Synthesis and absolute configuration of the enantiomers of verapamil (author's transl)]

Synthesis and Absolute Confifguration of the Enantiomers of Verapamil. Starting from the acids IV-(+) and IV-(?), a synthesis of the enantiomers I-(+) and I-(?) of the coronary vasodilator Verapamil is described and their absolute configuration determined through a chemical filiation with the acid XII-(S)-(+).     

Synthesis of nonactin (author's transl)]

Synthesis of Nonactin. The macrotetrolide antibiotic nonactin (I), containing four units of a C₁₀ hydroxy acid, has been synthesized starting from two adequately protected derivatives (III and IV) of nonactic acid (II). The 32-membered ring of the macrotetrolide is built up by a sequence of condensation and deprotection steps leading first to a product with two, and subsequently to one with four nonactic acid residues (VIII) which is then cyclized in the presence of Ag⁺-ions. Two reactions forming ester bonds have been developed to condense the hydroxy acids and to effect the final cyclization. In one the activation of the carboxyl group is achieved by conversion into the mixed anhydride with 2,4,6-trimethylbenzene sulfonyl chloride in pyridine. In the other the Ag⁺-ion induced reaction of a S-(2-pyridyl) hydroxy carbothioate is used to form the corresponding macrocyclic lactone. In the case of nonactin the ring closure is promoted by the coordinating effect of Ag⁺-ions present in the reaction mixture.     

Synthesis of racemic proferrorosamin and ferrorosamin A (author's transl)]

Synthesis of Racemic Proferrorosamin and Ferrorosamin A. The synthesis of proferrorosamin starting from methyl 2-phenylacetamido-acrylate and ethyl 3-oxo-3-(2-pyridyl)-propionate is described. Proferrorosamin A is complexed with Fe²⁺ and isolated as pure ferrorosamin A.     

Synthesis of a homologous 3beta-hydroxycard-5,22-dienolide (author's transl)]

Synthesis of a homologous 3β-hydroxycard-5,22-dienolide. We describe the synthesis of 4′-[(3β-hydroxy-androst-5-en-17β-yl)methyl]-2′(5′)-furanone ( 22 ) starting from 3β-acetoxy-androst-5-ene-17β-carboxylic acid ( 5 ).     

Synthesis of eupomatilone-6 and assignment of its absolute configuration

[Reaction: see text]. The Zn-mediated Barbier reaction of the biarylaldehyde 8 with crotyl bromide followed by hydroboration and oxidation provided the gamma-butyrolactones 4 and 5. The stereoselective installation of methyl group at C-3 by using LiHMDS and MeI completed the synthesis of racemic eupomatilone-6 (2) and its diastereomer 3. The spectroscopic data of 2 was in full agreement with reported spectra of natural product, thus confirming the revised relative configuration of eupomatilone-6. Similarly, an optically active (3R,4R,5S)-isomer of eupomatilone-6 (23) was prepared in which the aldol reaction with thiazolidinethione as a chiral auxiliary was employed as a key step. On the basis of the spectroscopic data and optical rotation values of 23, the absolute configuration of eupomatilone-6 was proposed.     

Determination of vitamin D3 and its isomers in D3 resins and in mixtures with vitamin A acetate (author's transl)]

Vitamin D3 and its isomers, prepared from 7-dehydrocholesterol by photochemical reaction, can be separated and quantitatively determined by high-pressure liquid chromatography on aluminium oxide using chloroform as the eluting agent. The determination of small amounts of vitamin D3 in an excess of vitamin A acetate can be achieved by the same method.     

Synthesis of alkyl-5H-cyclopenta[b]pyrazines (author's transl)]

Synthesis of alkyl-5H-cyclopenta[b]pyrazines. Alkyl-5H-cyclopenta[b]-pyrazines (sometimes together with 5-alkylidene-5H-6,7-dihydrocyclopenta[b]pyrazines) are prepared by thermal degradation of 5-acetoxy-5H-6,7-dihydrocyclopenta[b]pyrazines; these are obtained by treatment of alkyl-5H-6,7-dihydrocyclopenta[b]pyrazine N-oxides with acetic anhydride. Cyclopenta[b]pyrazines which are potentially present in roasted food flavors possess interesting organoleptic properties.     

Synthesis of enantiomerically pure desmethylzopiclone and determination of its absolute configuration

Two synthetic methods have been established for the preparation of enantiomerically pure desmethylzopiclone, a metabolite of zopiclone. In Method A, (S)-desmethylzopiclone was prepared by demethylation of (S)-zopiclone with 1-chloroethyl chloroformate in high yield. Enantiomerically pure zopiclone (>99% ee) was obtained through a highly efficient resolution process in >36% overall yield. In Method B, racemic desmethylzopiclone was resolved with l-N-benzyloxycarbonyl phenylalanine (l-ZPA) followed by recrystallization in good yield. The absolute stereochemistry of the (+)-enantiomer was first determined to be the (S)-configuration by X-ray crystallography.     

Synthesis and absolute configuration of (−)-serantrypinone

A synthesis of (−)-serantrypinone (3) has been achieved from l-tryptophan. A key reaction involves the transformation of a selenoxide to an acetate via trapping of a presumed intermediate in a seleno-Pummerer reaction.     

The synthesis of 2,2'-Dinor-carotenoids (author's transl)]

The Synthesis of 2,2′-Dinor-carotenoids. 2,2′-Dinor-carotenoids which include the naturally occurring actinioerythrol ( 1 ) and the blue carotenoid violerythrin ( 2 ) have been obtained by total synthesis. The synthesis starts with acetone and acetylene and yields compounds 1 and 2 as well as other carotenoids of the same type.     

Synthesis and absolute configuration of annuionone A

Synthesis of both enantiomers of annuionone A (1), an allelopathic agent isolated from Helianthus annuus (sunflower), was accomplished. The absolute configuration of the naturally occurring 1 was determined to be 1S,5R,8R.