Holger Hartenstein

(2R)-2-β-D-glucopyranosyloxy-4-hydroxy-2H-1,4-benzoxazin-3(4H)-one from Secale cereale

Abstract (2 R )-2-β- d -Glucopyranosyloxy-4-hydroxy-2H-1,4-benzoxazin-3(4H)-one was isolated from Secale cereale for the first time as a pure substance. The absolute configuration was determined as the 2 R -type by spectroscopic methods.

α-Hydroxylation of cyclic hydroxamic acids by peroxide oxidation : A novel approach to allelochemicals from Gramineae

Abstract Naturally occurring hemiacetals DIBOA and DIMBOA were synthesized by the first α-hydroxylation of N-hydroxylactams via m-chloroperbenzoic acid oxidation of corresponding cyclosilyl enol ethers.

Separation of enantiomers and diastereomers of 4-hydroxy-2H-1,4-benzoxazin-3(4H)-one derivatives by capillary electrophoresis

SummaryA high performance capillary electrophoresis (HPCE) procedure for the enantioseparation of the methyl acetals3 and4 of the natural products DIBOA1 and DIMBOA2, respectively, has been developed using borate buffers (pH 9–10 range), cyclodextrins as chiral additives and addition of up to 20% methanol. A mixture of GDIBOA5 and GDIMBOA6 of natural origin was also clearly separated. HPCE proved to be superior to HPLC by the first separation of GDIBOA5 and three of its diastereomers resulting from a synthetic approach to this acetalglucoside.

Diastereoselective syntheses of 2-β-d-glucopyranosyloxy-2H-1,4-benzoxazin-3(4H)-ones from gramineae

Abstract The first diastereoselective syntheses of the natural acetal glucosides, (2R)-2-β- d -glucopyranosyloxy-4-hydroxy -2H-1,4- benzoxazin -3(4H)- one and (2R)-2-β- d -glucopyranosyloxy-7-methoxy -2H-1,4- benzoxazin -3(4H)- one , are described by reaction of O-(2,3,4,6- tetra -O- acetyl-β- d -glucopyranosyl ) trichloroacetimidate with hemiacetalic aglucones of the 2-hydroxy-2H-1,4-benzoxazin-3(4H)-one skeleton.

Electrochemical reduction of o-nitrophenylthioacetic derivatives. Production of 2H-1,4-benzothiazines

Comparative studies of the electrochemical reduction of 2-(o-nitrophenylthio)-acetic acid and its methyl ester in aqueous media of different acidity show that reduction of the ester in an ammoniacal buffer is the best adapted for electrosynthesis of 4-hydroxy-2H-1,4-benzothiazin-3(4H)-one. The electrochemical behaviours of the corresponding phenylhydroxylamines and azoxy compounds are also investigated.