Synthetic Studies Toward the Total Synthesis of Amphidinolide B1 PDF Download
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Author: Wei Zhang
Publisher:
ISBN:
Category : Antineoplastic agents
Languages : en
Pages : 660
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Author: Wei Zhang
Publisher:
ISBN:
Category : Antineoplastic agents
Languages : en
Pages : 660
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Author: Hugo M. Eng
Publisher:
ISBN:
Category :
Languages : en
Pages : 134
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Author: Liang Lu
Publisher:
ISBN:
Category : Marine natural products
Languages : en
Pages : 786
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The structural architecture present in marine toxin azaspiracid - 20 stereocenters, 9 rings, 3 separated spirocenters - has attracted considerable synthetic attention. Our efforts toward the synthesis of azaspiracid have led to the completion of both C1-C26 northern and C27-C40 southern halves. Herein, the synthesis of southern FGHI ring system is described. The key steps included an Andrus anti-aldol coupling to furnish the C32, C33 stereocenters, an acid-catalyzed ketalization to furnish FG rings, and a Yb(OTf)3-mediated spiroaminal formation to generate I ring. The first total synthesis of cytotoxic macrolides amphidinolide B1 and the proposed structure of amphidinolide B2 have been accomplished. The key developed protocols include a metal catalyst-free sequence for the synthesis of the diene subunit, a non-chelation-controlled aldol coupling to install the C18 stereocenter, an efficient macrocyclization of the 26-membered lactone ring, and the incorporation of the labile allylic epoxide moiety. The unique structure of the highly substituted diene functionality represents significant synthetic challenges. A Wittig / HWE reaction sequence yielded the C13-C15 diene moiety in good yield in excellent diastereoselectivity. Subsequent Sharpless epoxidation and Red-Al-mediated regionselective epoxide opening gave the C16 tertiary alcohol. The protecting groups on C21 were discovered to have significant effects on the aldol reaction between C9-C18 aldehyde and C19-C25 methyl ketone. Although chelating groups such as PMB, Bn afforded 18S isomer as a single diastereomer, the removal of these groups has proven problematic. Non-chelating silyl group generated 18R isomer in 8:1 dr at -100°C, while the 18S stereomer was obtained at -40°C in 1.2:1 dr. A spontaneous intramolecular Wadsworth-Emmons olefination established the 26-membered macrocycle. The oxidation and in situ elimination of a selenide moiety proceeded smoothly in the presence of free alcohols using TMSOOTMS. The first total synthesis of amphidinolide B1 and the proposed structure of amphidinolide B2 were accomplished in 29 linear steps. Additionally, We discovered that the initially proposed structure of amphidinolide B2 was incorrect.
Author: Brian J. Myers
Publisher:
ISBN:
Category :
Languages : en
Pages : 428
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Author: Peter Carew Sill
Publisher:
ISBN:
Category :
Languages : en
Pages : 450
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Author: Yang Su Tran
Publisher:
ISBN:
Category :
Languages : en
Pages : 192
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Author: Subham Mahapatra
Publisher:
ISBN:
Category : Macrolide antibiotics
Languages : en
Pages : 639
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More than 30 members of the diverse amphidinolide family of biologically active macrolides have been isolated over last three decades. From this family, amphidinolides C and F stand among the most complex and densely functionalized affiliates. Recently, we have accomplished the first total synthesis of amphidinolide F. The all-carbon framework of amphidinolide C has been synthesized. During endeavor toward the total syntheses of amphidinolides F / C, we have uncovered a "hidden symmetry element" present in the northern and southern domains of amphidinolides F / C. The southern C1-C and northern C1-C25 tetrahydrofuran segments were derived from a common intermediate. A scalable silver-catalyzed isomerization / cyclization on propargyl-benzoate / diol furnished the common intermediate in multigram quantity. The common intermediate provided access to over half of carbon backbone of the macrocycle as well as majority of stereochemistry present in amphidinolides F / C. Two strategically different techniques have been developed for the C9-C11 diene preparation. A metal-catalyst free Weinreb amide-vinyl lithium coupling / methylenation sequence furnished the diene motif. Alternately, diastereoselective addition of a dienyl iodide derived 2-lithio-1,3-diene species to an [alpha]-oxy aldehyde installed the C9-C11 diene and secured the C8 stereochemistry in single operation. The dienyl iodide was prepared via a regioselective hydrostannylation on an enyne. A challenging alkylation between an [alpha]-branched sulfone and an [alpha]-silyloxy iodide generated the all-carbon frameworks of amphidinolides F / C. An efficient oxidative desulfurization incorporated the carbonyl moiety at C15. The protecting group on C18 alcohol was found to have significant effect on the sulfone-iodide alkylation / oxidative desulfurization sequence. Installation of chelating ethoxyethyl ether on C18 alcohol helped the successful incorporation of C15 ketone and solved the deprotection problem in advanced stage of synthesis. A detailed analytical and computational study on proline sulfonamide-catalyzed aldol reactions has been performed. The pKa value of a proline sulfonamide catalyst was determined experimentally via NMR titration technique. Computational study revealed the origin of enhanced stereoselectivity by proline sulfonamide catalysts over parent proline. The non-classical hydrogen bonding interactions were found to be responsible for improved diastereoselectivity.
Author: Andrew Michael Lauer
Publisher:
ISBN:
Category :
Languages : en
Pages : 241
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Progress coupling of substrates, toward the total synthesis of amphidinolide B1 is described. The reductive 1,3-eynes and ketones was explored. It was found to work well with simple but failed to yield intermediates toward amphidinolide B1 [images] ... The coupling of 1,3-enyne and aldehyde fragments toward the synthesis of amphidinolides G3 and H4 is also described. The entire carbon skeleton of these natural products has been prepared from this coupling and a subsequent installation of a methyl group using an indium based reagent ... [images].
Author: Stuart Edward Bradley
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Hugo M. Eng
Publisher:
ISBN:
Category :
Languages : en
Pages : 240
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