Dieter Weiss

Experimental Evidence of the Occurrence of Intramolecular Electron Transfer in Catalyzed 1,2-Dioxetane Decomposition

The activation parameters for the thermal decomposition of 13 acridinium-substituted 1,2-dioxetanes, bearing an aromatic moiety, were determined and their chemiluminescence emission quantum yields estimated, utilizing in situ photosensitized 1,2-dioxetane generation and observation of its thermal decomposition kinetics, without isolation of these highly unstable cyclic peroxides. Decomposition rate constants show linear free-energy correlation for electron-withdrawing substituents, with a Hammett reaction constant of ρ = 1.3 ± 0.1, indicating the occurrence of an intramolecular electron transfer from the acridinium moiety to the 1,2-dioxetane ring, as postulated by the intramolecular chemically initiated electron exchange luminescence (CIEEL) mechanism. Emission quantum yield behavior can also be rationalized on the basis of the intramolecular CIEEL mechanism, additionally evidencing its occurrence in this transformation. Both relations constitute the first experimental evidence for the occurrence of the postulated intramolecular electron transfer in the catalyzed and induced decomposition of properly substituted 1,2-dioxetanes.

Synthesis and antiherpetic activity of carboxymethylated and sulfated hyaluronan derivatives.

Native high molecular weight hyaluronan (HMW-HA, MW=1×10(6) g/mol) and a thermally degraded low molecular weight hyaluronan (LMW-HA, MW=1.3-1.4×10(5) g/mol) were carboxymethylated providing products with degrees of carboxymethylation (DSCM) of up to 0.8. Sulfation of resulting carboxymethyl hyaluronan (CM-HA) and hyaluronan (HA) was performed by different sulfation procedures enabling the control of the degree of sulfation (DSS) in the obtained new carboxymethyl hyaluronan sulfates (CM-HA-S) and hyaluronan sulfates (HA-S), respectively, in a range between 0.9 and 3.3. Both carboxymethylation and sulfation were found to take place preferentially at the primary hydroxyl groups of HA. The antiviral activity of these synthesized HA derivatives was tested against Herpes simplex virus type 1. Both HA-S and CM-HA-S derivatives with high DSS values of about 3.0 exhibit a strong antiherpetic activity. The CM-HA derivatives were found to be not active and an additional effect of introduced carboxymethyl groups on the antiherpetic activity of CM-HA-S derivatives was not observed. In the case of HA-S, the antiviral efficacy can be correlated with the DSS and becomes stronger with increasing DSS values.

Novel luminescence dyes and ligands based on 4-hydroxythiazole

The condensation reaction of N-heteroaromatic nitriles with d,l-mercaptolactic acid results in the formation of 4-hydroxythiazoles. The products are sparingly soluble in most solvents in which they display only a weak fluorescence. However, upon derivatization of the OH-group by etherification, blue emitting luminescence dyes with high quantum yields and large stokes shifts were obtained. The luminescence of these thiazoles is affected by the 2-substituents and lies in the region of 410 nm, with quantum yields between 30% and 90%. Employing this method, not only new fluorophores were obtained, but also derivatives that offer good requirements for the construction of metal complexes due to their diazadiene substructure.

Chemiluminescence-based uphill energy conversion

The conversion of red excitation light into blue emission light (uphill energy conversion) using unstable 1,2-dioxetanes is described. The method is based on 1,2-dioxetane formation by red-light sensitized photooxygenation of adequate alkenes and subsequent blue-light emission due to thermal 1,2-dioxetane cleavage. The energy gain resulting from the chemical energy obtained in the transformation of an alkene into two carbonyl compounds transforms a red-light excitation laser beam into a blue-light chemiluminescence emission, producing thereby a formal anti-Stokes shift of 200–250 nm, opening up a whole spectrum of possible applications.

A new application of the “mild thiolation” concept for an efficient three-step synthesis of 2-cyanobenzothiazoles: a new approach to Firefly-luciferin precursors

2-Cyanobenzothiazoles (1) are important building blocks for natural products, functional dyes and innovative materials. Firefly luciferin (3), a natural product, is of outstanding importance in these areas. The substance was found in the beetle Photinus pyralis and is known to be a part of the most efficient chemiluminescence systems nowadays. For that reason, it plays a major role in applications used for medicinal diagnostics (1), biochemistry and forensic trace analysis (2) (Figure 1). 6-Methoxy-2-cyano-benzothiazole (1a) plays a key role as a precursor for preparations of 3. The first synthesis starting from p-anisidine (2a) was published in 1961 (3). More than 30 years later, Toya et al. (4) presented a one-step access to 1a which employed the commercially available 2-amino-6-methoxybenzothiazole (4) (Scheme 1). In subsequent years, a large number

Synthesis of some fenchyl-substituted alkenes and enol-ethers containing 3-oxyphenyl substituents by the Barton-Kellogg reaction

The synthesis of one fenchyl-substituted alkene and two enol-ethers, containing 3-oxyphenyl substituents by the Barton-Kellogg reaction is described. The tri-substituted aromatic fenchyl-alkene 1a was prepared in 53% yield from thiofenchone and a diazoanisole; whereas enol-ethers 1b and 1c were obtained (95 and 75% yield, respectively) using an inverse approach based on diazofenchone and aromatic thionoesters. A mixture of Z and E isomers was obtained in all cases; isomer attribution and quantification has been carried out by analysis of NMR spectroscopic data assisted by theoretical calculations (E/Z ratio: 1a = 0.72, 1b = 2.2, 1c = 1.8). Reaction proceeds with low stereoselectivity leading to the preferential formation of diastereoisomeric olefins and enol-ethers where the aromatic substituent resides at the side of the two fenchyl methyl groups.

2-Isopropyl-2-(6-meth­oxy-1,3-benzo­thia­zol-2-yl)-5,5-dimethyl-1,3-thia­zolidin-4-one

The title compound, C16H20N2O2S2, crystallizes with two enantiomers (A and B) in the asymmetric unit. The most noticeable difference between these two molecules is the relative orientation of the benzothiazole rings, with S—C—C—S torsion angles of −19.4 (2) (molecule A) and 100.6 (1)° (molecule B). The amide structure of the thiazolidinone rings leads to intermolecular hydrogen-bonded dimers of the R and S enantiomers.

2-(6-Bromo­benzo[d]thia­zol-2-yl)-5,5-di­methyl­thia­zol-4(5H)-one

The title compound, C12H9BrN2OS2, was obtained by reacting 6-bromobenzo[d]thiazole-2-carbonitrile in iso-propanol with ethyl 2-mercapto-2-methylpropanoate at reflux temperature for several hours. The resulting dimethyloxyluciferin derivative shows partial double-bond character of the carbon–carbon bond between the two heterocyclic moieties [C—C = 1.461 (3) Å]. This double bond restricts rotation around this C—C axis, therefore leading to an almost planar molecular structure [N—C—C—S torsion angle = 9.7 (3)°]. The five-membered thiazoline ring is not completely planar as a result of the bulky S atom [C—S—C—C torsion angle = 5.17 (12)°].