Synthesen der Nonactinsäure

Abstract

1x 74)Sumnzury. Two stercosclcctivc syntheses o f n o n x t i c acid I, the buildmg block of the niacrotetrolide antibiotic nonactin are described. The characteristic cis-configuration of the 2,s-substltuents on the tctrahydrofuran ring of I is obtained in the first synthcsis by catalytic hydrogenation of the furan derivative X. This key intermediate possesses thc carbon skeleton and correct distribution of oxygen functions for convcrsion into nonactic acid. It is synthesized by a n electrophilic substitution of 2-acctonylfuran (VI) with the N-cyclohexyl-N-propcnyl nitrosonium ion (V) generated from the corresponding cr-chloronitrone (VII) and silver fluoroborate, followed by hydrolysis and oxidation of the aldchydc group.Thc sccond synthesis starts with a tliol already having the correct configuration of the side chain that contains the hydroxyl group. For this purpose threo-l-octcn-5,7-diol (XV) is synthesized from acetylacetonc in two steps. Oxidative cleavngc of the tcrminal double bond of this thveo-diol yields a n aldehyde which is converted by a Wittig reaction, with the carbanion, obtained froin clicthyl u-methoxycarbonylethyl phosphonatc, into thc o p i chain intermediate, 2-methy1-6,8dihydroxy-2-nonenoic acid methylester (XV t 1 I). Base-catalyzed cyclisation of this M , B-unsaturatcd dihydroxy cstcr yields thc methyl ester of nonactic acid (I) as the main product.

Furan fatty acids: Occurrence, synthesis, and reactions. Are furan fatty acids responsible for the cardioprotective effects of a fish diet?

“…Similar isolation methods are applied to obtain F-acids from mammalian tissue (61). To avoid the time-consuming separation by urea precipitation, enrichment of F-acid methyl esters can be achieved by hydrogenation of the furan rings with a rhodium catalyst on alumina (67) to THF derivatives (54). The latter can easily be separated from saturated and unsaturated FAME owing to their high polarity.…”

Chemo-, Regio-, and Stereoselective Cyclization of 1,3-Bis(trimethylsilyloxy)-1,3-butadienes with Functionalized Epoxides

“…1997, 243, 274 ± 282. [12] Mass spectra were recorded on a Micromass Quattro II mass spectrometer (Micromass, Manchester, UK) fitted with a Z-Spray electrospray source. NH 4 OAc (2.5 mm, pH 7.0 unless otherwise stated) was used as a spraying buffer at a flow rate of 5 mL min -1 .…”

“…1999, 274, 30 950 ± 30 956. [14] The BmPBP solution [12] was incubated with a 50-fold molar excess of each ligand overnight at 4 8C. Alcohols were added to buffered BmPBP as 0.6 m ethanolic solutions.…”

Synthese der Phoracantholide K, O und M

“…Laboratorium f i r Organische Chemie der Eidgenossischen Technischen Hochschule Zurich, Synthesis of Phoracantholide K, 0 and M Summary Two 14membered ring lactones 3 and 4 and a 12membered ring lactone 5 isolated from the metasternal secretion of the eucalypt longicorn Phoracantha synonymu have been synthesized as racemic mixtures by the following method. Reaction of the dilithium derivative of 5-hexynoic acid (6) with threo-8-bromo-2,4-isopropylidenedioxyoctane (7), followed by removal of the protecting group and esterification with diazomethane gave methyl-threo-1 1 ,13-dihydroxy-S-tetradecynoate (8) (s. Scheme 2). Partial hydrogenation of the triple bond in 8 with Lindlar Pd-catalyst, followed by saponification lead to (threo,Z)-ll, 13-dihydroxy-5-tetradecenoic acid (10).…”