- Enantioselective Total Synthesis of Didesepoxyrhizoxin
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The first synthesis of the antitumor macrolide didesepoxyrhizoxin is described.
- Kende, Andrew S.,Blass, Benjamin E.,Henry, James R.
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- Total synthesis of the marine toxin phorboxazole A using palladium(ii)-mediated intramolecular alkoxycarbonylation for tetrahydropyran synthesis
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The potent antitumor agent phorboxazole A was synthesized from six subunits comprising C1-C2 (115), C3-C8 (98), C9-C19 (74), C20-C32 (52), C33-C41 (84) and C42-C46 (85). Tetrahydropyrans B and C containing cis-2,6-disubstitution were fabricated via palladium(ii)-mediated intramolecular alkoxycarbonylation which, in the case of tetrahydropyran C, was carried out with catalytic palladium(ii) and p-benzoquinone as the stoichiometric re-oxidant. Tetrahydropyran D was obtained by a stereoselective tin(iv)-catalyzed coupling of a C9 aldehyde with an allylsilane, and the C19-C20 connection was made using a completely stereoselective Wittig-Schlosser (E) olefination. Coupling of the oxazole C32 methyl substituent with the intact C33-C46 δ-lactone 3 was accompanied by elimination of the vinyl bromide to a terminal alkyne, but the C32-C33 linkage was implemented successfully with 83 and C33-C41 lactone 84. The C42-C46 segment of the side chain was then appended via Julia-Kocienski olefination. The macrolide portion of phorboxazole A was completed by means of an Ando-Still-Gennari intramolecular (Z)-selective olefination at C2-C3 which required placement of a (dimethoxyphosphinyl)acetate moiety at C24. Final deprotection led to phorboxazole A via a route in which the longest linear sequence is 37 steps and the overall yield is 0.36%.
- Kuntiyong, Punlop,Lee, Tae Hee,Kranemann, Christian L.,White, James D.
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p. 7884 - 7899
(2013/07/05)
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- Enantioselective total synthesis of the antitumor macrolide rhizoxin D
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The convergent, highly enantioselective synthesis of rhizoxin D, a natural product possessing potent antitumor and antifungal bioactivity, is described. The C(1)-C(9) fragment of the molecule was synthesized utilizing a threefold pseudosymmetric intermediate ultimately derived from γ-butyrolactone. The central core of rhizoxin D was prepared via a chiral resolution/asymmetric aldol protocol. Several methods for the generation of the polyene fragment were explored, and the side-chain was ultimately prepared from serine in six steps. The unification of the left and right wings of the molecule was achieved using a one-step olefination protocol, and the macrocyclization was carried out using a Horner-Emmons olefination at the C(2)-C(3) olefin.
- Lafontaine, Jennifer A.,Provencal, David P.,Gardelli, Cristina,Leahy, James W.
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p. 4215 - 4234
(2007/10/03)
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- Total synthesis of rhizoxin D, a potent antimitotic agent from the fungus Rhizopus chinensis
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Rhizoxin D (2) was synthesized from four subunits, A, B, C, and D representing C3-C9, C10-C13, C14-C19, and C20-C27, respectively. Subunit A was prepared by cyclization of iodo acetal 21, which set the configuration at C5 of 2 through a stereoselective addition of the radical derived from dehalogenation of 21 at the β carbon of the (Z)-α,β-unsaturated ester. Aldehyde 29 was obtained from phenylthioacetal 24 and condensed with phosphorane 30, representing subunit B, in a Wittig reaction that gave the (E,E)-dienoate 31. This ester was converted to aldehyde 33 in preparation for coupling with subunit C. The latter in the form of methyl ketone 55 was obtained in six steps from propargyl alcohol. An aldol reaction of 33 with the enolate of 55 prepared with (+)-DIPCl gave the desired β-hydroxy ketone 56 bearing a (13S)-configuration in a 17-20:1 ratio with its (13R)-diastereomer. After reduction to anti diol 57 and selective protection as TIPS ether 58, the C15 hydroxyl was esterified to give phosphonate 59. An intramolecular Wadsworth-Emmons reaction of aldehyde 62, derived from δ-lactone 60, furnished macrolactone 63, which was coupled in a Stille reaction with stannane 68 to give 2 after cleavage of the TIPS ether.
- White, James D.,Blakemore, Paul R.,Green, Neal J.,Hauser, E. Bryan,Holoboski, Mark A.,Keown, Linda E.,Nylund Kolz, Christine S.,Phillips, Barton W.
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p. 7750 - 7760
(2007/10/03)
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- Intramolecular palladium(II)-mediated alkoxy carbonylation as a route to functionalized tetrahydropyrans. synthesis of the C9-C32 segment of phorboxazole A
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matrix presented Hydroxy alkene 12, synthesized stereoselectively from 2-methyloxazole-4-carboxaldehyde, underwent intramolecular methoxy carbonylation in the presence of palladium(II) acetate to give 13 in which all five stereogenic centers around the tetrahydropyran correspond to those in ring C of phorboxazole A. Aldehyde 15, derived from 13, was linked to hydroxy alkene 23 via a Wittig coupling, and the composite 25 was subjected to a second palladium(II) acetate mediated methoxy carbonylation to yield 26, accompanied by acetoxy ester 27.
- White, James D.,Kranemann, Christian L.,Kuntiyong, Punlop
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p. 4003 - 4006
(2007/10/03)
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- Rhizoxin synthetic studies. 2. Synthesis of the left hand [C(10) to C(19)] and polyene fragments
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The syntheses of the central core and the polyene fragments of the antitumor macrolide rhizoxin have been achieved in an efficient manner. The core has been prepared in enantiopure form via a asymmetric allylation/aldol protocol. The selective oxidation o
- Provencal, David P.,Gardelli, Cristina,Lafontaine, Jennifer A.,Leahy, James W.
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p. 6033 - 6036
(2007/10/02)
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- Synthesis of the Lower Subunit of Rhizoxin
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Full details of a study leading to a synthesis of the optically active C13-C26 lower subunit of rhizoxin including the side-chain chromophore characteristic of the full class of antimitotic agents are described.A key element of the synthesis is the stereoselective introduction of the C18-C19 trisubstituted olefin through use of a Wadsworth-Horner-Emmerson condensation of 3 with β-keto phosphonate 38 bearing resident functionality suitable for the diastereoselective introduction of C15-C17 employing a hydroxyl-directed reduction of the resultant β-hydroxy ketone.
- Boger, Dale L.,Curran, Timothy T.
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p. 2235 - 2244
(2007/10/02)
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