Über Pterinchemie 76. Mitteilung [1] Eine einfache Synthese von Leucovorin

A Convenient Synthesis of Leucovorin The synthesis of leucovorin, a 5-formyl-(6R or S)-5,6,7,8-tetrahydropteroyl-L -glutamic acid (II) is described. The L -folic acid was first reduced to (6R, S)-tetrahy-dro-L -folic acid (I); formylation with methyl-formate in DMSO gave directly leucovorin (as a diastereomeric mixture) in good yields. To demonstrate, that the formylation occurred regiospecifically at N (5) and not at N (10), N (10)-nitroso-(6 R, S)-tetrahydro-L -folic acid was formylated under the same conditions. Reductive elimination of the N (10)-nitrosogroup gave the identical leucovorin as in the previous case. The synthetic leucovorin was biologically as active as the natural product with Streptococcus faecalis ATCC 8043 and Pediococcus cerevisiae ATCC 8081.     

5,6,7,8-Tetrahydro-4H-1,2,5-oxadiazocin-6-one durch Ringerweiterung nach Addition eines 3-Isoxazolidinons mit 3-Amino-2H-azirinen

5,6,7,8-Tetrahydro-4H-1,2,5-oxadiazocin-6-ones, Ring Enlargement Products from a 3-Isoxazolidinone and 3-Amino-2H-azirines 3-Dimethylamino-2H-azirines 1 and 4,4-dimethyl-3-isoxazolidinone ( 7 ) undergo already at room temperature a ring enlargement reaction to yield 5,6,7,8-tetrahydro-4H-1,2,5-oxadiazocines of type 8 . The structure of 8a has been confirmed by X-ray crystallography. The conformation of the eight-membered ring with a trans-amide group is of particular interest (Fig. 1 and 2).     

On the regularity of minimal surfaces with free boundaries in Riemannian manifolds

We show c^1,-regularity of minimal surfaces in Riemannian manifolds with a free boundary on C²-hypersurfaces with bounded second fundamental form and a uniform neighborhood on which the nearest point projection is uniquely defined and differentiable. The decisive step is the proof of continuity at the free boundary.partially supported by SFB 72 (Deutsche Forschungsgemeinschaft)     

Cyano-modified pre-coated plates — a medium polar modification for high performance thin-layer chromatography

Summary The introduction of a cyano-modified, pre-coated layer substantially widens the selectivity of stationary phases in thin-layer chromatography. This is a moderately polar sorbent based on silica gel 60, which can be used both in adsorption chromatography and in reversed-phase chromatography. This new pre-coated layer is particularly suitable for separation of steroids, alkaloids and derivatized amino acids. The possibility of separating habitforming drugs and preservatives in the presence of ionpair reagents is also discussed.     

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Ohne Zusammenfassung     

Comparison theorems and hypersurfaces

We compare the second fundamental forms of a family of parallel hypersurfaces in different Riemannian manifolds. This leads to new proofs for the distance and volume comparison theorems in Riemannian geometry. In particular, we get a new result on the volume of the set of points with distancer from a totally geodesic submanifold, for any r. The analytic prerequisite is the investigation of the Riccati type ODE which is satisfied by the second fundamental form of a parallel hypersurface family.Supported by DFG     

Simultaneous determination of aluminoxamine and ferrioxamine in post-hemodialysis fluids by spectrophotometry and multivariate calibration

A spectrophotometric method for simultaneous determination of Al(III) and Fe(III) using the chelator Desferal® (desferrioxamine B) was developed. Partial least squares (PLS) regression was performed to resolve the overlapped signals obtained from Al(III) and Fe(III) complexes. The parameters controlling behavior of the system were investigated and optimum conditions were selected. PLS was the choice for the analysis of binary mixtures of Fe(III) and Al(III) over the range of 0.1 to 0.8 mg L^?1 by using the data of first derivative spectra. Absorbance data were taken between 200 and 600 nm. The calculated sensitivity values for the multivariate method were 4.88 and 5.64 for Al(III) and Fe(III), respectively. Multivariate detection limits were 0.075 and 0.064 mg L^?1 for Al(III) and Fe(III), respectively. The method was applied to real post-hemodialysis samples, and sample digestion by UV irradiation was discussed.