Albrecht Lieberknecht

Total synthesis of of4949-III, a natural inhibitor of aminopeptidase B from ehrlich ascites carcinoma cells

Abstract The total synthesis of the cyclopeptide OF4949-III 1c is described. Key steps are two preparations of didehydroamino acid moieties by condensations of aldehydes and phosphorylglycine esters and two homogeneous hydrogenations with more than 98% ee and de, respectively, to give derivatives of isodityrosine 8a,b . The peptide ring is constructed by the cyclization of an (ω-aminopentafluorophenyl ester in a two phase system in 40% yield.

What is the structure of barettin? Novel synthesis of unsaturated diketopiperazines

Abstract Several unsaturated diketopiperazines 1a - 1f as well as a compound with the proposed structure 2 of barettin were synthesized by a new method via esters of diketopiperazine phosphonic acid. The proposed structure of barettin was found to be incorrect.

Nitrile oxide cycloadditions to olefinated sugars

Carbohydrate derivatives with a spiro-isoxazoline moiety as present in psammaplysins and ceratinamides (metabolites isolated from marine sponges) were prepared in good yields and excellent regio- and diastereoselectivity by a route involving Wittig olefination and 1,3-dipolar cycloaddition as key steps.

The total synthesis of frangulanine

The reported preparation of the p-ansa compound frangulanine, previously isolated from Rhamnus frangula L., also constitutes the first total synthesis of a fourteen-membered cyclopeptide alkaloid.

Aminosäuren und peptide - XXXXII. Synthese von Chlamydocin + epi-Chlamydocin

Abstract The total synthesis of the cytostatic Chlamydocin together with his diastereomer epi-Chlamydocin is described.

Total synthesis of tetraacetyl clionamide

Abstract Tetraacetyl clionamide, a 6-bromotryptophan derivative from the sponge Cliona celata was synthesized from gallic acid.

Stereoselective synthesis of olefinated sugars

Abstract The stereoselective synthesis of olefinated sugars at the anomeric center via Wittig reaction of α,β- glycosyl phosphonium tetrafluoroborates, easily prepared from α,β- methoxy glycosides, is described.

Diastereoselective synthesis of ribofuranosyl glycines

Abstract The diastereoselective synthesis of β-C-ribofuranosyl glycines by condensation of ribofuranoses and phosphoryl glycinesters1 in a one-pot procedure is described.

Stereoselective glycosidations of olefinated sugars

Abstract The glycosidation of olefinated sugars using a catalytic amount of boron trichloride or triphenylphosphine hydrobromide proceeded in a highly stereoselective fashion to give the α anomers with good to high yields. The use of camphorsulphonic acid also afforded high stereoselectivity but lower yields were obtained.

Diastereoselective synthesis of β-(3,4,6-tri-O-benzyl-2-deoxy-β-D-galactopyranosyl)-N-tert-butoxycarbonyl-D-alanine

Abstract Key steps in the synthesis of β -(3,4,6-tri- O -benzyl-2-deoxy-β-D-galactopyranosyl)- N - tert -butoxy-carbonyl-D-alanine are the Wittig reaction of 2-deoxy-galactopyranosylphosphonium salt 2 and Garner aldehyde, as well as the subsequent diastereoselective hydrogenation of the olefinated sugar 3a,b .