Naphthalene Disaccharide Fragments as Building Blocks for Angucycline Synthesis

Krohn, Karsten; Bäuerlein, Christiane

doi:10.1080/07328309908544037

Cited by 4 publications

(3 citation statements)

References 18 publications

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“…We now disclose two routes to the first total synthesis of the disaccharide, antibiotic 100-1 (3), based on the earlier model studies on the stereoselective disaccharide deoxysugar synthesis performed on naphthol models [23] and on the tetrangomycin synthesis that relied on a Diels-Alder reaction to construct the benzo[a]anthraquinone skeleton. [24] A direct electrophilic substitution of potential C-glycosyl donors with the electrondeficient naphthoquinones is not possible.…”

Section: Introductionmentioning

confidence: 99%

“…In the previous model studies, we employed scandium triflate for the first time in an a-selective O-glycoside synthesis. [23] According to that procedure, the alcohol 15 was treated with the L-rhodinal benzoate (16) [23] and scandium triflate to yield the a-O-gylcoside 17 selectively in 72% yield at 70% conversion as a yellow resin in addition to recovered starting C-glycoside 15. Zemplén deacylation using sodium methoxide in methanol then afforded the deprotected disaccharide 18.…”

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confidence: 99%

“…The stage was now set to perform the selective disaccharide synthesis making use of the experience gained in our previous model studies with the bicyclic naphthol derivatives. [23] We applied a very easy and high yielding three step protection strategy. First, the slightly less hindered 3-OH of the olivose residue in 12 was selectively protected as the TBDMS ether 13, as also performed by Suzuki et al in the synthesis of antibiotic C-104.…”

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Total Synthesis of Angucyclines. XVII. First Synthesis of Antibiotic 100‐1, a Deoxydisaccharide Angucycline Antibiotic of the Urdamycinone B‐Type

Krohn

Agócs

Bäuerlein

2003

Journal of Carbohydrate Chemistry

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Two routes to the deoxydisaccharide angucycline antibiotic 100-1 (3) are described. Key steps comprise the regioselective oxidation/bromination of the 1,5-diacetoxyolivose C-saccharide 7 to the bromoquinone 8. Diels -Alder reaction of the bromoquinone with the diene 9 followed by HBr elimination afforded the urdamycinone B precursor 11 as a diastereomeric mixture. Selective protection as the TBDMS ether 13, acetylation and deprotection of the silyl ether afforded the alcohol 15 which was selectively glycosylated to the a-rhamnal glycoside 17 in 72% yield (at 70% conversion) using benzoyl rhamnal (16) as the glycoside donor and scandium triflate as the promotor. The silyl group at C-3 of the aglycone was then transformed into a hydroxyl group. Zemplén deacylation and photooxidation of the benzylic position at C-1 then converted the two diastereoisomers into the natural product 3 and the C-3 diastereoisomer 20. At this stage the diastereomers 3 and 20 were separated. Alternatively and more easily, the diastereomers were separated at the stage of the urdamycinone B analogues 21a and 21b, followed by a similar reaction sequence to the natural disaccharide 3.

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Section: Introductionmentioning

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Total Synthesis of Angucyclines. XVII. First Synthesis of Antibiotic 100‐1, a Deoxydisaccharide Angucycline Antibiotic of the Urdamycinone B‐Type

Krohn

Agócs

Bäuerlein

2003

Journal of Carbohydrate Chemistry

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Transformation of Glycals into 2,3‐Unsaturated Glycosyl Derivatives

Ferrier

Zubkov

2003

Organic Reactions

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Various elimination procedures conducted on appropriate pyranoid and furanoid carbohydrate derivatives, especially on O ‐protected glycosyl halides afford cyclic vinyl ethers which Fischer (inappropriately) named glycals. These are used extensively in general organic synthesis and for the preparation of non‐carbohydrate natural products as well as biologically important complex carbohydrates and glycoconjugates. The best known member, tri‐ O ‐acetyl‐D‐glucal, is normally made from tetra‐ O ‐acetyl‐alpha‐D‐glucopyranosyl bromide, is commercially available, and is used very frequently in this chapter to represent the family in examples of the reactions under discussion. Because of the pronounced region‐ and stereoselectivities with which their addition reactions can be conducted, glycal derivatives are of major importance in synthesis. They also, however, take part in rearrangement processes that, likewise, have proved useful for synthesis. The principal one involves nucleophilic substitution of the allylic group with allylic rearrangement and results in products having double bonds in the 2, 3 positions and new substituents at the anomeric centers. By far the simplest and most commonly used way to this conversion involves the removal of the allylic substituent of the glycal and the generation of highly resonance‐stabilized oxocarbenium ion intermediate. This may then react with nucleophiles at the anomeric center to give products as mixtures of diastereomers. Many examples and variations of this theme are described and form the major part of this chapter, but other ways are also considered Almost no formal mechanistic studies have been carried out on the reactions in this chapter. Categorization of mechanism required for the treatment of this topic has been done on the basis of conditions used, product identification and largely, chemical intuition.

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