Selective Thermal Deprotection of N-Boc Protected Amines in Continuous Flow.

Thermal N-Boc deprotection of a range of amines is readily effected in continuous flow, in the absence of an acid catalyst. While the optimum results were obtained in methanol or trifluoroethanol, deprotection can be effected in a range of solvents of different polarities. Sequential selective deprotection of N-Boc groups has been demonstrated through temperature control, as exemplified by effective removal of an aryl N-Boc group in the presence of an alkyl N-Boc group. As a proof of principle, a telescoped sequence involving selective deprotection of an aryl N-Boc group from 9h followed by benzoylation and deprotection of the remaining alkyl N-Boc group to form amide 13 proved successful.

Susceptibility of the Different Oxygen-Sensing Probes to Interferences in Respirometric Bacterial Assays with Complex Media.

Respirometric microbial assays are gaining popularity, but their uptake is limited by the availability of optimal O2 sensing materials and the challenge of validating assays with complex real samples. We conducted a comparative evaluation of four different O2-sensing probes based on Pt-porphyrin phosphors in respirometric bacterial assays performed on standard time-resolved fluorescence reader. The macromolecular MitoXpress, nanoparticle NanO2 and small molecule PtGlc4 and PtPEG4 probes were assessed with E. coli cells in five growth media: nutrient broth (NB), McConkey (MC), Rapid Coliform ChromoSelect (RCC), M-Lauryl lauryl sulfate (MLS), and Minerals-Modified Glutamate (MMG) media. Respiration profiles of the cells were recorded and analyzed, along with densitometry profiles and quenching studies of individual media components. This revealed several limiting factors and interferences impacting assay performance, which include probe quenched lifetime, instrument temporal resolution, inner filter effects (mainly by indicator dyes), probe binding to lipophilic components, and dynamic and static quenching by media components. The study allowed for the ranking of the probes based on their ruggedness, resilience to interferences and overall performance in respirometric bacterial assays. The 'shielded' probe NanO2 outperformed the established MitoXpress probe and the small molecule probes PtGlc4 and PtPEG4.

Flow photolysis of aryldiazoacetates leading to dihydrobenzofurans via intramolecular C-H insertion.

Flow photolysis of aryldiazoacetates 3-5 leads to C-H insertion to form dihydrobenzofurans 6-8 in a metal-free process, using either a medium pressure mercury lamp (250-390 nm) or LEDs (365 nm or 450 nm) with comparable synthetic outcomes. Significantly, addition of 4,4'-dimethoxybenzophenone 9 results in an increased yield and also alters the stereochemical outcome leading to preferential isolation of the trans dihydrobenzofurans 6a-8a (up to 50% yield), while the cis and trans diastereomers of 6-8 are recovered in essentially equimolar amounts in the absence of a photosensitiser (up to 26% yield).

Heterosubstituted Derivatives of PtPFPP for O2 Sensing and Cell Analysis: Structure-Activity Relationships.

Biological applications of phosphorescent probes for sensing molecular oxygen (O2) and bioimaging have gained popularity, but their choice is rather limited. We describe a family of new heterosubstituted phosphorescent bioprobes based on the Pt(II)-tetrakis(pentafluorophenyl)porphyrin (PtPFPP) dye. The probes are produced by simple click modification of its para-fluorine atoms with thiols, such as 1/2-thio-glucose, thio-poly(ethylene glycol) (PEG), or cysteamine. The probes were designed to have one cell-targeting moiety and three polar moieties forming a hydrophilic shell. Their chemical synthesis and purification were optimized to produce high reaction yields and easy scale-up. The ability to perform as cell-permeable or -impermeable probes was tuned by the polarity and molecular charge of the bioconjugate. The new PtPFPP derivatives were characterized for their spectral properties and cell-penetrating ability in the experiments with mammalian cell cultures, using a time-resolved fluorescence reader and PLIM imaging detection. Structure-activity relationships were established. Thus, the tri- and tetra-PEGylated structures showed low cell internalization allowing their use as extracellular probes, while cysteamine derivatives performed as efficient intracellular probes. No significant cytotoxicity was observed for all of the probes under the experimental conditions used.

Generation of Tosyl Azide in Continuous Flow Using an Azide Resin, and Telescoping with Diazo Transfer and Rhodium Acetate-Catalyzed O-H Insertion.

Generation of tosyl azide 12 in acetonitrile in flow under water-free conditions using an azide resin and its use in diazo transfer to a series of aryl acetates are described. Successful telescoping with a rhodium acetate-catalyzed O-H insertion has been achieved, thereby transforming the aryl acetate 8 to α-hydroxy ester 10, a key intermediate in the synthesis of clopidogrel 11, without requiring isolation or handling of either tosyl azide 12 or α-aryl-α-diazoacetate 9, or indeed having significant amounts of either present at any point. Significantly, the solution of α-diazo ester 9 was sufficiently clean to progress directly to the rhodium acetate-catalyzed step without any detrimental impact on the efficiency of the O-H insertion. In addition, the rhodium acetate-catalyzed O-H insertion process is cleaner in flow than under traditional batch conditions. Use of the azide resin offers clear safety advantages and, in addition, this approach complements earlier protocols for the generation of tosyl azide 12 in flow; this protocol is especially useful with less acidic substrates.

Exploiting Continuous Processing for Challenging Diazo Transfer and Telescoped Copper-Catalyzed Asymmetric Transformations.

Generation and use of triflyl azide in flow enables efficient synthesis of a range of α-diazocarbonyl compounds, including α-diazoketones, α-diazoamides, and an α-diazosulfonyl ester, via both Regitz-type diazo transfer and deacylative/debenzoylative diazo-transfer processes with excellent yields and offers versatility in the solvent employed, in addition to addressing the hazards associated with handling of this highly reactive sulfonyl azide. Telescoping the generation of triflyl azide and diazo-transfer process with highly enantioselective copper-mediated intramolecular aromatic addition and C-H insertion processes demonstrates that the reaction stream containing the α-diazocarbonyl compound can be obtained in sufficient purity to pass directly over the immobilized copper bis(oxazoline) catalyst without detrimentally impacting the catalyst enantioselectivity.

Exploring the synthetic potential of a marine transaminase including discrimination at a remote stereocentre.

The marine transaminase, P-ω-TA, can be employed for the transamination from 1-aminotetralins and 1-aminoindanes with differentiation of stereochemistry at both the site of reaction and at a remote stereocentre resulting in formation of ketone products with up to 93% ee. While 4-substituents are tolerated on the tetralin core, the presence of 3- or 8-substituents is not tolerated by the transaminase. In general P-ω-TA shows capacity for remote diastereoselectivity, although both the stereoselectivity and efficiency are dependent on the specific substrate structure. Optimum efficiency and selectivity are seen with 4-haloaryl-1-aminotetralins and 3-haloaryl-1-aminoindanes, which may be associated with the marine origin of this enzyme.

Synthesis of 1,2,5-oxathiazole-S-oxides by 1,3-dipolar cycloadditions of nitrile oxides to α-oxo sulfines.

Synthetic methodology for the generation of novel 1,2,5-oxathiazole-S-oxides from cycloaddition of nitrile oxide dipoles with α-oxo sulfines generated in situ via the α-sulfinyl carbenes derived from α-diazosulfoxides is described. Experimental evidence and mechanistic rationale for the unanticipated interconversion of the diastereomeric 1,2,5-oxathiazole-S-oxide cycloadducts are discussed. Notably, using rhodium acetate as a catalyst at 0 °C under traditional batch conditions led to the selective formation and isolation of the kinetic isomers, while, in contrast, using continuous flow thermolysis, optimal conditions for the synthesis and isolation of the thermodynamic isomers were established.

Synthesis of Cyclic α-Diazo-ß-keto Sulfoxides in Batch and Continuous Flow.

Diazo transfer to ß-keto sulfoxides to form stable isolable α-diazo-ß-keto sulfoxides has been achieved for the first time. Both monocyclic and benzofused ketone derived ß-keto sulfoxides were successfully explored as substrates for diazo transfer. Use of continuous flow leads to isolation of the desired compounds in enhanced yields relative to standard batch conditions, with short reaction times, increased safety profile, and potential to scale up.

Taming tosyl azide: the development of a scalable continuous diazo transfer process.

Heat and shock sensitive tosyl azide was generated and used on demand in a telescoped diazo transfer process. Small quantities of tosyl azide were accessed in a 'one pot' batch procedure using shelf stable, readily available reagents. For large scale diazo transfer reactions tosyl azide was generated and used in a telescoped flow process, to mitigate the risks associated with handling potentially explosive reagents on scale. The in situ formed tosyl azide was used to rapidly perform diazo transfer to a range of acceptors, including ß-ketoesters, ß-ketoamides, malonate esters and ß-ketosulfones. An effective in-line quench of sulfonyl azides was also developed, whereby a sacrificial acceptor molecule ensured complete consumption of any residual hazardous diazo transfer reagent. The telescoped diazo transfer process with in-line quenching was used to safely prepare over 21 g of an α-diazocarbonyl in >98% purity without any column chromatography.

Development of a continuous process for α-thio-ß-chloroacrylamide synthesis with enhanced control of a cascade transformation.

A continuous process strategy has been developed for the preparation of α-thio-ß-chloroacrylamides, a class of highly versatile synthetic intermediates. Flow platforms to generate the α-chloroamide and α-thioamide precursors were successfully adopted, progressing from the previously employed batch chemistry, and in both instances afford a readily scalable methodology. The implementation of the key α-thio-ß-chloroacrylamide casade as a continuous flow reaction on a multi-gram scale is described, while the tuneable nature of the cascade, facilitated by continuous processing, is highlighted by selective generation of established intermediates and byproducts.

Synthesis of novel 24-amino-25,26,27-trinorlanost-8-enes: cytotoxic and apoptotic potential in U937 cells.

In the present study, the synthesis of a range of novel 24-amino-25,26,27-trinorlanost-8-ene derivatives including 24-piperadino-trinorlanost-8-enes, 24-piperazino-trinorlanost-8-enes, 24-morpholino-trinorlanost-8-enes, and 24-diethylamino-trinorlanost-8-enes is reported and their cytotoxic and apoptotic potential evaluated in U937 cell lines. Excellent IC50 results for piperidine and 1-(2-hydroxyethyl)piperazine derivatives have been observed (IC50 values of 1.9 µM and 2.7 µM in U937 cells, respectively).

Taming hazardous chemistry in flow: the continuous processing of diazo and diazonium compounds.

The synthetic utilities of the diazo and diazonium groups are matched only by their reputation for explosive decomposition. Continuous processing technology offers new opportunities to make and use these versatile intermediates at a range of scales with improved safety over traditional batch processes. In this minireview, the state of the art in the continuous flow processing of reactive diazo and diazonium species is discussed.

Anti-inflammatory properties of potato glycoalkaloids in stimulated Jurkat and Raw 264.7 mouse macrophages.

AIMS: The potato glycoalkaloids, α-chaconine, α-solanine and solanidine, along with potato peel extracts were investigated for potential anti-inflammatory effects in vitro. Their potential to reduce two biomarkers of inflammation, cytokine and nitric oxide (NO) productions, were assessed in the stimulated Jurkat and macrophage models, respectively. MAIN METHODS: Cytokine and nitric oxide productions were stimulated in Jurkat and Raw 264.7 macrophages with Concanavalin A (Con A; 25 µg/ml) and lipopolysaccaride (LPS; 1 µg/ml), respectively. Selective concentrations of glycoalkaloids and potato peel extracts were added simultaneously with Con A or LPS for 24h to investigate their potential to reduce inflammatory activity. KEY FINDINGS: α-Chaconine and solanidine significantly reduced interleukin-2 (IL-2) and interleukin-8 (IL-8) productions in Con A-induced Jurkat cells. The potato peel extracts did not influence cytokine production. In LPS-stimulated Raw macrophages, α-solanine, solanidine and two potato peel extracts significantly reduced induced NO production. SIGNIFICANCE: Our findings suggest that sub-cytotoxic concentrations of potato glycoalkaloids and potato peel extracts possess anti-inflammatory effects in vitro and with further investigation may be useful in the prevention of anti-inflammatory diseases.

Design and synthesis of stable α-diazo-ß-oxo sulfoxides.

Diazo transfer adjacent to a sulfoxide moiety to provide stable, isolable α-diazo-ß-oxo sulfoxides has been achieved. Use of monocyclic and bicyclic sulfoxide precursors is critical in enabling isolation of stable derivatives, through introduction of conformational constraint, while acyclic α-diazo-ß-oxo sulfoxides are too labile to isolate and characterize.

ReactNMR and ReactIR as reaction monitoring and mechanistic elucidation tools: the NCS mediated cascade reaction of α-thioamides to α-thio-ß-chloroacrylamides.

On-flow ReactIR and (1)H NMR reaction monitoring, coupled with in situ intermediate characterization, was used to aid in the mechanistic elucidation of the N-chlorosuccinimide mediated transformation of an α-thioamide. Multiple intermediates in this reaction cascade are identified and characterized, and in particular, spectroscopic evidence for the intermediacy of the chlorosulfonium ion in the chlorination of α-thioamides is provided. Further to this, solvent effects on the outcome of the transformation are discussed. This work also demonstrates the utility of using a combination of ReactIR and flow NMR reaction monitoring (ReactNMR) for characterizing complex multicomponent reaction mixtures.

Addition-substitution reactions of 2-thio-3-chloroacrylamides with carbon, nitrogen, oxygen, sulfur and selenium nucleophiles.

Synthetically versatile conjugate addition of a range of carbon, nitrogen, oxygen, sulfur and selenium nucleophiles to the highly functionalised 2-thio-3-chloroacrylamides is described. The stereochemical and synthetic features of this transformation are discussed in detail. In most instances, the nucleophile replaces the chloro substituent with retention of stereochemistry. With the oxygen nucleophiles, a second addition can occur leading to acetals, while with the nitrogen nucleophiles, E-Z isomerism occurs in the resulting enamine derivatives. The ratio of the E/Z isomers can be rationalised on the basis of the substituent and the level of oxidation.