapies for the treatment of different neurologic diseases. SIGNIFICANCE STATEMENT: In this work we synthetized caffeine derivatives which can inhibit acetylcholinesterase and activate both muscle and α7 nicotinic acetylcholine receptors (nAChRs) with higher potency than caffeine. These analogs can be divided into two groups: a non-desensitizing and a desensitizing nAChR group. From the nAChR non-desensitizing group, we propose compound 11 as the most interesting analog for further studies since it inhibits acetylcholinesterase with the highest potency and activates the nAChRs in the picomolar range without inducing receptor desensitization.

A double-blind, randomized, two-part, two-period crossover study to evaluate the pharmacokinetics of caffeine versus d9-caffeine in healthy subjects.

The deuterium kinetic isotope effect has been used to affect the cytochrome P450 metabolism of the deuterated versions of substances. This study compares the pharmacokinetics of caffeine, a Generally Recognized As Safe food and beverage ingredient, versus d9-caffeine, a potential caffeine alternative, and their respective metabolites at two dose levels in 20 healthy adults. A single dose of 50 mg or 250 mg of caffeine, or a molar-equivalent dose of d9-caffeine, were orally administered in solution with blood samples collected for up to 48 h post-dose. Plasma concentrations of parent and metabolites were analyzed using validated LC-MS/MS methods. Both d9-caffeine and caffeine were rapidly absorbed; however, d9-caffeine exhibited a higher (ca. 29%-43%) Cmax and 4-5-fold higher AUClast than caffeine, and lower Cmax, lower AUClast, and a 5-10-fold reduction in the relative exposure to the active metabolites of caffeine. Results were consistent in normal and rapid metabolizers, and both substances were well tolerated.

8-Alkylmercaptocaffeine derivatives: antioxidant, molecular docking, and in-vitro cytotoxicity studies.

Due to their unique pharmacological characteristics, methylxanthines are known as therapeutic agents in a fascinating range of medicinal scopes. In this report, we aimed to examine some biological effects of previously synthesized 8-alkylmercaptocaffeine derivatives. Cytotoxic and antioxidative activity of 8-alkylmercaptocaffeine derivatives were measured in malignant A549, MCF7, and C152 cell lines. Assessment of cGMP levels and caspase-3 activity were carried out using a colorimetric competitive ELISA kit. Computational approaches were employed to discover the inhibitory mechanism of synthesized compounds. Among the twelve synthesized derivatives, three compounds (C1, C5, and C7) bearing propyl, heptyl, and 3-methyl-butyl moieties showed higher and more desirable cytotoxic activity against all the studied cell lines (IC50 < 100 µM). Furthermore, C5 synergistically enhanced cisplatin-induced cytotoxicity in MCF-7 cells (CI < 1). Both C5 and C7 significantly increased caspase-3 activity and intracellular cGMP levels at specific time intervals in all studied cell lines (P < 0.05). However, these derivatives did not elevate LDH leakage (P > 0.05) and exhibited no marked ameliorating effects on oxidative damage (P > 0.05). Computational studies showed that H-bond formation between the nitrogen atom in pyrazolo[4,3-D] pyrimidine moiety with Gln817 and creating a hydrophobic cavity result in the stability of the alkyl group in the PDE5A active site. We found that synthesized 8-alkylmercaptocaffeine derivatives induced cell death in different cancer cells through the cGMP pathway. These findings will help us to get a deeper insight into the role of methylxanthines as useful alternatives to conventional cancer therapeutics.

An Organometallic Gold(I) Bis-N-Heterocyclic Carbene Complex with Multimodal Activity in Ovarian Cancer Cells.

The organometallic AuI bis-N-heterocyclic carbene complex [Au(9-methylcaffeine-8-ylidene)2 ]+ (AuTMX2 ) was previously shown to selectively and potently stabilise telomeric DNA G-quadruplex (G4) structures. This study sheds light on the molecular reactivity and mode of action of AuTMX2 in the cellular context using mass spectrometry-based methods, including shotgun proteomics in A2780 ovarian cancer cells. In contrast to other metal-based anticancer agents, this organogold compound is less prone to form coordinative bonds with biological nucleophiles and is expected to exert its drug effects mainly by non-covalent interactions. Global protein expression changes of treated cancer cells revealed a multimodal mode of action of AuTMX2 by alterations in the nucleolus, telomeres, actin stress-fibres and stress-responses, which were further supported by pharmacological assays, fluorescence microscopy and cellular accumulation experiments. Proteomic data are available via ProteomeXchange with identifier PXD020560.

Tandem mass spectrometric analysis of novel caffeine scaffold-based bifunctional compounds for Parkinson's disease.

RATIONALE: Novel bifunctional compounds composed of a caffeine scaffold attached to nicotine (C8 -6-N), 1-aminoindan (C8 -6-I), or caffeine (C8 -6-C8 ) were designed as therapeutics or diagnostics for Parkinson's disease (PD). In order to probe their pharmacological and toxicological profile, an appropriate analytical method is required. The goal of this study is to establish a tandem mass spectrometric fingerprint for the development of quantitative and qualitative methods that will aid future assessment of the in vitro and in vivo absorption, distribution, metabolism, excretion (ADME) and pharmacokinetic properties of these lead bifunctional compounds for PD. METHODS: Accurate mass measurement was performed using a hybrid quadrupole orthogonal time-of-flight mass spectrometer while multistage MS/MS and MS3 analyses were conducted using a triple quadrupole linear ion trap mass spectrometer. Both instruments are equipped with an electrospray ionization (ESI) source and were operated in the positive ion mode. The source and compound parameters were optimized for all three tested bifunctional compounds. RESULTS: The MS/MS analysis indicates that the fragmentation of C8 -6-N and C8 -6-I is driven by the dissociation of the nicotine and 1-aminoindan moieties, respectively, but not caffeine. A significant observation in the MS/MS fragmentation of C8 -6-C8 suggests that a previously reported loss of acetaldehyde during caffeine dissociation is instead a loss of CO2 . CONCLUSIONS: The collision-induced tandem mass spectrometry (CID-MS/MS) analysis of these novel bifunctional compounds revealed compound-specific diagnostic product ions and neutral losses for all three tested bifunctional compounds. The established MS/MS fingerprint will be applied to the future development of qualitative and quantitative methods.

An In Silico Study of the Antioxidant Ability for Two Caffeine Analogs Using Molecular Docking and Quantum Chemical Methods.

The antioxidant activity of molecules constitutes an important factor for the regulation of redox homeostasis and reduction of the oxidative stress. Cells affected by oxidative stress can undergo genetic alteration, causing structural changes and promoting the onset of chronic diseases, such as cancer. We have performed an in silico study to evaluate the antioxidant potential of two molecules of the zinc database: ZINC08706191 (Z91) and ZINC08992920 (Z20). Molecular docking, quantum chemical calculations (HF/6-31G**) and Pearson's correlation have been performed. Molecular docking results of Z91 and Z20 showed both the lower binding affinity (BA) and inhibition constant (Ki) values for the receptor-ligand interactions in the three tested enzymes (cytochrome P450-CP450, myeloperoxidase-MP and NADPH oxidase-NO) than the control molecules (5-fluorouracil-FLU, melatonin-MEL and dextromethorphan-DEX, for each receptor respectively). Molecular descriptors were correlated with Ki and strong correlations were observed for the CP450, MP and NO receptors. These and other results attest the significant antioxidant ability of Z91 and Z20, that may be indicated for further analyses in relation to the control of oxidative stress and as possible antioxidant agents to be used in the pharmaceutical industry.

Impact on monoclonal antibody production in murine hybridoma cell cultures of adenosine receptor antagonists and phosphodiesterase inhibitors.

The effects of different adenosine receptor antagonists and cyclic nucleotide phosphodiesterase (PDE) inhibitors on monoclonal antibody (mAb) titer and cell viability of murine hybridoma cells in culture were measured as part of our investigations to discover additives that enhance mAb production. Specific adenosine receptor antagonists and PDE inhibitors were found to enhance or decrease the titer of immunoglobulin G1 (IgG1) mAbs relative to negative controls, depending on the specific compound and cell line employed. The observed enhancements or decreases in IgG1 mAb titer appeared to be mainly due to an increase or decrease in specific productivity rates (ngmAb/cell), respectively. The different effects of the selective adenosine antagonists suggest that antagonism at the level of the adenosine A2A and A1 or the adenosine A3 receptors result in either enhancement or suppression of IgG1 mAb production by hybridoma cells. Overall, these studies have identified hitherto unknown activities of specific adenosine antagonists and PDE inhibitors which indicate they may have valuable roles as cell culture additives in industrial biomanufacturing processes designed to enhance the yields of mAbs or other recombinant proteins produced by mammalian cell culture procedures.

An Analysis of Responses to Defibrotide in the Pulmonary Vascular Bed of the Cat.

Defibrotide is a polydisperse mixture of single-stranded oligonucleotides with many pharmacologic properties and multiple actions on the vascular endothelium. Responses to defibrotide and other vasodepressor agents were evaluated in the pulmonary vascular bed of the cat under conditions of controlled pulmonary blood flow and constant left atrial pressure. Lobar arterial pressure was increased to a high steady level with the thromboxane A2 analog U-46619. Under increased-tone conditions, defibrotide caused dose-dependent decreases in lobar arterial pressure without altering systemic arterial and left atrial pressures. Responses to defibrotide were significantly attenuated after the administration of the cyclooxygenase inhibitor sodium meclofenamate. Responses to defibrotide were also significantly attenuated after the administration of both the adenosine 1 and 2 receptor antagonists 8-cyclopentyl-1,3-dimethylxanthine and 8-(3-chlorostyryl)caffeine. Responses to defibrotide were not altered after the administration of the vascular selective adenosine triphosphate-sensitive potassium channel blocker U-37883A, or after the administration of the nitric oxide synthase inhibitor L-N-(1-iminoethyl)-ornithine. These data show that defibrotide has significant vasodepressor activity in the pulmonary vascular bed of the cat. They also suggest that pulmonary vasodilator responses to defibrotide are partially dependent on both the activation of the cyclooxygenase enzyme and adenosine 1 and 2 receptor pathways and independent of the activation of adenosine triphosphate-sensitive potassium channels or the synthesis of nitric oxide in the pulmonary vascular bed of the cat.

Towards the PET radiotracer for p75 neurotrophin receptor: [(11)C]LM11A-24 shows biological activity in vitro, but unfavorable ex vivo and in vivo profile.

Mature neurotrophins as well as their pro forms are critically involved in the regulation of neuronal functions. They are signaling through three distinct types of receptors: tropomyosin receptor kinase family (TrkA/B/C), p75 neurotrophin receptor (p75(NTR)) and sortilin. Aberrant expression of p75(NTR) in the CNS is implicated in a variety of neurodegenerative diseases, including Alzheimer's disease. The goal of this work was to evaluate one of the very few reported p75(NTR) small molecule ligands as a lead compound for development of novel PET radiotracers for in vivo p75(NTR) imaging. Here we report that previously described ligand LM11A-24 shows significant inhibition of carbachol-induced persistent firing (PF) of entorhinal cortex (EC) pyramidal neurons in wild-type mice via selective interaction with p75(NTR). Based on this electrophysiological assay, the compound has very high potency with an EC50<10nM. We optimized the radiosynthesis of [(11)C]LM11A-24 as the first attempt to develop PET radioligand for in vivo imaging of p75(NTR). Despite some weak interaction with CNS tissues, the radiolabeled compound showed unfavorable in vivo profile presumably due to high hydrophilicity.

Lidocaine relaxation in isolated rat aortic rings is enhanced by endothelial removal: possible role of Kv, KATP channels and A2a receptor crosstalk.

BACKGROUND: Lidocaine is an approved local anesthetic and Class 1B antiarrhythmic with a number of ancillary properties. Our aim was to investigate lidocaine's vasoreactivity properties in intact versus denuded rat thoracic aortic rings, and the effect of inhibitors of nitric oxide (NO), prostenoids, voltage-dependent Kv and KATP channels, membrane Na+/K+ pump, and A2a and A2b receptors. METHODS: Aortic rings were harvested from adult male Sprague Dawley rats and equilibrated in an organ bath containing oxygenated, modified Krebs-Henseleit solution, pH 7.4, 37 °C. The rings were pre-contracted sub-maximally with 0.3 µM norepinephrine (NE), and the effect of increasing lidocaine concentrations was examined. Rings were tested for viability after each experiment with maximally dilating 100 µM papaverine. The drugs 4-aminopyridine (4-AP), glibenclamide, 5-hydroxydecanoate, ouabain, 8-(3-chlorostyryl) caffeine and PSB-0788 were examined. RESULTS: All drugs tested had no significant effect on basal tension. Lidocaine relaxation in intact rings was biphasic between 1 and 10 µM (Phase 1) and 10 and 1000 µM (Phase 2). Mechanical removal of the endothelium resulted in further relaxation, and at lower concentrations ring sensitivity (% relaxation per µM lidocaine) significantly increased 3.5 times compared to intact rings. The relaxing factor(s) responsible for enhancing ring relaxation did not appear to be NO- or prostacyclin-dependent, as L-NAME and indomethacin had little or no effect on intact ring relaxation. In denuded rings, lidocaine relaxation was completely abolished by Kv channel inhibition and significantly reduced by antagonists of the MitoKATP channel, and to a lesser extent the SarcKATP channel. Curiously, A2a subtype receptor antagonism significantly inhibited lidocaine relaxation above 100 µM, but not the A2b receptor. CONCLUSIONS: We show that lidocaine relaxation in rat thoracic aorta was biphasic and significantly enhanced by endothelial removal, which did not appear to be NO or prostacyclin dependent. The unknown factor(s) responsible for enhanced relaxation was significantly reduced by Kv inhibition, 5-HD inhibition, and A2a subtype inhibition indicating a potential role for crosstalk in lidocaine's vasoreactivity.

Protective effects of (E)-2-(1-hydroxyl-4-oxocyclohexyl) ethyl caffeine against hydrogen peroxide-induced injury in PC12 cells.

(E)-2-(1-hydroxyl-4-oxocyclohexyl) ethyl caffeine (HOEC), a naturally caffeic ester isolated from Incarvillea mairei, has been reported to possess anti-inflammatory activity by targeting 5-lipoxygenase. However, its other potential activities have yet to be explored. In this study, we measured antioxidant activity of HOEC using the DPPH free radical-scavenging assay. Then, we exposed rat pheochromocytoma (PC12) cells to hydrogen peroxide (H2O2)-induced damage and investigated the antioxidant activity of HOEC. Cell viability, lactate dehydrogenase (LDH) release, cellular morphology, Hoechst 33342 fluorescent staining, and apoptosis of the PC12 cells were assessed after treatment with 0.3-10 µM HOEC for 2 h and exposure to 600 µM H2O2. Additionally, glutathione reductase (GR), superoxide dismutase (SOD), lipid peroxidation malondialdehyde (MDA), and intracellular reactive oxygen species (ROS) accumulation were assayed after the PC12 cells were exposed to H2O2. To investigate mechanism, apoptosis-related protein were evaluated, including cleaved caspase 3/7, cleaved PARP, Bcl-2, Bcl-XL, and cytochrome c. The results showed that HOEC possessed potent antioxidant activity and pre-treatment with HOEC prior to H2O2 exposure significantly increased cell viability, reduced the release of LDH, ameliorated changes in cell morphology, and inhibited apoptosis. Further, HOEC did the following: reduced intracellular accumulation of ROS and MDA; rescued loss of SOD and GR activities; inhibited activated caspase-3 and caspase-7, cleaved PARP, and cytochrome c release; up-regulated the antiapoptosis-related protein Bcl-2 and Bcl-XL; and down-regulated the apoptosis-related proteins Bax and Bad. These findings suggested that HOEC may be a therapeutic agent for treating oxidative stress-derived neurodegenerative disorders.

Collision-induced dissociation studies of caffeine in positive electrospray ionisation mass spectrometry using six deuterated isotopomers and one N1-ethylated homologue.

RATIONALE: In order to deepen the understanding of electrospray ionisation collision-induced dissociation (ESI-CID) fragmentation reactions of xanthine derivatives for the identification of metabolites using low-resolution liquid chromatography/mass spectrometry (LC/MS) analysis, basic experiments using caffeine (1,3,7-trimethylxanthine) as model compound have been performed. METHODS: Six deuterium isotopomers and one N1-ethylated homologue of caffeine have been synthesized and their ESI fragmentation spectra have been obtained by using LC/MS in combination with either standard or perdeuterated eluent mixtures. RESULTS: One result of these studies is the finding that the positive charges of the ESI-CID caffeine fragments are caused by the addition of protons. Furthermore, the performed experiments allow the determination of all molecular formulae of each ESI-CID caffeine fragment. CONCLUSIONS: As basic CID reactions of caffeine have been elucidated in this work, the developed fragmentation scheme may serve as a valuable tool for the interpretation of ESI-CID fragmentation spectra of more complex xanthine derivatives and their respective metabolites.

Digitally enhanced thin layer chromatography: further development and some applications in isotopic chemistry.

Improvements to thin layer chromatography (TLC) analysis can be made easily and cheaply by the application of digital colour photography and image analysis. The combined technique, digitally enhanced TLC (DE-TLC), is applicable to the accurate quantification of analytes in mixtures, to reaction monitoring and to other typical uses of TLC. Examples are given of the application of digitally enhanced TLC to: the deuteromethylations of theophylline to [methyl-(2)H3]caffeine and of umbelliferone to [(2)H3]7-methoxycoumarin; the selection of tertiary amine bases in deuterodechlorination reactions; stoichiometry optimisation in the borodeuteride reduction of quinizarin (1,4-dihydroxyanthraquinone) and to the assessment of xanthophyll yields in Lepidium sativum seedlings grown in deuterated media.

Synthesis and biological activity of 6-selenocaffeine: potential modulator of chemotherapeutic drugs in breast cancer cells.

We report the development of a new microwave-based synthetic methodology mediated by Woollins' reagent that allowed an efficient conversion of caffeine into 6-selenocaffeine. A preliminary evaluation on the modulation of antioxidant activity upon selenation of caffeine, using the DPPH assay, indicated a mild antioxidant activity for 6-selenocaffeine, contrasting with caffeine, that exhibited no antioxidant activity under the same experimental conditions. Interestingly, whereas 6-selenocaffeine has revealed to have a low cytotoxic potential in both MCF10A and MCF-7 breast cells (24 h, up to 100 µM, MTT assay), a differential effect was observed when used in combination with the anticancer agents doxorubicin and oxaliplatin in MCF-7 breast cancer cells. The co-treatment of doxorubicin (1 µM) and 6-selenocaffeine (100 µM) resulted in a slight decrease in cellular viability when compared to doxorubicin (1 µM) alone. Conversely, the seleno-caffeine derivative at the same concentration markedly increased the viability of oxaliplatin (100 µM)-treated cells (p < 0.01). Overall, this work highlights an emerging methodology to synthesize organoselenium compounds and points out the differential roles of 6-selenocaffeine in the modulation of the cytotoxicity of anticancer agents.

Assessing the differential affinity of small molecules for noncanonical DNA structures.

The targeting of higher-order DNA structures has been thoroughly developed with G-quadruplex DNA but not with other structures like branched DNA (also known as DNA junctions). Because these alternative higher-order DNA architectures might be of high biological relevance, we implemented a high-throughput version of the FRET melting assay that enabled us to map the interactions of a candidate with four different DNA structures (duplex- and quadruplex DNA, three- and four-way junctions) in a rapid and reliable manner. We also introduce a novel index, the BONDS (branched and other noncanonical DNA selectivity) index, to conveniently quantify this differential affinity.

A thermodynamic and kinetic study of hydride transfer of a caffeine derivative.

One representative type of heterocyclic compound that can release a hydride ion is 7,8-dihydro-9-methylcaffeine (CAFH). The one-electron oxidation potential of CAFH [-0.294 (V vs Fc(+/0))] and the one-electron reduction potential of CAF(+) [-2.120 (V vs Fc(+/0))] were obtained using two different methods, CV and OSWV. Applying titration calorimetry data in thermodynamic cycles, the enthalpies of CAFH releasing a hydride ion [57.6 kcal/mol] and releasing a hydrogen atom [80.3 kcal/mol] and of its radical cation CAFH(•+) releasing a proton [33.0 kcal/mol] and releasing a hydrogen atom [38.4 kcal/mol] have been determined. Several conclusions can be drawn from the thermodynamic results: (1) CAFH is a very good single-electron donor whose single-electron oxidation potential is much less positive than that of NAD(P)H model compound BNAH [E(ox) = 0.219 V vs Fc(+/0)]. (2) The single-electron reduction potential of CAF(+) is much more negative than that of BNA(+) [E(red) = -1.419 V], which means that CAF(+) is not a good electron acceptor. Furthermore, CAFH is a very good hydride donor compared to BNAH. The results of non-steady-state kinetic studies, for the reaction of CAFH and AcrH(+)ClO(4)(-), show that the ratio of t(0.50)/t(0.05) is larger than 13.5 and the ratio of k(init)/k(pfo) is larger than 1. The pseudo-first-order rate constants obtained at different reaction stages decrease with the time, and the kinetic isotope was observed to be small at a short reaction time and slowly increases to 3.72 with the progress of the reaction. These kinetic results clearly display that the hydride transfer of CAFH to AcrH(+) in acetonitrile is not a one-step mechanism, while the thermodynamic results show that CAFH is a very good electron donor. The combination of the kinetic results with the thermodynamics analysis shows that the hydride transfer of the caffeine derivative CAFH takes place by a two-step reversible mechanism and there is an intermediate in the reaction.

Inhibition of monoamine oxidase by 8-[(phenylethyl)sulfanyl]caffeine analogues.

In a previous study we have investigated the monoamine oxidase (MAO) inhibitory properties of a series of 8-sulfanylcaffeine analogues. Among the compounds studied, 8-[(phenylethyl)sulfanyl]caffeine (IC(50) = 0.223 µM) was found to be a particularly potent inhibitor of the type B MAO isoform. In an attempt to discover potent MAO inhibitors and to further examine the structure-activity relationships (SAR) of MAO inhibition by 8-sulfanylcaffeine analogues, in the present study a series of 8-[(phenylethyl)sulfanyl]caffeine analogues were synthesized and evaluated as inhibitors of human MAO-A and -B. The results document that substitution on C3 and C4 of the phenyl ring with alkyl groups and halogens yields 8-[(phenylethyl)sulfanyl]caffeine analogues which are potent and selective MAO-B inhibitors with IC(50) values ranging from 0.017 to 0.125 µM. The MAO inhibitory properties of a series of 8-sulfinylcaffeine analogues were also examined. The results show that, compared to the corresponding 8-sulfanylcaffeine analogues, the 8-sulfinylcaffeins are weaker MAO-B inhibitors. Both the 8-sulfanylcaffeine and 8-sulfinylcaffeine analogues were found to be weak MAO-A inhibitors. This study also reports the MAO inhibition properties of selected 8-[(phenylpropyl)sulfanyl]caffeine analogues.

Inhibition of monoamine oxidase by 8-phenoxymethylcaffeine derivatives.

A recent study has reported that a series of 8-benzyloxycaffeines are potent and reversible inhibitors of both human monoamine oxidase (MAO) isoforms, MAO-A and -B. In an attempt to discover additional caffeine derivatives with potent MAO inhibitory activities, and to contribute to the known structure-activity relationships of MAO inhibition by caffeine derived compounds, the present study investigates the MAO inhibitory potencies of series of 8-phenoxymethylcaffeine and 8-[(phenylsulfanyl)methyl]caffeine derivatives. The results document that the 8-phenoxymethylcaffeine derivatives act as potent reversible inhibitors of MAO-B, with IC(50) values ranging from 0.148 to 5.78 µM. In contrast, the 8-[(phenylsulfanyl)methyl]caffeine derivatives were found to be weak inhibitors of MAO-B, with IC(50) values ranging from 4.05 to 124 µM. Neither the 8-phenoxymethylcaffeine nor the 8-[(phenylsulfanyl)methyl]caffeine derivatives exhibited high binding affinities for MAO-A. While less potent than the 8-benzyloxycaffeines as MAO-B inhibitors, this study concludes that 8-phenoxymethylcaffeines may act as useful leads for the design of MAO-B selective inhibitors. Such compounds may find application in the therapy of neurodegenerative disorders such as Parkinson's disease. Using molecular docking experiments, this study also proposes possible binding orientations of selected caffeine derivatives in the active sites of MAO-A and -B.

Shedding light on the bimolecular interactions of Cafaminol and human serum albumin: spectroscopic characterization and in-silico investigation.

Cafaminol, also known as methylcoffanolamine, is a vasoconstrictor and anticatarrhal of the methylxanthine family, which is used as a nasal decongestant. This study aimed to investigate the interaction mechanisms of human serum albumin (HSA) with Cafaminol, through several spectroscopic (fluorescence quenching, UV-visible absorption, and circular dichroism (CD) spectroscopies) and molecular modeling techniques. Stern-Volmer plots were employed to specify the fluorescence quenching mechanism, while the simulation methods were utilized to deduce the approximate binding position of Cafaminol on HSA. On the other hand, thermodynamic parameters, enthalpy and entropy changes, were determined to be, respectively, -105.88 (kJ mol-1) and -282.34 (J mol-1 K-1), using the Van't Hoff equation and analyzed later to specify the main acting forces between Cafaminol and HSA. Overall results revealed the binding of Cafaminol to the site I of HSA, as a result of an enthalpy-driven process, mainly through the van der Waals and hydrogen bonding interactions. Static quenching mechanism was found to be responsible for the fluorescence quenching of HSA in the Cafaminol presence, while the number of binding sites and apparent binding constant were measured accordingly. Docking results proposed that Cafaminol and HSA interact with a binding free energy (ΔG) of -6.5 kcal mol-1Communicated by Ramaswamy H. Sarma.

Thio- and aminocaffeine analogues as inhibitors of human monoamine oxidase.

In a recent study it was shown that 8-benzyloxycaffeine analogues act as potent reversible inhibitors of human monoamine oxidase (MAO) A and B. Although the benzyloxy side chain appears to be particularly favorable for enhancing the MAO inhibition potency of caffeine, a variety of other C8 oxy substituents of caffeine also lead to potent MAO inhibition. In an attempt to discover additional C8 substituents of caffeine that lead to potent MAO inhibition and to explore the importance of the ether oxygen for the MAO inhibition properties of C8 oxy-substituted caffeines, a series of 8-sulfanyl- and 8-aminocaffeine analogues were synthesized and their human MAO-A and -B inhibition potencies were compared to those of the 8-oxycaffeines. The results document that the sulfanylcaffeine analogues are reversible competitive MAO-B inhibitors with potencies comparable to those of the oxycaffeines. The most potent inhibitor, 8-{[(4-bromophenyl)methyl]sulfanyl}caffeine, exhibited an IC(50) value of 0.167 µM towards MAO-B. While the sulfanylcaffeine analogues also exhibit affinities for MAO-A, they display in general a high degree of MAO-B selectivity. The aminocaffeine analogues, in contrast, proved to be weak MAO inhibitors with a number of analogues exhibiting no binding to the MAO-A and -B isozymes. The results of this study are discussed with reference to possible binding orientations of selected caffeine analogues within the active site cavities of MAO-A and -B. MAO-B selective sulfanylcaffeine derived inhibitors may act as lead compounds for the design of antiparkinsonian therapies.