Polypropionate subunits

Scheme 9.3. Stereocontrolled strategy for iterative assembly of enantiopure polypropionate subunits.

Bonini, C. Chiummiento, L. Funicello, M. Marconi, L. Righi, G. Chiral polypropionate subunit by a chemoenzymatic approach. Tetrahedron Asymmetry 1998, 9, 2559-2561. 

In 1998, Marshall and co-workers demonstrated the utility of allenyl metal addition methodology for the synthesis of the polypropionate subunits contained in discodermolide [53,54], As outlined in Scheme 18, Marshall divided the carbon backbone... 

Dolabriferol was isolated from Dolabrifera dolabrifera, a shell-less mollusk. This natural product is made of two polypropionate subunits linked by an ester function, a structural motif that is also found in baconipyrones A-D (see section 4.3). Dolabriferol is assumed to protect the mollusk from predators. When the Vogel s cascade... 

Hanessian S, Wang WG, Gai YH, Olivier E. A general and stereocontrolled strategy for the iterative assembly of enan-tiopure polypropionate subunits synthesis of the C19-C28 segment of rifamycin S from a single chiron. J. Am. Chem. Soc. 1997 119(42) 10034-10041. 

For cyclic alkenes, the stereochemical outcome of hydroborations can most often be predicted on the basis of an analysis of the preferred ground-state conformation of the ring. Danishefsky s synthesis of the polypropionate subunit 79 of rifamycin S serves as an illustrative example (Scheme 7.14) [30]. In this synthetic endeavor, hydroboration of pyrene 76 affords pyranose 78 in 68 % yield with high regio- and diastereocontrol believed to result from transition structure 77. 

Panek and co-workers reported their synthesis of discodermolide in 2005 [62, 63], relying on the application of their crotylsilane methodology for the synthesis of polypropionate motifs [155,156] (see [157] forareview) [158,159,182], Their strategy involved key bond disconnections at C6-C7 and C14-05, based on an aldol coupling and the established Suzuki cross-coupling respectively, employing the key subunits 137 (C1-C6), 138 (C7-C14) and 81 (C15-C24) (Scheme 29). 

In 2007, Betzer, Ardisson and co-workers reported their synthesis of discodermo-lide [64] following the Marshall disconnection strategy of C7-C8 acetylide addition and Suzuki cross-coupling at C14-05 (Scheme 32) [53, 54], The synthesis of the key subunits 160 (C1-C7), 161 (C8-C14) and 162 (C15-C24) demonstrated the versatility of the Hoppe crotyltitanation reaction [166-169] in the synthesis of polypropionate motifs, using the incorporated (Z)-0-enecarbamate to configure the requisite alkene substitution patterns [170, 171],... 

Further work from Calter and Bi extended this successfid methylketene dimerization to the synthesis of an antibiotic subunit from the Pamamycin family at the time an unsynthesized class of natural products [57]. Extensions of the methodology demonstrated the stereocontrolled synthesis of polypropionates [58] via an in situ aldol reaction. Both anhydrides 106 (Scheme 3.23) and acid chlorides 1 (Scheme 3.24) were exploited as suitable ketene precursors. 

A different strategy that has also been well smdied for polypropionate synthesis is the hetero-Diels-Alder (HDA) reaction. The Danishefsky group has reported on one of the first attempts to obtain polypropionates via this method-ology. His group focused on the pyran subunit, a... 

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