A small molecule sensor for fluoride based on an autoinductive, colorimetric signal amplification reaction

This article describes a small molecule reagent that is capable of detecting fluoride down to 0.12 mM (2.3 ppm) in water. The reagent reveals this level of fluoride through a novel autoinductive signal amplification reaction that produces an unambiguous colorimetric readout.     

Design of an intein that can be inhibited with a small molecule ligand

Protein splicing is a process in which an intervening sequence, the intein, catalyzes its own excision out of a larger polypeptide precursor by joining the flanking sequences, the exteins, with a native peptide bond. Inteins are almost completely promiscuous toward the nature of their extein sequences and can be inserted into virtually any host protein. The intein-mediated formation of a peptide bond between two polypeptides offers great potential to modulate protein structure and, hence, protein function on the post-translational level. In this work, we report the design of an intein that can be inhibited by the addition of a specific small molecule ligand. Our design strategy involved the generation of a trans-splicing intein, in which the intein domain is split into two-halves that are located on two separate polypeptides, each joined with the respective N- or C-terminal extein. To turn these fragments into an active intein with an incorporated "off" switch, each was fused at its newly created terminus with the F36M mutant of FKBP12, referred to as the FM domain. The F36M substitution was reported to effect a homodimerization of the usually monomeric FKBP12 protein; however, addition of the small molecule ligand, rapamycin, or synthetic derivatives thereof leads to a dissociation of the dimer. This phenomenon was exploited by first reconstituting the active intein on the basis of FM domain dimerization. Second, addition of the small molecule ligand prevented formation of the active intein complex and inhibited protein trans-splicing. This intein exhibited unexpected kinetic properties and provides a new and potentially very general means to control protein function on the post-translational level.     

Synthesis of strained cyclic peptides via an aza-Michael-acyl-transfer reaction cascade

A new method is presented to prepare strained lactams. Esterification of the C-terminus of a dipeptide with β-nitrostyrene or quinoline-type auxiliaries is followed by lactam formation by an intramolecular aza-Michael-acyl-transfer reaction cascade. Ultimately, the cyclic tetrapeptide cyclo[Phe-Tyr-Ala-Gly] has been prepared.     

Self-locked aptamer probe mediated cascade amplification strategy for highly sensitive and selective detection of protein and small molecule

In this work, a novel self-locked aptamer probe mediated cascade amplification strategy has been constructed for highly sensitive and specific detection of protein. First, the self-locked aptamer probe was designed with three functions: one was specific molecular recognition attributed to the aptamer sequence, the second was signal transduction owing to the transduction sequence, and the third was self-locking through the hybridization of the transduction sequence and part of the aptamer sequence. Then, the aptamer sequence specific recognized the target and folded into a three-way helix junction, leading to the release of the transduction sequence. Next, the 3’-end of this three-way junction acted as primer to trigger the strand displacement amplification (SDA), yielding a large amount of primers. Finally, the primers initiated the dual-exponential rolling circle amplification (DE-RCA) and generated numerous G-quadruples sequences. By inserting the fluorescent dye N-methyl mesoporphyrin IX (NMM), enhanced fluorescence signal was achieved. In this strategy, the self-locked aptamer probe was more stable to reduce the interference signals generated by the uncontrollable folding in unbounded state. Through the cascade amplification of SDA and DE-RCA, the sensitivity was further improved with a detection limit of 3.8 × 10⁻¹⁶ mol/L for protein detection. Furthermore, by changing the aptamer sequence of the probe, sensitive and selective detection of adenosine has been also achieved, suggesting that the proposed strategy has good versatility and can be widely used in sensitive and selective detection of biomolecules.     

Direct preparation of polyfunctional amino-substituted arylmagnesium reagents via an iodine-magnesium exchange reaction

The successive addition of PhMgCl and i-PrMgCl to functionalised iodoanilines allows their conversion to the corresponding amino-functionalised Grignard reagents, which react smoothly with a range of electrophiles in high yield.     

Design of a bioactive small molecule that targets the myotonic dystrophy type 1 RNA via an RNA motif-ligand database and chemical similarity searching

Myotonic dystrophy type 1 (DM1) is a triplet repeating disorder caused by expanded CTG repeats in the 3'-untranslated region of the dystrophia myotonica protein kinase (DMPK) gene. The transcribed repeats fold into an RNA hairpin with multiple copies of a 5'CUG/3'GUC motif that binds the RNA splicing regulator muscleblind-like 1 protein (MBNL1). Sequestration of MBNL1 by expanded r(CUG) repeats causes splicing defects in a subset of pre-mRNAs including the insulin receptor, the muscle-specific chloride ion channel, sarco(endo)plasmic reticulum Ca(2+) ATPase 1, and cardiac troponin T. Based on these observations, the development of small-molecule ligands that target specifically expanded DM1 repeats could be of use as therapeutics. In the present study, chemical similarity searching was employed to improve the efficacy of pentamidine and Hoechst 33258 ligands that have been shown previously to target the DM1 triplet repeat. A series of in vitro inhibitors of the RNA-protein complex were identified with low micromolar IC(50)'s, which are >20-fold more potent than the query compounds. Importantly, a bis-benzimidazole identified from the Hoechst query improves DM1-associated pre-mRNA splicing defects in cell and mouse models of DM1 (when dosed with 1 mM and 100 mg/kg, respectively). Since Hoechst 33258 was identified as a DM1 binder through analysis of an RNA motif-ligand database, these studies suggest that lead ligands targeting RNA with improved biological activity can be identified by using a synergistic approach that combines analysis of known RNA-ligand interactions with chemical similarity searching.     

Synthesis of novel tetracycles via an intramolecular Heck reaction with anti-hydride elimination

[reaction: see text] The catalytic combination of Pd(2)(dba)(3)/HP(t-Bu)(3).BF(4) and DABCO gives an unusual intramolecular Heck reaction with dihydronaphthalene substrates, yielding formal anti-hydride elimination products in good to excellent yields under mild conditions. For dibromo substrates, multiple Heck reactions are possible when an external acceptor is added to afford more highly functionalized products.     

Total synthesis of valeriananoids A, B, and C via autocatalytic diastereoselective domino Michael reaction

Natural enantiomers of unique tricyclic sesquiterpenoids, valeriananoids A-C 1-3, have been synthesized starting from bicyclo[2.2.2]octane-2,5-dione derivative 11, which was obtained by diastereoselective catalytic domino Michael reaction of oxophorone 5 with 8-phenylmenthyl acrylate 10 by LDA or silica-gel-base (NMAP-Li). The tricyclic ring was closed selectively by intramolecular 6-endo-trig mode cyclization of the ketyl radical, which was generated from keto-allylether 25 by either lithium or sodium naphthalenide.     

Construction of polycyclic spiro-indolines via an intramolecular oxidative coupling/cyclization cascade reaction process

An efficient protocol for assembling a polycyclic spiroindoline scaffold is developed, which involves an intramolecular oxidative coupling of dianions derived from indole-embodied β-ketoamides using iodine as the oxidant, and subsequent attack of oxygen anion to the resultant imine moiety. A number of tetracyclic spiroindolines are prepared with moderate to good yields.     

One-pot synthesis of benzothiazolines and napthathiazolines via cascade ortho-lithiation, cyclisation and elimination of N-arylsulfonyl lactams

ortho-Lithiation of cyclic aryl sulfonamides in the presence of phosphoryl chloride provides a very simple entry to fused polycyclic sultams (benzothiazolines and naphthathiazolines).     

Synthesis of chiral iodo-N,O-acetonide aminal scaffolds via an efficient cascade reaction of amino acid-derived epoxides

Novel amino acid-derived iodo-N,O-acetonide aminals were developed as chiral, non-epimerizable scaffolds to facilitate complex molecule synthesis. These scaffolds are readily prepared from commercially available amino acid derivatives in ?6 steps, contain an orthogonally-protected β-hydroxy amine moiety, and feature a directly reactive alkyl-iodide group for facile substitution chemistry. Further, a novel ring opening/cyclization cascade reaction was developed to prepare these compounds efficiently (59-72%) from readily available epoxide derivatives.     

Direct synthesis of fluorescent 1,3a,6a-triazapentalene derivatives via click-cyclization-aromatization cascade reaction

An efficient and versatile method was established for the preparation of 1,3a,6a-triazapentalenes. The 1,3a,6a-triazapentalene skeleton without an additional fused ring system was discovered to be a compact and highly fluorescent chromophore, which exhibited various interesting fluorescent properties such as a noteworthy correlation of luminescent wavelength with the Hammett σ(p) value and a strongly positive solvatofluorochromism.     

Iodine(V) reagents in organic synthesis. Part 1. Synthesis of polycyclic heterocycles via Dess-Martin periodinane-mediated cascade cyclization: generality, scope, and mechanism of the reaction

The scope, generality, and mechanism of the Dess-Martin periodinane-mediated cyclization reaction of unsaturated anilides discovered during the total synthesis of the CP-molecules (phomoidrides A and B) are delineated. A plethora of heterocyclic compounds are accessible by employing gamma,delta-unsaturated amides (derived from anilines and carboxylic acids), urethanes, or ureas (derived from isocyanates and allylic alcohols and amines) as substrates. Optimization of the reaction led to room-temperature conditions, while isotope labeling studies allowed a mechanistic rationale for this cascade reaction.     

Synthesis of 5-(phenylsulfanyl)-1,4-dihydropyrazine-2,3-diones via an unexpected microwave-assisted cascade reaction

An unprecedented route for the synthesis of N-1 substituted 5-(phenylsulfanyl)-1,4-dihydropyrazine-2,3-diones is disclosed starting from 5-chloro-3-(phenylsulfanyl)pyrazin-2(1H)-ones. The method comprises treatment of various 5-chloro-3-(phenylsulfanyl)pyrazin-2(1H)-ones with Na₂CO₃ in water under microwave irradiation providing the respective 5-(phenylsulfanyl)-1,4-dihydropyrazine-2,3-diones in good yields, via hydrolysis of the thioether bond and subsequent nucleophilic displacement of the chlorine by the in situ generated thiophenol. The obtained compounds are excellent precursors for the diversity oriented synthesis of pharmacologically active α,β-dicarbonyl compounds.     

Synthesis of isoquinolines and heterocycle-fused pyridines via three-component cascade reaction of aryl ketones, hydroxylamine, and alkynes

An efficient one-pot synthesis of isoquinolines and heterocycle-fused pyridines by three-component reaction of aryl ketones, hydroxylamine, and alkynes is developed. The reaction involves condensation of aryl ketones and hydroxylamine, rhodium(III)-catalyzed C-H bond activation of the in situ generated aryl ketone oximes, and cyclization with internal alkynes. This protocol enables rapid assembly of multisubstituted isoquinolines as well as γ-carbolines, furo[2,3-c]pyridines, thieno[2,3-c]pyridines, and benzofuro[2,3-c]pyridines from readily available substrates.     

Stereocontrolled construction of the dihydrothiopyrano[2,3-b]indole skeleton via an organocatalyzed asymmetric cascade sulfa-Michael-aldol reaction

We have developed an organocatalyzed asymmetric cascade sulfa-Michael-aldol reaction between 2-mercaptoindole-3-carbaldehydes and enals, which provides efficient access to the stereocontrolled construction of dihydrothiopyrano[2,3-b]indole skeletons. Under the catalysis of chiral diphenylprolinol TMS ether, the reactions ran smoothly to give the corresponding synthetically useful and pharmaceutically valuable dihydrothiopyrano[2,3-b]indoles in high yields and with 64–96% ee.     

A two-component small molecule system for activity-based detection and signal amplification: application to the visual detection of threshold levels of Pd(II)

A detection and signal amplification strategy aimed toward threshold diagnostic assays for use in resource-limited settings is described. The strategy employs two small molecule reagents that work in tandem. One reagent detects a specific analyte, while the second amplifies a colorimetric readout autocatalytically. The strategy is demonstrated using palladium(II) as a model analyte.     

Design, synthesis, and operation of small molecules that walk along tracks

The synthesis and system dynamics of a series of small-molecule walker-track conjugates, 3,4-C(n) (n = 2, 3, 4, 5, and 8), based on dynamic covalent linkages between the "feet" of the walkers and the "footholds" of the track, is described. Each walker has one acyl hydrazide and one sulfur-based foot separated by a spacer chain of "n" methylene groups, while the track consists of four footholds of alternating complementary functionalities (aldehydes and masked thiols). Upon repeatedly switching between acid and base, the walker moiety can be exchanged between the footholds on the track, primarily through a "passing-leg gait" mechanism, until a steady state, minimum energy, distribution is reached. The introduction of a kinetically controlled step in the reaction sequence (redox-mediated breaking and reforming of the disulfide linkages) can cause a directional bias in the distribution of the walker on the track. The different length walker molecules exhibit very different walking behaviors: Systems n = 2 and 3 cannot actually "walk" along the track because their stride lengths are too short to bridge the internal footholds. The walkers with longer spacers (n = 4, 5, and 8) do step up and down the track repeatedly, but a directional bias under the acid-redox conditions is only achieved for the C(4) and C(5) systems, interestingly in opposite directions (the C(8) walker has insufficient ring strain with the track). Although they are extremely rudimentary systems, the C(4) and C(5) walker-track conjugates exhibit four of the essential characteristics of linear molecular motor dynamics: processive, directional, repetitive, and progressive migration of a molecular unit up and down a molecular track.     

A rapid, one-pot, microwave-influenced synthesis of spiro-2,5-diketopiperazines via a cascade Ugi/6-exo-trig aza-Michael reaction

A rapid, cascade reaction process has been developed to access biologically validated spiro-2,5-diketopiperazines. The facile and environmentally benign method capitalizes on commercially available starting reagents for a sequential Ugi/6-exo-trig aza-Michael reaction, water as a solvent, and microwave irradiation without any extraneous additives.