Patent Description:
In the field of medical diagnostics, in many cases, one or more analytes have to be detected in samples of a body fluid, such as blood, interstitial fluid, urine, saliva or other types of body fluids. Examples of analytes to be detected are glucose, triglycerides, lactate, cholesterol or other types of analytes typically present in these body fluids. According to the concentration and/or the presence of the analyte, an appropriate treatment may be chosen, if necessary.

Modern methods of analyte detection and measurement often rely on analyte-specific enzymes to confer specificity to the method. Frequently, redox enzymes are used, which either transfer redox equivalents to their substrate (reduction of substrate), or, more typically, withdraw redox equivalents from the substrate (oxidation of substrate). Most redox enzymes require the presence of a redox cofactor like, e.g., PQQ, NAD or FAD or the reduced forms thereof PQQH<NUM> NADH or FADH, from or to which redox equivalents are initially transferred by the enzyme. Redox equivalents withdrawn from an analyte may then be transferred, directly or indirectly, to a redoxindicator or to an electrode.

Generally, devices and methods known to the skilled person make use of test elements comprising one or more test chemistries, which, in presence of the analyte to be detected, are capable of performing one or more detectable detection reactions, such as optically or electrochemically detectable detection reactions. With regard to these test chemistries and methods related thereto, reference may be made e.g. to <NPL>, S-<NUM> to S-<NUM>, to <CIT>, and to <NPL>). For electrochemical detection of glucose, a review is provided, e.g. in <NPL>.

Redoxindicators are compounds which change their absorption upon undergoing a redox reaction (reviewed in, e.g., <NPL>; and in <NPL>). The majority of redoxindicators known in the art show a bathochromic shift, i.e. a change of spectral band position in the absorption, reflectance, transmittance, or emission spectrum to a longer wavelength, upon oxidation and there are only few examples of redox indicators showing a bathochromic shift upon reduction. Redox indicators showing a bathochromic shift upon reduction are particularly useful for colorimetric determination of an analyte.

A very well-known redoxindicator is phosphomolybdic acid (PMO). This compound, however has the disadvantage that the redox states are not very well defined (<NPL>; <NPL>). Moreover, the reduced form of PMO has also only a low extinction coefficient and PMO is not reduced directly by a reduced coenzyme and, therefore a mediator has to be used.

Alternative chromogenic redoxindicators are described in <CIT>. The drawback of the compounds described therein is the quite low extinction coefficient of the reduced form of these compounds. Furthermore, tetrazolium salts are used as redox indicators (see, e.g. <CIT>), but these compounds are not very stable and also require the use of a mediator like phenazine methosulfate to work in context with dehydrogenases (<NPL>). Phenazine methosulfate, however, is easily reduced by ascorbate, which may cause interference.

Further proposed as redoxindicators were: resazurins, in which, however, the color difference between the oxidized and the reduced form is too small for many applications; heteropoly acids (like PMO)(see, e.g. <CIT>), which, however, have a low molar extinction and an absorption maximum at a wavelength unsuited for many applications.

In <CIT>, acridine-esters are disclosed, which can be reduced by NADH to form acridan-derivatives; since acridans, in contrast to acridines, cannot be induced to undergo the hydrogen peroxide induced chemiluminescence reaction disclosed, the chemiluminescence signal was found to be inversely proportional to the NADH concentration. Moreover, the signal generated is chemiluminescence, which requires specific detection equipment and a decreasing chemiluminescence signal is hard to measure. Moreover, <CIT> discloses phenoxa-zines and phenothiazines as mediators in electrochemical determination of glucose. The compounds disclosed comprise quinoid systems, in which the π-electron system is known to be shortened upon reduction; accordingly, the compounds of <CIT> undergo a hypso-chromic shift upon reduction, which is difficult to measure.

<CIT> discloses benzothiazoles as redoxidicators which are used to measure NADH concentration in vitro.

Thus, there is a need in the art to provide redoxindicators, in particular redoxindicators avoiding the problem described above.

It is therefore an objective of the present invention to provide compounds, means and methods to comply with the aforementioned needs, avoiding at least in part the disadvantages of the prior art.

Accordingly, the present invention relates to a chemical compound or a salt or solvate thereof comprising a heterocyclic group (Het) covalently bound to a π-acceptor group (Acc), having the general structure of formula (VI)
<CHM>.

As an example, the expressions "A has B", "A comprises B" and "A includes B" may both refer to a situation in which, besides B, no other element is present in A (i.e. a situation in which a solely and exclusively consists of B) and to a situation in which, besides B, one or more further elements are present in entity A, such as element C, elements C and D or even further elements.

In an embodiment, a chemical compound comprising a structure as specified herein is derivable from a compound consisting of said formula by at most three chemical modification reactions, in a further embodiment, by at most two modification reactions, in a further embodiment, by at most one modification reaction. The term "chemical modification reaction" is known to the skilled person and relates to a chemical reaction modifying the chemical structure of a chemical compound according to the present invention, in an embodiment, without changing its characteristic structural features. Thus, in an embodiment, the term chemical modification reaction relates to a modification of a side chain of the chemical compound of the present invention. In an embodiment, modification of a side chain is alkylation, e.g. methylation or ethylation, acylation, in a further embodiment, acetylation, glycosylation, hydroxylation, hydroxyalkylation, or any combination thereof. In an embodiment, the modified chemical compound has the same or a similar activity with regard to the applications referred to herein as the parent chemical compound as described herein. In an embodiment, the compound according to the invention is modified in such a manner that it is soluble in aqueous buffered solution, in an embodiment in <NUM> sodium phosphate buffer pH <NUM> at a temperature of <NUM>. In an embodiment, said solubility is > <NUM> mmol/L, in a further embodiment > <NUM> mmol/L, in a further embodiment > <NUM> mmol/L. Substituents which increase hydrophilicity and/or solubility are well known in the art. Further examples are hydroxyl, carboxyl, sulfonic acid, phosphate and phosphonate substituents.

Further, as used in the following, the terms "preferably", "more preferably", "more preferably", "particularly", "more particularly", "specifically", "more specifically" or similar terms are used in conjunction with optional features, without restricting alternative possibilities.

As used herein, the terms "chemical compound", "salt", and "solvate" are used in their usual meaning known to the skilled chemist. If the net charge of a compound according to the present invention is positive, exemplary counter ions are trifluoromethanesulfonate (triflate), sulfate, alkyl sulfonate, tosylate, phosphate, tetrafluoroborate, hexafluorophosphate trifluoracetate, perchlorate, chloride or nitrate ions. If the net charge of a compound according to the present invention is negative, exemplary counterions are lithium, sodium, and/or potassium ions, or tetrameth-lyammonium ions. In an embodiment, the net charge of a compound according to the present invention is the net charge of the compound in aqueous solution under standard conditions of <NUM>, <NUM><NUM>Pa, and pH=<NUM>. As will be appreciated from the structural definitions provided herein, the term "tricyclic chemical compound" relates to a compound comprising a tricyclic structure as specified herein, which, in an embodiment, does not exclude that the tricyclic chemical compound comprises further cyclic structures.

The term "side chain" is understood by the skilled person and relates to an atom or chemical group attached covalently to the core part of a chemical compound as described herein, said core part also being referred to as "main chain" or "backbone". In the context of the invention, the side chain is an organic side chain as described herein below. The term "substituted" side chain relates to a side chain substituted at one or more positions, in an embodiment, at <NUM>, <NUM>, or <NUM> positions, wherein substituents may be attached at any available atom to produce a stable chemical compound. It is understood by the skilled person that the term "optionally substituted" side chain relates to an unsubstituted or to a substituted side chain.

The term "organic side chain", as used herein, relates to any, optionally substituted, side chain comprising at least one carbon atom. In an embodiment, the organic side chain is an, optionally substituted, alkyl, alkenyl, alkinyl, aryl, aralkyl, cycloalkyl, heterocycloalkyl, or heteroaryl side chain. In an embodiment, a substituted organic side chain is an organic side chain substituted with at least one substituent independently selected from -COO-, =O, -OH, -CN, halogen, -NH<NUM>, - NH(alkyl), -N(alkyl)<NUM>, -N(alkyl)<NUM>+, -NH(aryl), N(aryl)<NUM>, -NO<NUM>, -O(alkyl), -O-(CH<NUM>)n-OH, -O-(CH<NUM>)n-O(alkyl), -O(aralkyl), -O(aryl), -OPO<NUM><NUM>-, -PO<NUM><NUM>-, -OSO<NUM>- and -SO<NUM>-. In an embodiment, the alkyl, aryl, and aralkyl groups of the substituents are not further substituted by groups comprising alkyl, alkenyl, alkinyl, aryl, aralkyl, heterocycloalkyl, or heteroaryl groups. In a further embodiment, the alkyl, aryl, and aralkyl groups of the substituents are not further substituted.

The term "alkyl", as used herein, relates to a straight or branched chain, saturated hydrocarbon group, linked to the main chain by a covalent bond to at least one of its at least one carbon atoms. Further alkyl groups are straight chain alkyls, e.g., in an embodiment, methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, or branched chain alkyl groups, e.g., -CH(CH<NUM>)<NUM>, -CH(CH<NUM>CH<NUM>)<NUM>, -C(CH<NUM>)<NUM>, -C(CH<NUM>CH<NUM>)<NUM>, -CH(CH<NUM>)(CH<NUM>CH<NUM>), -CH<NUM>CH(CH<NUM>)<NUM>, -CH<NUM>CH(CH<NUM>)(CH<NUM>CH<NUM>), -CH<NUM>CH(CH<NUM>CH<NUM>)<NUM>, -CH<NUM>C(CH<NUM>)<NUM>, -CH<NUM>C(CH<NUM>CH<NUM>)<NUM>, -CH(CH3)CH(CH<NUM>)(CH<NUM>CH<NUM>), -CH<NUM>CH<NUM>CH(CH<NUM>)<NUM>, -CH<NUM>CH<NUM>CH(CH<NUM>)(CH<NUM>CH<NUM>), -CH<NUM>CH<NUM>CH(CH<NUM>CH<NUM>)<NUM>, -CH<NUM>CH<NUM>C(CH<NUM>)<NUM>, -CH<NUM>CH<NUM>C(CH<NUM>CH<NUM>)<NUM>, -CH(CH<NUM>)CH<NUM>CH(CH<NUM>)<NUM>, or -CH(CH<NUM>)CH(CH<NUM>)CH(CH<NUM>)<NUM>. Accordingly, alkyl groups include primary alkyl groups, secondary alkyl groups, and tertiary alkyl groups. Further envisaged alkyl groups are lower alkyl groups, i.e. in an embodiment, alkyl groups with at most <NUM> carbon atoms, in a further embodiment with at most <NUM> carbon atoms, in a further embodiment with at most <NUM> carbon atoms. The term "cycloalkyl" relates to a circularly closed, saturated or unsaturated hydrocarbon group, in an embodiment, with <NUM> to <NUM> carbon atoms. Further envisaged as cycloalkyls are cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl.

The term "alkenyl" side chain relates to a side chain comprising at least one C=C double bond and linked to the main chain by a covalent bond to at least one of its at least two carbon atoms. Accordingly, the term "alkinyl" side chain relates to a side chain comprising at least one C≡C triple bond linked to the main chain by a covalent bond to at least one of its at least two carbon atoms.

The term "cycloalkenyl" relates to a circularly closed hydrocarbon group, in an embodiment, with <NUM> to <NUM> carbon atoms, comprising at least one C=C double bond and linked to the main chain by a covalent bond to at least one of its at least two carbon atoms. The term "cycloalkinyl" relates to a circularly closed hydrocarbon group, in an embodiment, with <NUM> to <NUM> carbon atoms, comprising at least one C≡C triple bond and linked to the main chain by a covalent bond to at least one of its at least two carbon atoms.

As used herein, the term "alkoxy" side chain relates to an -O-alkyl side chain, in an embodiment, having the indicated number of carbon atoms. In an embodiment, the alkoxy side chain is -O-methyl, -O-ethyl, -O-propyl, -O-isopropyl, -O-butyl, -O-sec-butyl, -O-tert-butyl, -O-pentyl, -O-isopentyl, -O-neopentyl, -O-hexyl, -O- isohexyl, or -O-neohexyl. In an embodiment, the alkoxy side chain is -O-methyl or -O-ethyl.

The term "aryl", as used herein, relates to an aromatic ring or ring system having <NUM> to <NUM> carbon atoms, in an embodiment, comprising one, two, or three aromatic rings. Further evisaged aryl side chains are phenyl, naphthyl, anthracenyl, and phenanthrenyl. The term "ring", in the context of the chemical compounds of the present invention, is understood by the skilled person; accordingly, the term "ring system" relates to a chemical structure comprising at least two rings sharing at least one covalent bond. Thus, in an embodiment, "aryl" also includes aromatic ring systems fused with a cycloalkyl and/or a heterocycloalkyl ring.

As used herein, the term "aralkyl" relates to an alkyl side chain, wherein at least one hydrogen is replaced by an aryl side chain. In an embodiment, aralkyl is benzyl or phenethyl.

The term "heterocycloalkyl", as used herein, relates to a saturated or partially unsaturated ring or ring system having <NUM> to <NUM> ring atoms, in an embodiment, <NUM> to <NUM> ring atoms, wherein at least one ring atom is a heteroatom selected from the group consisting of N, O, and S, said ring or ring system being linked to the main chain by a covalent bond to a C or N atom of said ring or ring system. In an embodiment, heterocycloalkyl is azepinyl, dihydrofuryl, dihydropyranyl, imidazol-idinyl, imidazolinyl, isothiazolidinyl, isoxazolidinyl, morpholinyl, oxazolidinyl, piperazinyl, piperidinyl, pyrazolidinyl, pyrrolidinyl, tetrahydrofuryl, tetrahydropyranyl, thiadiazolylidinyl, thiazolidinyl, or thiomorpholinyl.

As used herein, the term "heteroaryl" relates to an aromatic ring or ring system having <NUM> to <NUM> ring atoms, in an embodiment, <NUM> to <NUM> ring atoms, wherein at least one ring atom is a heteroatom selected from the group consisting of N, O, and S, said ring or ring system being linked to the main chain by a covalent bond to a C or N atom of said ring or ring system. In an embodiment, up to <NUM>, in a further embodiment, up to <NUM>, in a further embodiment, up to <NUM> ring atoms per ring are heteroatoms independently selected from the group of heteroatoms consisting of N, O, and S. In an embodiment, heteroaryl is pyridinyl, pyridazinyl, pyrazinyl, quinaoxalyl, indolizinyl, ben-zo[b]thienyl, quinazolinyl, purinyl, indolyl, quinolinyl, pyrimidinyl, pyrrolyl, pyrazolyl, oxazolyl, thiazolyl, thienyl, isoxazolyl, oxathiadiazolyl, isothiazolyl, tetrazolyl, imidazolyl, triazolyl, furanyl, benzofuryl, or indolyl.

Generally, reduction as used in the context with the compounds of the present invention relates to acquisition of two electrons by the ring system according to the following general scheme, shown for a compound not covered by the present invention:
<CHM>
oxidized form reduction
<CHM>
oxidation
<CHM>
reduced form.

In the above figures, Acc represents a π-acceptor group as detailed above.

Accordingly, in the compounds of the present invention, a polymethine type donor-acceptor dye is formed upon reduction. Thus, in an embodiment, the chemical compound of the present invention is a compound undergoing a bathochromic shift upon reduction. In a further embodiment, the reduced form of said chemical compound has an absorption maximum at a wavelength of <NUM> to <NUM>.

Advantageously, it was found in the work underlying the present invention, that the chemical compounds described herein are compounds undergoing a bathochromic shift upon reduction and that the redox potential of said compounds makes them suited for receiving redox equivalents in particular from reduced nicotine adenine dinucleotide (NADH). Moreover, it was found that said compounds have at least one absorption maximum in the range of visible light, enabling visual inspection and/or photometric determination of their redox state at a wavelength where interference from other compounds comprised, e.g. in blood samples, is minimal or at least acceptable. Some of the compounds also are fluorogenic upon reduction and, therefore, can be used for determining or detecting reducing agents by fluorescence spectroscopy or fluorescence imaging (see, e.g., <NPL>).

The definitions made above apply mutatis mutandis to the following. Additional definitions and explanations made further below also apply for all embodiments described in this specification mutatis mutandis.

As indicated above, the present invention relates to a chemical compound or a salt or solvate thereof, said chemical compound comprising a heterocyclic group (Het) covalently bound to a π-acceptor group (Acc), having the general structure of formula (VI)
<CHM>.

The term "chemistry matrix" is known to the skilled person and may relate to a mixture of compounds comprising the aforesaid chemical compound and a redox cofactor as described herein below. The chemical compounds indicated above may be present in a chemistry matrix, which may further comprise an oxidoreductase as described herein below. It is understood by the skilled person that such a composition may comprise additional components, e.g. buffer components (e.g., of phosphate buffered saline, Tris buffer, citrate buffer, glycerine phosphate buffer, or Good's buffer) or other salts, detergents, including the components as specified herein below.

The term "redox cofactor" or "cofactor", as used herein, relates to a redox-active flavine, nicotinamide or pyrroloquinoline quinone (PQQ) coenzyme. The skilled person knows how to select one of the aforesaid coenzymes appropriately, depending on the oxidoreductase selected. , For example, the flavine, nicotinamide or PQQ coenzyme may be flavine adenine dinucleotide (FAD), flavine mononucleotide (FMN), or PQQ, or a derivative of one of the aforesaid compounds. Alternatively, the redox cofactor may be nicotinamide adenine dinucleotide (NAD+), nicotinamide adenine dinucleotide phosphate (NADP+), or a derivative thereof. Further NAD+ or NADP+ derivatives are stabilized NAD+ or NADP+ derivatives, for example, carbacyclic derivatives, including, for example, carbaNAD+ or carbaNADP+, as disclosed, e.g., in <NPL>)), <NPL>)), <CIT>, <CIT>, <CIT> and <CIT>. The redox cofactor may be reduced NAD+, NADP+, carbaNAD+, or carbaNADP+, i.e., for example, NADH, NADPH, carbaNADH, or car-baNADPH. As will be understood by the skilled person, the term "comprising a redox cofactor", may include cases where at least one redox cofactor is added as such to a mixture of compounds, as well as cases where at least one redox cofactor is present in a chemistry matrix as a constituent of a different compound added to said mixture of compounds, e.g., for example, as a constituent of one or more cell(s) added to said mixture of compounds.

As used herein, the term "heterocyclic group" relates to a chemical side chain according to formula (IX), as depicted above. In an embodiment, the heterocyclic group is a redox active heterocyclic group. Redox active heterocyclic groups are known from the prior art (<NPL>; <NPL>; <NPL>; <NPL>.

Side chain Acc is covalently connected to the heterocyclic group directly or via one or more eth-enyl (vinyl) or ethenylene (vinylene) groups. Acc is -(C=C(CN)<NUM>) or a π-acceptor group of the general formula (XVI)
<CHM>.

As used in the context of the structural formulas of the present specification, k relates to an integer selected from <NUM> and <NUM>. In an embodiment, k is <NUM>. Also in an embodiment, the sum of l and k, in an embodiment, is <NUM> or less, in a further embodiment, the sum of l and k is <NUM> or less; in a further embodiment, the sum of l and k is <NUM>.

As used herein, R<NUM> relates to an organic side chain, in an embodiment methyl, in a further embodiment, ethyl, in a further embodiment, phenyl. R<NUM> is H or an organic side chain. In an embodiment, R<NUM> and R<NUM> together form a bridge to form an, optionally substituted, <NUM>- to <NUM>-membered heterocycloalkyl or heteroaryl ring.

According to the present invention, the side chain comprising the π-acceptor group is covalently linked to the ring system via the C3 atom of said heterocyclic group (Het). Further embodiments of attachment of the π-acceptor group are specified elsewhere herein.

In an embodiment, the chemical compound is a compound comprising or consisting of a structure selected from formulas (XXV) to (XXVII):
<CHM>
<CHM>.

A chemistry matrix can be provided, for example, by dissolving the components of the present invention first in a solvent or mixture of solvents. In a further embodiment, said solvent or mixture of solvents is subsequently removed by a suitable treatment such that the remaining composition is essentially free of the said solvent or solvent mixture. Suitable treatments to be in an embodiment envisaged by the present invention include heat treatment, evaporation techniques, freeze drying and the like. In an embodiment, the envisaged treatment is heat treatment and, in particular, heat treatment under the following conditions: heat treatment at about <NUM> or more for approximately <NUM> to <NUM> minutes or at about <NUM> for approximately <NUM> to <NUM> minutes with heat circulation; thickness of the chemistry matrix of <NUM> to <NUM> micrometers or less; at a pressure of <NUM> bar or <NUM> bar. Moreover, it will be understood that in order to keep the chemistry matrix under dry conditions, storage is, in an embodiment, carried out in the presence of a drying agent, i.e., a desiccant. Suitable drying agents, in an embodiment, encompass silica gel, zeolites, calcium carbonate or magnesium sulfate. The compounds according to the invention can also be polymerized or copolymerized or incorporated in a polymer to form redoxactive films.

The terms "oxidoreductase" and "oxidoreductase enzyme", as used herein, refer to a polypeptide which is capable of catalyzing the, for example, specific, oxidation or reduction of a substrate by transferring hydrides (H-) as redox equivalents to or from a redox cofactor as referred to herein elsewhere. For example, the oxidoreductase is a dehydrogenase, i.e. a polypeptide which is capable of catalyzing the oxidation of a substrate by transferring hydrides (H-) as redox equivalents to an acceptor molecule, in an embodiment, to a redox cofactor as referred to herein elsewhere. Dehydrogenases are, for example, those which depend on a redox cofactor (or sometimes referred to as co-enzyme) such as pyrroloquinoline quinone (PQQ) or a derivative thereof, nicotinamide-adenine-dinucleotide (NAD) or a derivative thereof, or a flavine cofactor, such as flavin-adenine-dinucleotide (FAD) or flavine mononucleotide (FMN), or a derivative thereof. Further dehydrogenases are, in particular, lactate dehydrogenase (EC number <NUM>. <NUM> or <NUM>. <NUM>), glucose dehydrogenases (see below), alcohol dehydrogenase (EC number <NUM>. <NUM> or <NUM>. <NUM>), L-amino acid dehydrogenase (EC number <NUM>. <NUM>), glycerol dehydrogenase (EC number <NUM>. <NUM>), malate dehydrogenase (EC number <NUM>. <NUM>), <NUM>-hydroxybutyrate dehydrogenase (EC number <NUM>. <NUM>), or sorbitol dehydrogenase (EC number <NUM>.

For example, said oxidoreductase is a glucose dehydrogenase. For example, said glucose dehydrogenase is selected from the group consisting of: glucose dehydrogenase (EC number <NUM>. <NUM>), quinoprotein glucose dehydrogenase (EC number <NUM>. <NUM>), in particular, pyrroloquinoline quinone (PQQ)-dependent glucose dehydrogenase (EC number <NUM>. <NUM>), glucose-<NUM>-phospate dehydrogenase (EC number <NUM>. <NUM>), nicotinamide adenine dinucleotide (NAD)-dependent glucose dehydrogenase (EC number <NUM>. <NUM>) and flavin adenine dinucleotide (FAD)-dependent glucose dehydrogenase (EC number <NUM>. <NUM>) or enzymatically active mutants thereof.

Enzymatically active mutants of the aforementioned enzymes can be obtained by substituting, adding or deleting one or more amino acids from the amino acid sequences reported for the aforementioned wild type enzymes in the prior art as recited before. Further envisaged as mutants are the mutants of the PQQ-dependent glucose dehydrogenase having an improved substrate specificity compared to their wild type counterparts as disclosed in <CIT> or <CIT>. Further mutants are those disclosed in Baik et al (<NPL>), Vasquez-Figuera et al. (<NPL>), and <CIT>.

Alternatively, a glucose dehydrogenase (E. <NUM>) mutant disclosed in <CIT> (p. <NUM>) or <CIT>, having a mutation at least at amino acid positions <NUM>, <NUM> and/or <NUM> is envisaged as mutant. Further mutations envisaged at these amino acid positions are substitutions of Glu96Gly, Glu170Arg or Lys and/or Lys252Leu, e.g. the combination Glu170Lys / Lys252Leu. In a further embodiment, said mutations are mutations Glu170Arg and Gln252Leu in glucose dehydrogenase from Bacillus subtilis.

As will be realized by the skilled person, the chemical compounds according to the present invention can be used as reporter dyes in cases where an oxidoreductase is used as a reporter enzyme, in an embodiment, e.g. in an immunoassay or in an enzymatic determination of an analyte. Moreover, the chemical compounds can be used as substitute of tetrazolium salts for cell viability testing, with the benefit of higher extinction coefficients. Moreover, if the chemical compounds are modified, they can be used as a labelling reagent.

The term "redox equivalents" as used herein relates to the concept commonly used in redox chemistry well known to the skilled person. For example, the term relates to electrons which are transferred from a substrate of the oxidoreductase to the redox cofactor, and/or from said redox cofactor to a redox mediator, and/or from said redox mediator to and indicator compound and/or to an electrode.

A chemistry matrix may further comprises at least one detergent, swelling agent, film-forming agent, and/or solid particle. Suitable stabilizers, detergents, swelling agents, film forming agents, oxidizing agents, and/or solid particles to be used in the composition of the invention are known to the skilled artisan. For example, the said at least one detergent is selected from the group consisting of: sodium-N-methyl-N-oleoyltaurat, N-octanoyl-N-methyl-glucamid, Mega <NUM> (N-methyl-N-octanoylglucamide), dioctylsodium sulfosuccinate (DONS), Rhodapex® (in an embodiment CO-<NUM> or CO-<NUM>). For example, said at least one swelling agent is selected from the group consisting of: methyl vinyl ether maleic acid anhydride copolymer, xanthan gum and methyl vinyl ether maleic acid copolymer. For example, said at least one film-forming agent is selected from the group consisting of: polyvinylpropionate dispersions, polyvinyl esters, polyvinyl acetates, polyacrylic esters, polymethacrylic acid, polyvinyl amides, polyamides, polystyrene and mixed polymerisates are also suitable such as of butadiene, styrene or maleic acid ester. For example, said at least one solid particle is selected from the group consisting of: silica particles, in particular, silicon dioxide, sodium silicates or aluminum silicates, kieselguhr, metal oxides, in particular, titan oxide and/or aluminum oxide, synthetic oxide materials, in particular, nanoparticles of oxide materials such as nanoparticles of silicon dioxide, aluminum oxide, or titan oxide, Kaolin, powder glass, amorphous silica, calcium sulfate, and barium sulfate.

The chemical compound of the present invention and/or a chemistry matrix thereof may be used in a test element.

The term "test element", as used herein, relates to a unit comprising a test chemistry, for example, a dry test chemistry, on a solid support. The test chemistry may be comprised in a test field as described herein below. The test element may further comprise a capillary element, adapted for taking up and/or transporting a liquid by capillary action, for example, to a test field. The test element may be selected from an optical test element and an electrochemical test element. The test element may further optionally comprise at least one puncture element, such as a lancing element, which, in an embodiment, may be mounted movably with regard to the test field, in order to perform a puncture motion, a sampling motion or a lancing motion, thereby generating an incision in a skin surface. The test field may remain in a fixed position during the puncture, sampling or lancing motion, wherein a sample of a body fluid is transferred onto the test field, such as by a capillary action and/or by pressing the puncture element or a part thereof onto the test field after the puncture, sampling or lancing motion. The test element may be a test strip, a test tape, or a test disc.

The term "test field" relates to a continuous or discontinuous amount of test chemistry, which, for example, is held by at least one carrier, such as by at least one carrier film. Thus, the test chemistry may form or may be comprised in one or more films or layers of the test field, and/or the test field may comprise a layer setup having one or more layers, wherein at least one of the layers comprises the test chemistry. Thus, the test field may comprise a layer setup disposed on a carrier, wherein a sample of a body fluid may be applied to the layer setup from at least one application side, such as from an edge of the test field and/or from an application surface of the test field. The test field may have a multilayer setup, the multilayer setup comprising at least one detection layer having the at least one test material and further comprising at least one separation layer adapted for separating off at least one particulate component contained in the body fluid, wherein the separation layer is located between the detection layer and the capillary element. It is understood by the skilled person that all layers present optionally between the body fluid and the test field are selected as to allow passage of at least the analyte.

For example the test element may be an optical test element, i.e. a test element adapted to change at least one optical property in the presence of the analyte. Alternatively, at least one chemistry matrix comprised in the test element may perform at least one optically detectable detection reaction in the presence of the analyte. In another alternative, the detection reaction may be a redox reaction. In another alternative, the detection reaction may produce redox equivalents and/or electrons as intermediates and/or products. In another alternative, the optically detectable signal produced by the detection reaction may be proportional to the amount and/or to the concentration of the analyte in the sample.

The test element may be adapted to change at least one optical property in the presence of an analyte, , or the compound of the present invention may change at least one optical property in the presence of an analyte. It is, however, also envisaged that the test element may additionally comprise an indicator reagent. The term "indicator reagent", as used herein, relates to a compound changing at least one optical property dependent on, proportional to, the redox state of the chemical compound of the present invention comprised in a test element. IThe indicator reagent may be an optical indicator substance, which performs at least one optically detectable property change when the chemical compound of the present invention comprised in a chemistry matrix changes its redox state in the presence of the analyte. Thus, the at least one indicator reagent, may comprise one or more dyes performing a change in an optical property indicative of the enzymatic reaction of the at least one enzyme and the analyte.

The term "optical property", as used herein, relates to a property, which can be detected by an optical instrument. Specifically, the optical property may be or may comprise at least one property selected from the group consisting of: a reflection property, a transmission property, an emission property, a scattering property, a fluorescence property, a phosphorescence property, a diffraction property, and a polarization property. In an embodiment, an optical property as referred to herein refers to a property of a chemical compound which can be optically detected such as light absorption, light emission, light remission, or properties associated therewith. It will be understood that such a change of at least one optical property as used herein encompasses the detection of the presence of a property which was not detectable before, the detection of the absence of a property which has been detected before, and the detection of quantitative changes of a property, i.e., the detection of the change of the signal strength which correlates to the extent of the change of the at least one optical property. Further optical properties envisaged by the present invention are color, fluorescence, luminescence, or refractometry. Methods of converting the optical property as defined above into a physical signal which can be read as a measurement value are well known in the art and are described, e.g., in <CIT>, <CIT>, and <CIT>.

The optical property of the chemical compound and/or of an indicator reagent, according to the present invention, may change dependent on the activity of an enzyme. Thus, the change of the optical property may only occur if the enzyme catalyzes the detection reaction. For example, the change of optical property is proportional to the number of catalytic cycles undergone by the enzyme present in the chemistry matrix. Thus, the change of optical property may be proportional to the number of analyte molecules converted by the enzyme.

A test element may be an electrochemical test element and the chemical compound of the present invention may have the function of being a redox mediator, for example mediating transfer of redox equivalents between a redox cofactor and an electrode of the test element. Accordingly, the test element may comprise at least two electrodes contacting, directly or indirectly, the chemistry matrix, as specified elsewhere herein. Suitable electrodes, electrode setups, and modes of operation are known to the skilled person and are described, e.g. in <CIT>, <CIT>, <CIT> and references cited therein. Moreover, ia chemistry matrix may include one or more chemical reagents for reacting with the analyte to produce an electrochemical signal that represents the presence of the analyte in the sample fluid. For example, the one or more chemical reagents for reacting with the analyte to produce an electrochemical signal that represents the presence of the analyte in the sample fluid may comprise a redox cofactor and/or an oxidoreductase as described herein above. For example, electrochemical properties include amperometric or coulometric responses indicative of the concentration of the analyte. See, for example, <CIT>, <CIT> and <CIT>.

An electrochemical test element may comprise at least two electrodes contacting the chemistry matrix comprised in said test element, or contacting means conductively connected to said test chemistry. For example, the means conductively connected to a chemistry matrix may be a layer of a test strip connected to a chemistry matrix to enable diffusion of a redox cofactor and/or of a redox mediator through said layer. Alternatively, the means conductively connected to a chemistry matrix may be a layer of a test strip at least partially overlaying and/or underlaying said chemistry matrix to enable diffusion of a redox cofactor and/or of a redox mediator through said layer.

The electrochemical property may change dependent on the activity of an oxidoreductase. Thus, for example, the change of the electrochemical property may only occur if the oxidoreductase catalyzes the detection reaction. For example, the change of electrochemical property may be proportional to the number of catalytic cycles undergone by the oxidoreductase present in a chemistry matrix. Thus, for example, the change of electrochemical property may be proportional to the number of analyte molecules converted by the oxidoreductase.

A test element may be is a combined optical and electrochemical test element. Accordingly, the test element may have the structural features of an optical test element as well as the structural features of an electrochemical test element, i.e., for example, at least two electrodes. Various formats have been described for combined test elements; e.g. <CIT> Aldescribes a dual sensor with two reaction zones, making simultaneous electrochemical and colorimetric readings possible. Also, <CIT> teaches a test strip with multiple reaction zones, and <CIT> discloses a hybrid test strip with separate reaction zones for colorimetric and electrochemical detection.

Moreover, the present invention relates to a use of a chemical compound as structurally defined herein, in diagnosing hyperglycemia, hypoglycemia, normal glucose levels, cell viability and/or microbial contamination as outlined in more details below.

The term "test" is understood by the skilled person and relates to any process or method for assessing qualitatively or quantitatively the presence or absence of a compound of interest in a mixture of compounds.

An analytical test may be a test for assessing qualitatively or quantitatively the presence or absence of a redox cofactor as specified elsewhere herein, for example, of a reduced redox cofactor. Accordingly, an analytical test may be a cell viability test, for example, an in vitro cell viability test. However, any potential test may also include assessing the presence of reduced redox cofactors, e.g. in testing for microbial contamination.

Accordingly, the present invention also relates to a use of a chemical compound comprising a heterocyclic group (Het) covalently bound to a π-acceptor group (Acc) according to the present invention for analyzing the viability of cells.

An analytical or diagnostic test may comprise qualitative and/or quantitative determination of any biological or chemical analyte detectable by optical or/and electrochemical means. For example, the analyte may be comprised in a test sample of a subject, for example, a test sample of a body fluid. , Alternatively a diagnostic test comprises determining a glucose concentration in a test sample. For example, a diagnostic test comprises determining a glucose concentration in a test sample from a subject suffering from diabetes or suspected to suffer from diabetes. A diagnostic test may comprise monitoring blood glucose concentrations, for example, in a subject suffering from diabetes or suspected to suffer from diabetes. A diagnostic test is an in vitro test.

The term "analyte", as used herein, relates to a chemical compound present in a test sample of a subject, for example, in a body fluid. For example, the analyte is a small molecule, i.e., for example, the analyte is not a biological macromolecule. Alternatively, the analyte is an organic molecule, for example, an organic molecule capable of undergoing a redox reaction in the presence of a test chemistry as described herein above. For example, the analyte is a molecule of the subject's metabolism. Also for example, the analyte is a low molecular weight chemical compound, such as a chemical compound with a molecular mass of less than <NUM> u (<NUM> Da; <NUM>×<NUM>-<NUM> kg). For example, the analyte may be selected from the list consisting of malate, ethanol, ascorbic acid, cholesterol, glycerol, urea, <NUM>-hydroxybutyrate, lactate, pyruvate, triglycerides, ketones, liver parameters, creatinine, HDL; , or the analyte is blood glucose.

As used herein, the term "subject" relates to a vertebrate. A subject is preferably a mammal, more preferably a mouse, rat, cat, dog, hamster, guinea pig, sheep, goat, pig, cattle, or horse. More preferably, the subject is a primate, more preferably a human. The subject may be afflicted or suspected to be afflicted with a disease or condition associated with a measurable deviation from normal of at least one analyte, for example, the subject may be afflicted with diabetes.

As used herein, the term "body fluid" relates to all bodily fluids of a subject known to comprise or suspected to comprise an analyte, including blood and blood products, plasma, serum, lacri-mal fluid, urine, lymph, cerebrospinal fluid, bile, stool, sweat, interstitial fluid, and saliva. For example, the body fluid is plasma or serum or blood.

The term "test sample" is understood by the skilled person and relates to any suitably sized sub-portion of a tissue or, in an embodiment, of a body fluid of a subject. Body fluid test samples can be obtained by well known techniques including, e.g., venous or arterial puncture, epidermal puncture, and the like.

The term "diabetes" or "diabetes mellitus", as used herein, refers to disease conditions in which the glucose metabolism is impaired. Said impairment results in hyperglycemia. According to the World Health Organization (WHO), diabetes can be subdivided into four classes. Type <NUM> diabetes is caused by a lack of insulin. Insulin is produced by the so called pancreatic islet cells. Said cells may be destroyed by an autoimmune reaction in Type <NUM> diabetes (Type 1a). Moreover, Type <NUM> diabetes also encompasses an idiopathic variant (Type 1b). Type <NUM> diabetes is caused by an insulin resistance. Type <NUM> diabetes, according to the current classification, comprises all other specific types of diabetes mellitus. For example, the beta cells may have genetic defects affecting insulin production, insulin resistance may be caused genetically or the pancreas as such may be destroyed or impaired. Moreover, hormone deregulation or drugs may also cause Type <NUM> diabetes. Type <NUM> diabetes may occur during pregnancy. In an embodiment, diabetes as used herein refers to diabetes Type <NUM> or, in a further embodiment, Type <NUM>. According to the German Society for Diabetes, diabetes is diagnosed either by a plasma glucose level being higher than <NUM>/dl in the fasting state or being higher than <NUM>/dl postprandial. Further diagnostic techniques for diagnosing diabetes, which may be used in conjunction with or in addition to the diagnostic use of the present invention are well known in the art and are described in standard text books of medicine, such as Stedman or Pschyrembl.

It is understood by the skilled person that in diabetes, blood glucose levels have to be checked on a regular basis, in order to avoid and/or take countermeasures against hyperglycemia, e.g. after meals, or to avoid and/or take countermeasures against hypoglycemia, e.g. after administration of insulin. Accordingly, the present invention relates, as indicated above, also to a chemical compound of the present invention for use in diagnosing hyperglycemia, hypoglycemia, or normal glucose levels.

When used for diagnosis as described above, a method for determining the amount of an analyte in a test sample may be used, comprising.

The method is an in vitro method. Moreover, it may comprise steps in addition to those explicitly mentioned above. For example, further steps may relate, e.g., to obtaining a test sample for step a), or measuring at least one optical property of the chemical compound, the chemistry matrix, or the test element in the presence of said test sample in step b). Moreover, one or more of said steps may be performed by automated equipment. It is also understood by the skilled person that one or more steps of the method, e.g. the step of estimating the amount of redox equivalents liberated or consumed, may be repeated.

The term "determining" relates to measuring of the amount of an analyte in a sample, in an embodiment, semi-quantitatively or, in a further embodiment, quantitatively.

Methods of measuring the amount of redox equivalents, in an embodiment, electrons, liberated or consumed are known from the prior art. For example, the amount of redox equivalents liberated or consumed may be measured by means of an optical or an electrochemical sensor. For example, measuring the amount of redox equivalents liberated or consumed may comprise detecting an optical property of a compound of the present invention as specified herein above.

The method for determining the amount of an analyte in a test sample may be a method for determining blood glucose levels in a subject, comprising.

It is understood by the skilled person that in case elevated levels of blood glucose are determined in a sample or, in an embodiment, in more than one sample from the same subject, the method of determining blood glucose levels may be a method assisting in diagnosing diabetes.

As used herein, the term "elevated level of blood glucose" relates to blood glucose concentrations of more than <NUM>/dL, in an embodiment, more than <NUM>/dL; and the term "low levels of blood glucose" relates to blood glucose concentrations of less than <NUM>/dL, in an embodiment, less than <NUM>/dL.

A system for determining the amount of an analyte in a sample may comprise.

The term "device" is known to the skilled person and relates to technical equipment comprising at least one sensor for measuring the amount of redox equivalents liberated or consumed by a compound of the present invention. For example, said sensor may be an optical and/or an electrochemical sensor; said sensors are known to the skilled person.

Thus, the following embodiments are particularly envisaged:.

Further optional features and embodiments of the invention will be disclosed in more detail in the subsequent description of examples. The respective optional features disclosed therein and in the definitions may be realized in an isolated fashion as well as in any arbitrary feasible combination, as the skilled person will realize. The scope of the invention is not restricted by the examples.

To a solution of <NUM>-Quinolinecarbaldehyde (XXXIII) (<NUM>, <NUM> mmol) in <NUM> EtOH and <NUM> NaOH (<NUM>% in H<NUM><NUM>) Acetophenone (XXXIV) (<NUM>, <NUM> mmol) was added. The mixture was stirred at room temperature for <NUM> and subsequently concentrated under reduced pressure. The remaining crude product was purified by silica gel chromatography (n-hexane/acetone; <NUM>:<NUM>) obtaining <NUM> (<NUM>%) of the title compound.

To a solution of (E)-<NUM>-phenyl-<NUM>-quinolin-<NUM>-yl-propenone (XXXV) (<NUM>, <NUM> mmol) in <NUM> acetone dimethylsulfate (<NUM>, <NUM> mmol) was added. The mixture was stirred <NUM> at room temperature. The obtained suspension was filtered and the remaining precipitate was washed <NUM> times with acetone. The crude product was purified by preparative HPLC (H<NUM><NUM>/CH<NUM>CN) obtaining <NUM> (<NUM>%) of the title compound (XXII).

Two solutions of the redoxindicator <NUM>-methyl-<NUM>-((E)-<NUM>-oxo-<NUM>-phenyl-propenyl)-quinolinium methosulfate (<NUM>, <NUM> mmol) in <NUM> water were each treated with an excess of NADH (disodium salt) or sodium ascorbate, respectively. The solution treated with NADH changed rapidly from nearly colorless to orange. After a few minutes, a larger amount of an orange precipitate was obtained, probably the insoluble dihydrochinoline. In contrast, the solution treated with ascorbate showed only a pale orange color. Even after <NUM> no precipitate was found. Thus, turnover rates of MOPPQ with NADH are much higher than with ascorbate.

A suspension of <NUM>-ethoxyphenazine-<NUM>-carboxylic acid (XXXVI) (<NUM>, <NUM> mmol) (synthesized from N-(<NUM>,<NUM>-difluorophenyl)-<NUM>-nitroanthranilic acid by a method in <NPL>) in DMF (<NUM>) was treated with <NUM>,<NUM>'-carbonyldiimidazole (CDI) (<NUM>, <NUM> mmol), and the mixture was stirred at <NUM> for <NUM>. After cooling, the mixture was diluted with DCM/petroleum ether (<NUM>:<NUM>) to complete precipitation of the imidazolide, which was collected, washed with petroleum ether, dried, dissolved in THF (<NUM>) then slowly added to a solution of NaBH<NUM> in H<NUM>O (<NUM>). After stirring for <NUM>, the mixture was neutralized by dropwise addition of concd HCl and then extracted with EtOAc. The organic layer was washed with aqueous Na<NUM>CO<NUM>, water, dried (Na<NUM>SO<NUM>), and evaporated, to give (<NUM>-ethoxyphenazin-<NUM>-yl)methanol (XXXVII) (<NUM>).

A mixture of (<NUM>-ethoxyphenazin-<NUM>-yl)methanol (XXXVII) (<NUM>, <NUM> mmol), activated manganese (IV) oxide (<NUM>, <NUM> mmol) and DCM (<NUM>) was stirred at room temperature under an argon atmosphere for <NUM>. After this time, the reaction was filtered through a pad of silica gel and concentrated. The residue was dissolved in EtOAc and the solution obtained was washed with aqueous Na<NUM>CO<NUM>, water, dried (Na<NUM>SO<NUM>), evaporated and dried under vacuum for <NUM> to give <NUM>-ethoxyphenazine-<NUM>-carbaldehyde (XXXVIII) (<NUM>) as a yellow solid.

A mixture of <NUM>-ethoxyphenazine-<NUM>-carbaldehyde (XXXVIII) (<NUM>, <NUM> mmol) and <NUM>,<NUM>,<NUM>,<NUM>-tetramethyl-<NUM>-indolium iodide (XXXIX) (<NUM>, <NUM> mmol) in ethanol (<NUM>) was heated to reflux under an argon atmosphere for <NUM> in the presence of piperidine (<NUM>µL, <NUM> mmol). The reaction mixture was allowed to cool slowly to room temperature, and a red precipitate was filtered off, washed with cold ethanol, then with diethyl ether and dried. <NUM>, red powder was obtained.

A mixture of quinoline-<NUM>-carbaldehyde (XXXIII) (<NUM>, <NUM> mmol) and <NUM>,<NUM>-dimethyl-<NUM>,<NUM>,<NUM>,<NUM>-tetrahydro-<NUM>-pyrido[<NUM>,<NUM>-a]indolium hexafluorophosphate (XLI) (<NUM>, <NUM> mmol) (synthesized from <NUM>,<NUM>,<NUM>-trimethyl-<NUM>-indole by a method in <NPL>) in ethanol (<NUM>) was heated to reflux under an argon atmosphere for <NUM> in the presence of piperidine (<NUM>µL, <NUM> mmol). The reaction mixture was allowed to cool slowly to room temperature, and a precipitate was filtered off, washed with cold ethanol, then with diethyl ether and dried. <NUM>, yellow powder was obtained.

The comparative indolium salts listed in Table <NUM> are obtained analogously to comparative examples <NUM>-<NUM>. All comparative indolium salts are indicated by "*".

To a solution of <NUM>,<NUM>,<NUM>-trimethyl-<NUM>-[(E)-<NUM>-(quinolin-<NUM>-yl)ethenyl]-<NUM>-indolium iodide (XLV) (<NUM>, <NUM> mmol) in <NUM> of dry DCM was added TfOMe (<NUM>µL, <NUM> mmol) in dry DCM (<NUM>) dropwise under an argon atmosphere. After the mixture was stirred for <NUM> at room temperature, a precipitate was filtered off, washed with DCM (<NUM> × <NUM>) and then with diethyl ether, and dried. <NUM>, yellow powder was obtained.

The comparative and inventive diquaternary salts listed in Table <NUM> are obtained by reacting indolium salts (from examples <NUM>-<NUM>) with various triflate alkylating agents analogously to example <NUM>. The temperature and time of reaction can usually be varied over wide ranges. The product is crystallized from a suitable solvent and, if required, the anion can be changed by conventional procedures, for example by the use of ion exchange resins. Comparative diquaternary salts are identified in Table <NUM> with "*".

The following were mixed in a cuvette: <NUM>µL of <NUM> solution of a comparative indicator (<NUM>-methyl-<NUM>-[(E)-<NUM>-(<NUM>,<NUM>,<NUM>-trimethyl-<NUM>-indolium-<NUM>-yl)ethenyl]quinolinium iodide trifluoromethanesulfonate) in distilled water, <NUM>µL of <NUM> phosphate buffer pH <NUM>, <NUM>µL of <NUM> NADH solution in distilled water. A UV/Vis spectrum (<NUM>-<NUM>) was recorded every <NUM> sec for a <NUM> after addition of NADH (resolution <NUM>) (<FIG>). No further color change could be measured after <NUM> sec.

UV/Vis spectral properties of further comparative indicators and indicators according to the invention listed are in Table <NUM>, wherein comparative indicators are indicated by "*".

The following were mixed in a cuvette: <NUM>µL of <NUM> solution of a comparative indicator (<NUM>-methyl-<NUM>-[(E)-<NUM>-(<NUM>,<NUM>,<NUM>-trimethyl-<NUM>-indolium-<NUM>-yl)vinyl]quinolinium iodide trifluoromethanesulfonate) in distilled water, <NUM>µL of <NUM> phosphate buffer pH <NUM>, <NUM>-<NUM>µL of <NUM> NADH solution in distilled water. Change in absorbance at <NUM> was recorded after <NUM> (<FIG>).

Two solutions of the redoxindicators <NUM>-methyl-<NUM>-[(E)-<NUM>-(<NUM>,<NUM>,<NUM>-trimethyl-<NUM>-indolium-<NUM>-yl)ethenyl]quinolinium iodide trifluoromethanesulfonate (<NUM> mmol) in <NUM> of <NUM> phosphate buffer pH <NUM> were each treated with <NUM>µL of <NUM> NADH (disodium salt) or sodium ascorbate solutions in distilled water, respectively. The absorbance at <NUM> was measured in relation to time (<FIG>). The solution treated with NADH changed rapidly from nearly colorless to pink. In contrast, the solution treated with ascorbate did not change color. Thus, turnover rates of <NUM>-methyl-<NUM>-[(E)-<NUM>-(<NUM>,<NUM>,<NUM>-trimethyl-<NUM>-indolium-<NUM>-yl)ethenyl]quinolinium iodide trifluoromethanesulfonate with NADH are much higher than with ascorbate.

The following were mixed in a cuvette: <NUM>µL of <NUM> solution of an indicator (<NUM>-methyl-<NUM>-[(E)-<NUM>-(<NUM>,<NUM>,<NUM>-trimethyl-<NUM>-indolium-<NUM>-yl)vinyl]quinolinium iodide trifluoromethanesulfonate) in <NUM> phosphate buffer pH <NUM>, <NUM>µL of glucose dehydrogenase <NUM> (GlucDH2) solution (in <NUM> phosphate buffer pH <NUM> containing <NUM> NAD+) at a concentration of <NUM> U/ml, <NUM>µL of <NUM> solution of glucose in distilled water. A UV/Vis spectrum (<NUM>-<NUM>) was recorded every <NUM> for a <NUM> after addition of glucose (resolution <NUM>) (<FIG>).

The reaction mixture was the same as in Measurement <NUM>, except for <NUM>-<NUM>µL samples of <NUM> solution of glucose in distilled water were used. The absorbance at <NUM> was recorded every <NUM> sec for a <NUM> after addition of glucose (<FIG>).

Conditions were the same as in Measurement <NUM>, with carbaNAD replacing NAD. The absorbance at <NUM> was recorded every <NUM> sec for a <NUM> after addition of glucose (<FIG>).

<NUM>-Methyl-<NUM>-[(E)-<NUM>-(<NUM>,<NUM>,<NUM>-trimethyl-<NUM>-indolium-<NUM>-yl)ethenyl]quinolinium iodide trifluoromethanesulfonate, evaluation of extinction coefficient (ε) under pseudo-first-order reaction conditions.

The following were mixed in a cuvette: <NUM>µL of <NUM> solution of <NUM>-methyl-<NUM>-[(E)-<NUM>-(<NUM>,<NUM>,<NUM>-trimethyl-<NUM>-indolium-<NUM>-yl)ethenyl]quinolinium iodide trifluoromethanesulfonate in distilled water, <NUM>µL of <NUM> phosphate buffer pH <NUM>, <NUM>-<NUM>µL of <NUM> NADH in distilled water. Change in absorbance at <NUM> was recorded after <NUM>, when no further color change could be measured (<FIG>, <FIG>).

<FIG> shows that concentration of the reduced form of <NUM>-methyl-<NUM>-[(E)-<NUM>-(<NUM>,<NUM>,<NUM>-trimethyl-<NUM>-indolium-<NUM>-yl)ethenyl]quinolinium iodide trifluoromethanesulfonate is proportional to the initial NADH concentration. Using the equation <MAT> an ε value for the reduced form of <NUM>-methyl-<NUM>-[(E)-<NUM>-(<NUM>,<NUM>,<NUM>-trimethyl-<NUM>-indolium-<NUM>-yl)ethenyl]quinolinium iodide trifluoromethanesulfonate of <NUM>-<NUM>cm-<NUM> was calculated from the slope of the trend line. This ε value is nine times greater than those of the reduced form of MTT (<NPL>).

The CVs of the comparative and inventive compounds synthesized in example <NUM> and <NUM> were recorded vs. the Ag/AgCl reference electrode in a phosphate buffer pH <NUM> (Table <NUM>). Comparative compounds are indicated in Table <NUM> by "*".

The following were mixed in a cuvette: <NUM>µL of <NUM> solution of an indicator (<NUM>-methyl-<NUM>-[(E)-<NUM>-(<NUM>,<NUM>,<NUM>-trimethyl-<NUM>-indolium-<NUM>-yl)ethenyl]quinolinium iodide trifluoromethanesulfonate) in distilled water, <NUM>µL of <NUM> PIPES buffer pH <NUM>, <NUM>-<NUM>µL of <NUM> NADH solution in distilled water. The mixture was incubated for <NUM> at room temperature. Fluorescence (<NUM>-<NUM>) was recorded using excitation at <NUM>. (<FIG>, <FIG>).

Claim 1:
A chemical compound or a salt or solvate thereof comprising a heterocyclic group (Het) covalently bound to a π-acceptor group (Acc), having the general structure of formula (VI)
<CHM>
wherein Het comprises a structure
<CHM>
wherein R<NUM> is in an embodiment methyl, in a further embodiment ethyl, in a further embodiment phenyl,
wherein l is an integer between <NUM> and <NUM>, in an embodiment <NUM>, <NUM>, or <NUM>,
and wherein Acc is selected from -(C=C(CN)<NUM>), and an acceptor group of the general formula (XVI)
<CHM>
wherein
R<NUM> is an organic side chain, in an embodiment methyl, in a further embodiment ethyl, in a further embodiment phenyl,
k is an integer selected from <NUM> and <NUM>,
R<NUM> is H or an organic side chain,
R<NUM> is an organic side chain,
or wherein R<NUM> and R<NUM> together form a bridge to form a <NUM>- to <NUM>-membered heterocycloalkyl or heteroaryl ring,
wherein said π-acceptor group (Acc) is attached to the C3 atom of said heterocyclic group (Het).