René Thürmer

Stereoselective Solid-Phase Synthesis of β-Lactams-A Novel Cyclization/Cleavage Step towards 1-Oxacephams.

Despite the antibiotic activity and the attractiveness of β-lactams, the solid-phase synthesis of this class of compounds has been barely reported. Now the diastereoselective synthesis of the 1-oxacepham 2 from the resin-bound β-lactam derivative 1 has been achieved in five steps. The synthesis of 2 and other 1-oxacephams is attractive because all the reaction steps proceed in high yield, the purity of the product is high, and the reaction sequence is simple.

Synthesis of a 1-oxacephem structurally related to clavulanic acid from D-glucuronolactone

Abstract [2+2]Cycloaddition of chlorosulfonyl isocyanate to 3-O-vinyl ethers derived from D-glucose and D-glucuronolactone proceeded with an excellent stereoselectivity to provide azetidin-2-ones with (R) configuration at C-4′. Intramolecular N-alkylation afforded 1-oxabicyclic-β-lactams having six- or seven-membered ring fused to the four-membered one.

A useful regioselective approach to episulfides via cis-oriented anhydro triflate sugars

An efficient method for the regioselective synthesis of episulfides, showing remarkable proteinase-inhibiting activity, from cis-oriented anhydro triflate sugars is decribed.

Stereochemical model of [2+2]cycloaddition of chlorosulfonyl isocyanate to chiral vinyl ethers

A comparison of steady-state NOE coefficients measured for vinyl-substituted isopropyl ethers with conformations generated by a molecular mechanics program allowed a characterization of the most favorable ground state conformations. With high confidence it was possible to assign the lowest energy conformation to one which is characterized by a diastereo-zeroplane consisting of the s-trans vinyl group, the stereogenic center and the methyl group (Fig. 3). A stereochemical model of the transition state for [2+2]cycloaddition of chlorosulfonyl isocyanate and vinyl ethers is proposed, based on the lowest energy conformation derived from NOE coefficients, which agrees well with the experimental facts and provides a sound explanation of the direction of asymmetric induction.

NEIGHBOURING GROUP PARTICIPATION OF C-6 SUBSTITUENTS OF GLUCOSE DERIVATIVES ON THE STEREOSELECTIVITY OF THE N-GLYCOSIDIC LINKAGE OF GLYCOPEPTIDES

The first example of a glycopeptide with a direct N-α-glycosidic linkage between the trisaccharide and the amino acid residue was found in the glomerular basement membrane of rats. In connection with the total synthesis of nephritogenoside, glycosyl azides with different protecting groups and carbohydrate chain lengths are synthesized, reduced to the corresponding glycosyl amines and coupled with Z-Asp-OBzl. Remarkable differences in the α:β ratio of the condensation products are observed, caused by neighbouring group participation.