Matthias Heydenreich

Phosphorylation of C6- and C3-positions of glucosyl residues in starch is catalysed by distinct dikinases.

Glucan, water dikinase (GWD) and phosphoglucan, water dikinase (PWD) are required for normal starch metabolism. We analysed starch phosphorylation in Arabidopsis wild‐type plants and mutants lacking either GWD or PWD using 31P NMR. Phosphorylation at both C6‐ and C3‐positions of glucose moieties in starch was drastically decreased in GWD‐deficient mutants. In starch from PWD‐deficient plants C3‐bound phosphate was reduced to levels close to the detection limit. The latter result contrasts with previous reports according to which GWD phosphorylates both C6‐ and C3‐positions. In these studies, phosphorylation had been analysed by HPLC of acid‐hydrolysed glucans. We now show that maltose‐6‐phosphate, a product of incomplete starch hydrolysis, co‐eluted with glucose‐3‐phosphate under the chromatographic conditions applied. Re‐examination of the specificity of the dikinases using an improved method demonstrates that C6‐ and C3‐phosphorylation is selectively catalysed by GWD and PWD, respectively.

Two prenylated flavanones from stem bark of Erythrina burttii

Abstract From the stem bark of Erythrina burttii , two new flavanones were isolated and characterised as 5,7-dihydroxy-4′-methoxy-3′,5′-di-(3-methylbut-2-enyl)flavanone (trivial name, abyssinone V-4′-methyl ether) and 5,7-dihydroxy-4′-methoxy-3′-(3-hydroxy-3-methylbut-1-enyl)-5′-(3-methylbut-2-enyl)flavanone (trivial name, burttinone). In addition, seven known compounds were identified. Structures were determined on the basis of spectroscopic evidence.

Hyperphosphorylation of Glucosyl C6 Carbons and Altered Structure of Glycogen in the Neurodegenerative Epilepsy Lafora Disease

Laforin or malin deficiency causes Lafora disease, characterized by altered glycogen metabolism and teenage-onset neurodegeneration with intractable and invariably fatal epilepsy. Plant starches possess small amounts of metabolically essential monophosphate esters. Glycogen contains similar phosphate amounts, which are thought to originate from a glycogen synthase error side reaction and therefore lack any specific function. Glycogen is also believed to lack monophosphates at glucosyl carbon C6, an essential phosphorylation site in plant starch metabolism. We now show that glycogen phosphorylation is not due to a glycogen synthase side reaction, that C6 is a major glycogen phosphorylation site, and that C6 monophosphates predominate near centers of glycogen molecules and positively correlate with glycogen chain lengths. Laforin or malin deficiency causes C6 hyperphosphorylation, which results in malformed long-chained glycogen that accumulates in many tissues, causing neurodegeneration in brain. Our work advances the understanding of Lafora disease pathogenesis and suggests that glycogen phosphorylation has important metabolic function.

Glycopolymer vesicles with an asymmetric membrane

Direct dissolution of glycosylated polybutadiene-poly(ethylene oxide) block copolymers can lead to the spontaneous formation of vesicles or membranes, which on the outside are coated with glucose and on the inside with poly(ethylene oxide).

Study of the π-electron distribution in push-pull alkenes by 1H and 13C NMR spectroscopy. Part 4. The conformation and dynamic behaviour of substituted N-phenyl-2,3-dihydro-4(1H)-pyridones

Abstract The 1H and 13C NMR spectra of a number of differently substituted N-phenyl-2,3-dihydro-4(1H)-pyridones (integrated push-pull alkenes) were unequivocally assigned by means of a whole arsenal of 1D and 2D NMR spectroscopic methods. From the extracted NMR parameters and the results of accompanying quantum chemical calculations the preferred conformation of the compounds studied was found to be half-chair with the 1- and 2-substituents in pseudo-axial and axial conformations, respectively. By means of dynamic 13C NMR spectroscopy a dynamic process present was studied (restricted N-aryl rotation); the barriers to rotation were determined approximately at the coalescence temperature and in one case (1d) by complete line-shape analysis (CLSA). The dependence of the barrier to C,N rotation on the electron density polarization along the push-pull moiety (push-pull character) is discussed critically.

Anti-mosquito and antimicrobial nor-halimanoids, isocoumarins and an anilinoid from Tessmannia densiflora.

The nor-halimane diterpenoid tessmannic acid and its methyl, 2-methylisopropyl and 1-methylbutyl esters, the unusual isocoumarins 8-hydroxy-6-methoxy-3-pentylisocoumarin and 7-chloro-8-hydroxy-6-methoxy-3-pentylisocoumarin, and 5-pentyl-3-methoxy-N-butylaniline were isolated from the stem and root bark extracts of Tessmannia densiflora Harms (Caesalpiniaceae) that showed mosquito larvicidal activity. The structures were determined on interpretation of spectroscopic data. Tessmannic acid and its methyl ester exhibited antibacterial and antifungal activity. The compounds also caused high larvae and adult Anopheles gambiae mosquitoe mortality effects, and stronger mosquito repellency than that shown by the standard repellent DEET, hence indicating Tessmannia species to be potential sources of bioactive natural products.

Four isoflavones from the stem bark of erythrina sacleuxii

Abstract From the stem bark of Erythrina sacleuxii four new isoflavones were isolated and characterized as 5,7-dihydroxy-2′,4′,5′-trimethoxyisoflavone (trivial name, 7-demethylrobustigenin), 5,7-dihydroxy-4′-methoxy3′-(3-methylbut-2-enyl)isoflavone [3′-(3-methylbut-2-enyl)biochanin A], 5,7,3′-trihydroxy-4′-methoxy-5′-(3-methylbut-2-enyl)isoflavone [5′-(3-methylbut-2-enyl)pratensein] and 5,7,3′-trihydroxy-4′-methoxy-5′-formylisoflavone (5′-formylpratensein). The structures were determined on the basis of spectroscopic evidence.

Quinoxalines. Part 12: Synthesis and structural study of 1-(thiazol-2-yl)-1H-pyrazolo[3,4-b]quinoxalines—the dehydrogenative cyclization with hydroxylamine hydrochloride☆

Abstract Starting with 2-acetylquinoxaline a novel class of heterocyclic compounds, the 1-(thiazol-2-yl)-1H-pyrazolo[3,4-b]quinoxalines 4 , were prepared by following two different synthetic procedures: 2-acetylquinoxaline reacted with thiosemicarbazide to the thiosemicarbazones 1a which was (i) cyclized with α-halogeno ketones to the thiazoles 3 . These compounds were dehydrogenated in acidic medium to the title compounds 4 . (ii) The thiosemicarbazone 1a could be also dehydrogenated using NH2OH·HCl to the thioamide 5a and these, finally, were cyclized with α-halogeno ketones to the title compounds 4 . Only thiazole 3a was isolated, the other thiazoles 3 were dehydrogenated in a one-pot procedure. From the thioamide 5a also both the compounds 9 , by reacting with dibromodiacetyl, and 10 , by treatment with dimethyl acetylenedicarboxylate, were obtained. The analysis of both the 1H and 13C NMR spectra was not straightforward but could be attained finally by employing the whole arsenal of 1D and 2D NMR spectroscopy.

Quinoxalines XV. Convenient synthesis and structural study of pyrazolo[1,5-a]quinoxalines.

A series of aryloxymethylquinoxaline oximes, hitherto unknown and synthesized from the corresponding aldehydes, afforded in only one step pyrazolo[1,5-a]quinoxalines in the presence of acetic anhydride at high temperatures. A formal [3,5]-sigmatropic rearrangement was proposed as the mechanistic rationale for this unprecedented transformation. Saponification with potassium hydroxide furnished the free phenol derivatives which were studied by NMR spectroscopy and accompanying theoretical DFT calculations, establishing intramolecular hydrogen bonding and the spatial magnetic properties. Additionally, mass spectrometric fragmentation was investigated by B/E-linked scans and collision-induced dissociation experiments. The fragmentation pattern devoted a new gas phase rearrangement process, which proved to be unique and characteristic for pyrazolo[1,5-a]quinoxalines.

Synthesis and stereochemical studies of 1- and 2-phenyl-substituted 1,3-oxazino[4,3-a]isoquinoline derivatives

Abstract Starting from the 1′- or 2′-phenyl-substituted 1-(2′-hydroxyethyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline diastereomers 3 and 6 , 4-unsubstituted and 4-(p-nitrophenyl)- and 4-oxo-substituted 1-phenyl- and 2-phenyl-9,10-dimethoxy-2H,4H-1,6,7,11b-tetrahydro-1,3-oxazino[4,3-a]isoquinolines ( 7–12 ) were prepared. The relative configurations and the predominant conformations of the products were determined by NMR spectroscopy, by quantum chemical calculations and, for (2R∗,4S∗,11bR∗)-9,10-dimethoxy-4-(p-nitrophenyl)-2-phenyl-2H,4H-1,6,7,11b-tetrahydro-1,3-oxazino[4,3-a]isoquinoline ( 11 ), by X-ray diffraction.