No abstract

A convenient and practical multi‐gram procedure for the synthesis of second‐ (G2; 4a, 5a, 5d) and third‐generation (G3; 6a) dendrons with orthogonally protected functional groups in the periphery (hydroxy) and at the focal point (carboxylic acid) is described. It uses the amply available first‐generation dendrons with amine and carboxylic ester functions (1) and tetrahydropyranyl‐protected hydroxy and carboxylic acid functions (2b, 3), respectively, which are connected via amides by peptide methods. Purification is either done by recrystallization or simple filtration through silica gel and yields the products as analytically pure materials on a several‐gram scale (even for G3). ‘The dendrons’ protective groups are proven to be orthogonal (500‐MHz NMR) which makes them useful components (building blocks) of a future dendron construction kit for a versatile synthesis of, for example, dendronized polymers.

Mushrooms of the genus Retiboletus contain the retipolides A–D (1, 6–8), unusual 14‐membered spiromacrolides with a biphenyl ether linkage. The structures of these metabolites suggested a biogenetic sequence starting from retipolide E (16), which could furnish the unique 2(3H)‐oxepinone unit of retipolide C (7) via an oxidative enlargement of the 4‐hydroxyphenyl ring. A subsequent O/C‐acyl shift would then lead to the cyclopenta[c]pyran system of retipolide A (1). The proposed precursor 16 was synthesized and subsequently detected in the fungal extract in addition to the probable biosynthetic intermediates butyrolactone II (13), tyrosol (14), and secoretipolide E (15). The structural elucidation of retipolide A (1) was accomplished after transformation into a methoxyfulvene derivative 2a, and the absolute (R) configuration of 1 was assigned by a single‐crystal X‐ray analysis of the corresponding (S)‐sec‐butoxyfulvene analogue 2b. Some samples of R. retipes/ornatipes contained isoretipolide A (9), an isomer of 1 with a highly strained 12‐membered lactone ring incorporating two C,C‐coupled 4‐hydroxyphenyl units. A comparison of the CD spectrum of retipolide A (1) with those of the other retipolides and isoretipolide A (9) indicates that all of these macrolides possess R configuration. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Other natural products U 0800Retipolides -Unusual Spiromacrolactones from the Mushrooms Retiboletus retipes and R. ornatipes. -The structural elucidation of a biosynthetically and structurally unique set of fungal metabolites named retipolides A (Ia)-E (III) is reported. -(JUSTUS, K.; HERRMANN, R.; KLAMANN, J.-D.; GRUBER, G.; HELLWIG, V.; INGERL, A.; POLBORN, K.; STEFFAN, B.; STEGLICH*, W.; Eur.

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