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 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 ).     

Pterobiline and neopterobilines, reactivity and structures (author's transl)]

Pterobiline and neopterobilines, reactivity and structures Pterobiline (biliverdine IX γ) and the two neopterobilines: phorcabiline and sarpedobiline, are the three main bile pigments found in Lepidopters. Studies on the reactivity of pterobiline ( 1 ) and phorcabiline esters are reported. Preparation of derivatives, in vitro transformation of pterobiline into phorcabiline, analysis of the pigments and their derivatives by field desorption mass spectrometry and Fourier transform NMR., lead to the structure 5 for the dimethyl ester of phorcabiline. By a similar reaction, biliverdine IX δ ( 15 ) affords the neobiliverdine IX δ ( 16 ). Possibility of an easy formation of new tetrapyrrolic compounds in the IX γ and IX δ series is thus reported for the first time.     

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.