59 research outputs found
Synthesis of the C1 to C13 tetrahydropyranyl-resorcylate core of paecilomycin B
A d-Glucose derived tetrahydropyran was converted into the C1 to C13 tetrahydropyranyl-resorcylate core of paecilomycin B in seven steps. Key transformations included the synthesis of a diketo-ester dioxinone, which upon thermolysis underwent a retro-hetero-Diels-Alder fragmentation to generate an acyl ketene. This was subsequently trapped by a secondary alcohol affording a triketo-ester, which was efficiently aromatized to produce the advanced resorcylate intermediate
Biomimetic syntheses of analogs of hongoquercin A and B by late-stage derivatization
The hongoquercins are tetracyclic meroterpenoid natural products with the transātransoid decalin-dihydrobenzopyran ring system, which display a range of different bioactivities. In this study, the syntheses of a range of hongoquercins using gold-catalyzed enyne cyclization reactions and further derivatization are described. The parent enyne resorcylate precursors were synthesized biomimetically from the corresponding dioxinone keto ester via regioselective acylation, Tsuji-Trost allylic decarboxylative rearrangement, and aromatization. The dioxinone keto ester 12 was prepared in 6 steps from geraniol using allylic functionalization and alkyne synthesis
Pyrimidine nucleosides syntheses by late-stage base heterocyclization reactions
An efficient two-step procedure for the syntheses of pyrimidine nucleosides is presented. A series of glycosyl 5-(aminomethylene)-1,3-dioxane-4,6-dione derivatives were prepared from Ī²-anomeric isonitriles by reaction with Meldrumās acid or by allowing aminomethylene Meldrumās acid to react with an 1-aldofuranosyl halide or acetate. The resultant 5-(aminomethylene)-1,3-dioxane-4,6-dione derivatives underwent reaction with benzyl- or 2,4-dimethoxybenzyl isocyanate via transacylation to provide uridine-5-carboxylic acid derivatives and related nucleosides. These nucleoside carboxylic acids were converted into other C-5 derivatives by bromo-decarboxylation with N-bromosuccinimide
Anaerobic animals from an ancient, anoxic ecological niche
Tiny marine animals that complete their life cycle in the total absence of light and oxygen are reported by Roberto Danovaro and colleagues in this issue of BMC Biology. These fascinating animals are new members of the phylum Loricifera and possess mitochondria that in electron micrographs look very much like hydrogenosomes, the H2-producing mitochondria found among several unicellular eukaryotic lineages. The discovery of metazoan life in a permanently anoxic and sulphidic environment provides a glimpse of what a good part of Earth's past ecology might have been like in 'Canfield oceans', before the rise of deep marine oxygen levels and the appearance of the first large animals in the fossil record roughly 550-600 million years ago. The findings underscore the evolutionary significance of anaerobic deep sea environments and the anaerobic lifestyle among mitochondrion-bearing cells. They also testify that a fuller understanding of eukaryotic and metazoan evolution will come from the study of modern anoxic and hypoxic habitats
Four-directional synthesis of adamantane derivatives
1-Adamantanemethanol, 1,3-adamantanedimethanol and 1,3,5,7-adamantanetetramethanol were converted into adamantanes functionalized with one or four (2R,1S)-2-formyl-1-cyclopropyl residues using Charette enantioselective cyclopropanation reactions and with one, two or four 4-ethoxy- (or 4-t-butoxy)-3-diazo-2,4- dioxobutyl residues from aldehyde and diazo-acetate ester condensation reactions by 1-directional, 2- directional or 4-directional syntheses. The synthesis of adamantane fused to cyclopentadiene is also reported
Sequential Ketene Generation from Dioxane-4,6-dione-keto-dioxinones for the Synthesis of Terpenoid Resorcylates
Trapping
of the ketene generated from the thermolysis of 2-methyl-2-phenyl-1,3-dioxane-4,6-dione-keto-dioxinone
at 50 Ā°C with primary, secondary, or tertiary alcohols gave the
corresponding dioxinone Ī²-keto-esters in good yield under neutral
conditions. These intermediates were converted by palladium(0)-catalyzed
decarboxylative allyl migration and aromatization into the corresponding
Ī²-resorcylates. These transformations were applied to the syntheses
of the natural products (Ā±)-cannabiorciĀchromenic and (Ā±)-dauriĀchromenic
acid
Meroterpenoid total synthesis: conversion of geraniol and farnesol into amorphastilbol, grifolin and grifolic acid by dioxinone-Ī²-keto-acylation, palladium catalyzed decarboxylative allylic rearrangement and aromatization
Biomimetic total syntheses of resorcinols amorphastilbol, grifolin and grifolic acid have been completed in four steps starting from geraniol and farnesol without the use of phenolic protection. The key steps involve C-acylation of dioxinone-Ī²-keto esters, followed by palladium catalyzed decarboxylative allylic rearrangement and biomimetic aromatization
Biosynthetic Study of FR-900848: Origin of the Aminodeoxynucleoside Part
Biosynthetic studies of the antifungal agent, FR-900848, were undertaken by feeding experiments with D-[U-13C6]glucose, L-[4-13C]aspartate, [5,5-2H2]dihydrouridine and [5,5-2H2]dihydrouracil. The 5Ā“Ā“-amino-5Ā“Ā“-deoxy-5Ā“,6Ā“-dihydrouridine moiety was derived from ribose and aspartate. Based on the feeding experiments, a detailed biosynthetic pathway producing the aminodeoxydihydrouridine moiety of FR-900848 was proposed
- ā¦