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Increasing extracellular levels of serotonin (5-HT) in the brain ameliorates symptoms of depression and anxiety-related disorders, e.g., social phobias and post-traumatic stress disorder. Recent evidence from preclinical and clinical studies established the therapeutic potential of drugs inducing the release of 5-HT via the 5-HT-transporter. Nevertheless, current 5-HT releasing compounds under clinical investigation carry the risk for abuse and deleterious side effects. Here, we demonstrate that S-enantiomers of certain ring-substituted cathinones show preference for the release of 5-HT ex vivo and in vivo, and exert 5-HT-associated effects in preclinical behavioral models. Importantly, the lead cathinone compounds (1) do not induce substantial dopamine release and (2) display reduced off-target activity at vesicular monoamine transporters and 5-HT2B-receptors, indicative of low abuse-liability and low potential for adverse events. Taken together, our findings identify these agents as lead compounds that may prove useful for the treatment of disorders where elevation of 5-HT has proven beneficial.

The use of enzymes for synthetic applications is a powerful and environmentally-benign approach to increase molecular complexity. Oxidoreductases selectively introduce oxygen and hydrogen atoms into myriad substrates, catalyzing the synthesis of chemical and pharmaceutical building blocks for chemical production. However, broader application of this class of enzymes is limited by the requirements of expensive cofactors and low operational stability. Herein, we show that morpholine-based buffers, especially 3-(N-morpholino)propanesulfonic acid (MOPS), promote photoinduced flavoenzyme-catalyzed asymmetric redox transformations by regenerating the flavin cofactor viasacrificial electron donation and by increasing the operational stability of flavin-dependent oxidoreductases. The stabilization of the active forms of flavin by MOPS viaformation of the spin correlated ion pair 3[flavin−–MOPS+] ensemble reduces the formation of hydrogen peroxide, circumventing the oxygen dilemma under aerobic conditions detrimental to fragile enzymes.

Light-driven reduction of flavins, e.g.FAD or FMN, by sacrificial electron donors emerged as a convenient method to promote biocatalytic transformations. However, flavin activation has been restricted to oxygen-free conditions to prevent enzyme deactivation caused by reactive oxygen species (ROS). Herein, we show that the photoreduction of FMN by morpholines, including 3-(N-morpholino)propanesulfonic acid (MOPS), lessens the deactivation of the enoate reductase XenB from Pseudomonassp. during the stereoselective asymmetric enzymatic reduction of a model α,β-unsaturated diketone under aerobic conditions, leading to a 91% GC-yield and a stereoselectivity greater than 94%. The kinetic stability of the thermolabile XenB was increased by more than 20-fold in MOPS buffer compared to that in Tris-HCl buffer, and a pronounced positive effect on the transition midpoint temperature was observed. The reactive form of the FMN photocatalyst is stabilized by the formation of a 3[FMN−–MOPS+] ensemble, which reduces the formation of hydrogen peroxide and other ROS in the presence of oxygen. These results contribute to broaden the application of photobiocatalytic transformations using flavin-dependent reductases.

The total syntheses of all stereoisomers of notoincisol A, a recently isolated natural product with potential anti-inflammatory activity, are reported. The asymmetric synthesis was conducted employing a lipase-mediated kinetic resolution, which enables easy access to all required chiral building blocks with the aim of establishing the absolute configuration of the naturally occurring isomer. This was achieved by comparison of optical properties of the isolated compound with the synthetic derivatives obtained. Moreover, an assessment of the biological activity on PPARγ (peroxisome proliferator-activated receptor gamma) as a prominent receptor related to inflammation is reported. Only the natural isomer was found to activate the PPARγ receptor, and this phenomenon could be explained based on molecular docking studies. In addition, the pharmacological profiles of the isomers were determined using the GABAA(gamma-aminobutyric acid A) ion channel receptor as a representative target for allosteric modulation related to diverse CNS activities. These compounds were found to be weak allosteric modulators of the α1β3 and α1β2γ2 receptor subtypes.

The anxiolytic, anticonvulsant, muscle-relaxant, and sedative-hypnotic effects of benzodiazepine site ligands are mainly elicited by allosteric modulation of GABAAreceptors via their extracellular αx+/γ2– (x= 1, 2, 3, 5) interfaces. In addition, a low affinity binding site at the homologous α+/β– interfaces was reported for some benzodiazepine site ligands. Classical benzodiazepines and pyrazoloquinolinones have been used as molecular probes to develop structure–activity relationship models for benzodiazepine site activity. Considering all possible α+/β– and α+/γ– interfaces, such ligands potentially interact with as many as 36 interfaces, giving rise to undesired side effects. Understanding the binding modes at their binding sites will enable rational strategies to design ligands with desired selectivity profiles. Here, we compared benzodiazepine site ligand interactions in the high affinity α1+/γ2– site with the homologous α1+/β3– site using a successive mutational approach. We incorporated key amino acids known to contribute to high affinity benzodiazepine binding of the γ2– subunit into the β3– subunit, resulting in a quadruple mutant β3(4mut) with high affinity flumazenil (Ro 15-1788) binding properties. Intriguingly, some benzodiazepine site ligands displayed positive allosteric modulation in the tested recombinant α1β3(4mut) constructs while diazepam remained inactive. Consequently, we performed in silicomolecular docking in the wildtype receptor and the quadruple mutant. The results led to the conclusion that different benzodiazepine site ligands seem to use distinct binding modes, rather than a common binding mode. These findings provide structural hypotheses for the future optimization of both benzodiazepine site ligands, and ligands that interact with the homologous α+/β– sites.

The structural resolution of a bound ligand–receptor complex is a key asset to efficiently drive lead optimization in drug design. However, structural resolution of many drug targets still remains a challenging endeavor. In the absence of structural knowledge, scientists resort to structure–activity relationships (SARs) to promote compound development. In this study, we incorporated ligand-based knowledge to formulate a docking scoring function that evaluates binding poses for their agreement with a known SAR. We showcased this protocol by identifying the binding mode of the pyrazoloquinolinone (PQ) CGS-8216 at the benzodiazepine binding site of the GABAAreceptor. Further evaluation of the final pose by molecular dynamics and free energy simulations revealed a close proximity between the pendent phenyl ring of the PQ and γ2D56, congruent with the low potency of carboxyphenyl analogues. Ultimately, we introduced the γ2D56A mutation and in fact observed a 10-fold potency increase in the carboxyphenyl analogue, providing experimental evidence in favor of our binding hypothesis.

Leoligin is a natural lignan found in Edelweiss (Leontopodium nivalessp. alpinum). The aim of this study was to examine its influence on cholesterol efflux and to address the underlying mechanism of action. Leoligin increases apo A1- as well as 1% human plasma-mediated cholesterol efflux in THP-1 macrophages without affecting cell viability as determined by resazurin conversion. Western blot analysis revealed that the protein levels of the cholesterol efflux transporters ABCA1 and ABCG1 were upregulated, whereas the SR-B1 protein level remained unchanged upon treatment with leoligin (10 μM, 24 h). Quantitative reverse transcription PCR further uncovered that leoligin also increased ABCA1 and ABCG1 mRNA levels without affecting the half-life of the two mRNAs in the presence of actinomycin D, a transcription inhibitor. Proteome analysis revealed the modulation of protein expression fingerprint in the presence of leoligin. Taken together, these results suggest that leoligin induces cholesterol efflux in THP-1-derived macrophages by upregulating ABCA1 and ABCG1 expression. This novel activity suggests leoligin as a promising candidate for further studies addressing a possible preventive or therapeutic application in the context of atherosclerosis.

2‐Aryl/alkylamino‐3‐aryl Iand 3‐aryl/alkylamino‐2‐aryl pyridines II, as important potentially bioactive compounds, were synthesized by applying orthogonal cross‐coupling strategies. Combinations of the Suzuki–Miyaura, Liebeskind–Srogl, and Buchwald–Hartwig protocols gave access to the title compounds in a straightforward and operationally simple manner. Full control over the regioselectivity at the 2‐ and 3‐positions was achieved by using 2,3‐dichloropyridine or 3‐iodo‐2‐(methylthio)pyridine as simple, commercially available starting materials. Within this contribution, efficient and high yielding conditions were developed for the Suzuki–Miyaura cross‐coupling reaction of 2‐substituted 3‐chloropyridines, a transformation formerly underrepresented in the literature. For the synthesis of 3‐alkyl/arylamino‐2‐aryl pyridines, the stability of the methylthio group was exploited under Pd‐catalysis in the absence of a copper source. This even enabled the development of an operationally highly facile (semi)‐one‐pot protocol to access the aforementioned compound class that avoided one purification step. A series of products Iand IIwas prepared by using the developed protocols with excellent regioselectivity and good yields.

The enzymatic kinetic resolution of a broad set of β‐amino ketones was investigated by using a collection of 16 Baeyer–Villiger monooxygenases from different bacterial origins, which display various substrate specificities. Within this platform of enzymes excellent enantioselectivities (E>200) were found towards aliphatic and aromatic 4‐amino‐2‐ketones, and some enzymes even showed opposite enantioselectivity. The intermediate β‐aminoalkyl acetates underwent autohydrolysis yielding optically pure β‐amino alcohols, which are key intermediates in the synthesis of natural products and bioactive compounds of high interest for the pharmaceutical industry. Furthermore, in some cases the abnormal esters were formed.

The application of the halogen dance reaction for the synthesis of starting materials for crosscoupling reactions is reported. The obtained compounds were then successfully applied in sequential Stille and Suzuki–Miyaura crosscoupling reactions to obtain novel thiazole derivatives. © WileyVCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009

A series of 4-bromo-5-halo and 4-bromo-5-organometal-2-anilinothiazole derivatives were prepared via the halogen dance (HD) reaction. Subsequent Pd-catalyzed Stille and Suzuki-Miyaura cross-coupling reactions were performed in a sequential manner to obtain novel 4,5-diarylated-2-anilinothiazoles.

In this work the substrate profile and stereoselectivity of engineered whole cells overexpressing the Baeyer–Villiger monooxygenase from Xanthobacter sp. ZL5 with respect to biotransformations of prochiral substrates is characterized. This enzyme catalyzes the desymmetrization of cyclic ketones bearing different chemical features with stereoselectivity similar to that obtained with a related protein fromAcinetobacter as a prototype representative of the cyclohexanone monooxygenase enzyme cluster. Moreover, this biocatalyst is able to convert sterically demanding substrates previously not transformed by other enzymes with excellent enantioselectivities. These results expand the repertoire of optically pure lactones accessible by whole-cell biotransformation processes, which are useful intermediates for the synthesis of natural and bioactive products. In addition, we observed a remarkable epoxidation reaction of a non-activated C=C bond catalyzed by this monooxygenase.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

RecombinantEscherichia coli cells expressing monooxygenases of different bacterial origin were evaluated in microbial Baeyer–Villiger oxidations of racemic fused ketones. During the enzymatic oxidation process, both the “normal” lactone generated by migration of the more‐substituted carbon atom and/or the “abnormal” lactone resulting from migration of the less‐substituted carbon atom can be formed. Depending on the nature of the Baeyer–Villiger monooxygenase, either a regiodivergent biooxygenation to both lactones in high optical purities was observed or essentially racemic “normal” rearrangement product was formed. The complementary behavior of enzymes was found to correlate with our previous observation of clustering of cycloketone‐oxidizing proteins into two distinct clusters based on phylogenetic relationship and biocatalyst performance.

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Recent progress in the field of transition-metal-catalyzed cross-coupling reactions on various azole systems is summarized. Most important C–C- and C–X-bond formation methodologies (Negishi, Suzuki–Miyaura, Stille, Kumada–Corriu–Tamao, Hiyama, Sonogashira, Heck, C–H activation) are reviewed and discussed for the imidazole, oxazole, thiazole, pyrazole, isoxazole, and isothiazole system, as well as for azoles with more than two heteroatoms. This review covers the literature that appeared in the past ten years up to the end of 2005 with corresponding azoles used either as metal organyl or halide (including triflates and some other less frequently applied leaving groups); literature describing azole structures only as ligands was not included.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Oxygenation reactions of ketones to esters are referred to as Baeyer-Villiger oxidations and represent a powerful methodology in synthesis to break carbon-carbon bonds in an oxygen insertion process. Since the seminal work by Adolf Baeyer and Victor Villiger in 1899 substantial progress has been made to understand the mechanism, to predict migratory preference, and to apply this conversion in preparative chemistry. Stereoselective Baeyer-Villiger oxidation of cyclic ketones allows rapid access to chiral lactones as valuable intermediates in enantioselective synthesis. Together with organometal catalysts, biocatalysis offers a "green chemistry" methodology for this transformation. Several organisms have been identified to catalyze this reaction in the course of their metabolic pathways and an increasing number of flavin dependent monooxygenases is reported to accept a multitude of non-natural substrates. Such biocatalysts are used in synthetic chemistry either as isolated enzymes in combination with appropriate cofactor recycling systems or as living whole-cells in native or recombinant form. This review gives an overview of the most abundantly utilized enzymes and the corresponding substrate profiles together with applications in natural product and bioactive compound synthesis. The article focuses on recent developments in biocatalytic Baeyer-Villiger oxidation with promising applications in synthetic chemistry. Complementing these aspects, recent advances in characterizing the biochemistry of Baeyer-Villiger monooxygenases and novel approaches to modify and predict the catalytic performance of these enzymes, which have an impact on the potential as stereoselective catalytic entities, are discussed.

Recombinant Escherichia colioverexpressing Pseudomonassp. NCIMB 9872 cyclopentanone monooxygenase (CPMO, EC 1.14.13.16) and Acinetobactersp. NCIMB 9871 cyclohexanone monooxygenase (CHMO, EC 1.14.13.22) have been utilized in whole-cell Baeyer-Villigerbiotransformations of prochiral bicycloketones. A significant difference in substrate acceptance and stereoselectivity was observed for bicyclo[3.3.0] and bicyclo[4.3.0] substrates. A plausible mechanism of these transformations was established by means of high level DFT/B3LYP calculations suggesting an essential difference in electronic requirements for a successful enzymatic conversion, which was similarly encountered in recombinant whole-cell mediated biooxidations. Some of the lactones produced in the biocatalytic Baeyer-Villigeroxidation represent key intermediates for the synthesis of indole alkaloids.Recombinant Escherichia colioverexpressing Pseudomonassp. NCIMB 9872 cyclopentanone monooxygenase (CPMO, EC 1.14.13.16) and Acinetobactersp. NCIMB 9871 cyclohexanone monooxygenase (CHMO, EC 1.14.13.22) have been utilized in whole-cell Baeyer-Villigerbiotransformations of prochiral bicycloketones. A significant difference in substrate acceptance and stereoselectivity was observed for bicyclo[3.3.0] and bicyclo[4.3.0] substrates. A plausible mechanism of these transformations was established by means of high level DFT/B3LYP calculations suggesting an essential difference in electronic requirements for a successful enzymatic conversion, which was similarly encountered in recombinant whole-cell mediated biooxidations. Some of the lactones produced in the biocatalytic Baeyer-Villigeroxidation represent key intermediates for the synthesis of indole alkaloids.

Summary. A diastereoselective strategy for the synthesis of ?-pyrons was developed, starting from the Mg diacetonedicarboxylate complex. Initial cyclization with suitable anhydrides or acid chlorides, followed by hydrolytic decarboxylation leads to 2,6-disubstituted pyrans. Elevated pressure hydrogenation using Pd/C affords the title compounds in high diastereoselectivity. Scope and limitations of the method are outlined on selected examples.

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The microbial Baeyer–Villiger oxidation of prochiral 3,5-dimethylcyclohexanones bearing various functionalities with recombinant E. coli cells overexpressing cyclohexanone monooxygenase from Acinetobacter sp. NCIMB 9871 and cyclopentanone monooxygenase from Comamonas sp. NCIMB 9872 has been investigated. A distinct difference in substrate specificity and stereoselectivity of the two enzymes was observed, and enantiocomplementary products were obtained in some cases. The biocatalytic systems enabled access to chiral lactones as valuable intermediates for the total synthesis of various natural compounds. Substituents with varying lipophilicity and hybridization have been prepared by a diastereoselective synthetic route and subsequently bio-transformed for the investigation of conformational and electronic effects on the biooxidation,. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Summary. The synthesis of carbo- and heterocyclic aldehydes bearing an ipso-methoxy group is investigated. The synthetic sequence is based on an initial Grignard addition of an olefin to a cyclic ketone followed by methylation of the resulting tertiary alcohol. The terminal olefin serves as precursor for the aldehyde functionality. Oxidation by ozonolysis turned out to depend significantly on the distance of the donor methoxy group. The observed side reactions could be circumvented by applying a one-pot OsO 4 mediated diol formation followed by Malaprade oxidation using KIO 4. A series of carbo- and heterocyclic precursors were successfully converted to the title products.

Recombinant whole cells of Escherichia coli overexpressing Acinetobacter sp. NCIMB 9871 cyclohexanone monooxygenase (E.C. 1.14.13.22) have been utilized for the Baeyer-Villiger oxidation of prochiral perhydro-pyranones. The spatial limitatio­ns of the enzyme’s active site have been estimated by increasin­g the chain length of cis-substituents in positions 2 and 6. A diastereoselective synthetic sequence to the required substrate ketone­s has been developed utilizing high pressure hydrogenation.

We have investigated the microbial Baeyer−Villiger oxidations of pentalenones by recombinant whole cells expressing cyclohexanone monooxygenase from Acinetobacter and cyclopentanone monooxygenase from Pseudomonas. The two enzymes display a distinguishable enantiodivergent trend in the biotransformation of some prochiral substrates. A significant influence of the conformation of the fused-ring system and the polarity of the substituents on the conversion and enantioselectivity of the microbial oxidations was observed and is discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Enzyme-mediated Baeyer−Villiger oxidations offer a “green chemistry” approach for the production of chiral lactones. Several organisms have been found to catalyze this reaction in the course of their metabolic pathways. A number of flavin-dependent monooxygenases have been characterized, and acceptance of a multitude of non-natural substrates has been found. Such biocatalysts are used in synthetic chemistry either as isolated enzymes in combination with appropriate cofactor recycling systems or as living whole cells, in native or recombinant form, for the production of valuable intermediates. This review gives an overview of the most widely utilized enzymes and the corresponding substrate profiles, together with applications in natural product and bioactive compound synthesis. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Recombinant whole cells of Escherichia coli overexpressing Acinetobacter sp. NCIMB 9871 cyclohexanone monooxygenase (E.C. 1.14.13.22) have been utilized for the Baeyer-Villiger oxidation of functionalized bicyclo[3.3.0]ketones. Prochiral substrates were designed to probe the impact of polarity and spatial configuration of the functional groups on conversion and enantioselectivity. The data give additional insight into the steric requirements of the active site of the enzyme for high optical purity. The synthetic utility of the engineered E. coli strain is demonstrated and contributions to the non-natural substrate profile available so far are provided.

A straight forward synthesis of the 1,4,2benzodithiazine system bearing an ester functionality as potential inducers of systemic acquired resistance in plants was developed utilizing the ring expansion reaction of 1,3benzodithioles. The structure of the isomers obtained was established using xray diffraction. The reactivity of the products towards activated alkynes and ring contraction reactions in the presence of base is discussed.

The addition of organocuprates to the activated C*C double bond in 2H-3,3a,4,5,6,7-hexahydro-2-indenone followed by trapping of the anionic intermediate with MeI as electrophile is reported. Structural assignment of the resulting product was carried out viaits oxime using X-ray diffraction. A subsequent Beckmannrearrangement gave the desired title compound. Die Addition von Organocupraten an die aktivierte C*C Doppelbindung in 2H-3,3a,4,5,6,7-Hexahydro-2-indenon, gefolgt von einer Abfangreaktion des anionischen Zwischenprodukts mit MeI als Elektrophil, wurde untersucht. Die Strukturaufklärung des erhaltenen Produktes erfolgte mittels Röntgendiffraktion seines Oxims. Eine anschließende Beckmann-Umlagerung lieferte die gewünschte Titelverbindung.

A route to methyl thieno[2,3-d][1,2,3]thiadiazole carboxylates 3as highly potent inducers of systemic acquired resistance (SAR) is reported. The construction of the appropriately substituted thiophene precursors is elaborated. Cyclization towards the thiadiazole ring system was carried out using diazotation techniques. Eine Herstellungsmethode von Thieno[2,3-d][1,2,3]thiadiazolcarbonsäuremethylestern 3als hochwirksame Induktoren für chemisch induzierte Resistenz (SAR) wird beschrieben. Der Aufbau von entsprechend substituierten Thiophenvorstufen wird beschrieben. Der Ringschluß zum Thiadiazolringsystem erfolgte über Diazotierungstechniken.

The common synthetic method for the synthesis of fused 1,2,3thiadiazoles viadiazotization is not generally applicable to aminothiophenes. A substantially improved experimental protocol for the preparation of the title compounds as a potential inducer of systemic acquired resistance in plants is reported based on a novel cyclization mechanism viaa HuisgenWhite type rearrangement.

Links oder rechts herum?Der regioselektive Einbau von Sauerstoff in durch Baeyer‐Villiger‐Monooxygenasen (BVMOs) katalysierten Oxidationen (siehe Schema, SG: Schutzgruppe) ergibt nicht nur den erwarteten geschützten β‐Aminoalkohol, sondern kann auch genutzt werden, um β‐Aminosäuren herzustellen, wie exemplarisch für β‐Leucin gezeigt wird.

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