A convergent route to the CDEF-tetracycle of pectenotoxin-2

Rhodium-catalysed vinyl 1,4-conjugate addition coupled with Sharpless asymmetric dihydroxylation in the synthesis of the CDE ring fragment of pectenotoxin-4

Our synthesis of the CDE ring fragment of pectenotoxin-4 utilised two key steps to make the complex bicyclic ketal unit: (i) a rhodium-catalysed vinyl group 1,4-addition as the major C-C bond forming step; (ii) a stereoselective Sharpless Asymmetric Dihydroxylation (SAD) of the resulting 1,1-disubstituted homoallylic alcohol. Subsequent acid-catalysed cyclisation afforded the desired [5,6]-bicyclic ketal of the target molecule. This methodology was shown to be compatible with the desired E ring fragment 35 in order to construct the CDE fragment 37 of pectenotoxin-4.

Function-Oriented Studies Targeting Pectenotoxin 2: Synthesis of the GH-Ring System and a Structurally Simplified Macrolactone

A chemical foundation for function-oriented studies of pectenotoxin 2 (PTX2) is described. A synthesis of the bicyclic GH-system, and the design and synthesis of a PTX2-analogue, is presented. While maintaining critical features for actin binding, and lacking the Achilles’ heel for the natural product’s anticancer activity (the AB-spiroketal), this first-generation analogue did not possess the anticancer properties of PTX2, an observation that indicates the molecular significance of features present in the natural product’s CDEF-tetracycle.

Chiral Acylic Synthetic Intermediates from Readily Available Monoterpenoids

The preparation of some acyclic chiral synthetic intermediates from readily available monoterpenoids including citronellol, linalool and limonene, is reviewed. Some applications of these synthons are described.

Formation of tetrahydrofurans via a 5-endo-tet cyclization of aziridines--synthesis of (-)-pachastrissamine

The formation of tetrahydrofurans from 2-hydroxyalkyl-oxirane or aziridine is reported. The 5-endo-tet cyclization/ring opening of aziridine proceeded smoothly to give tetrahydrofurans (THFs) under mild conditions. In contrast, the corresponding process of oxirane was unsuccessful and a sequence of SN2 substitution/cyclization was required to form THFs. The application of the process to prepare ent-(-)-pachastrissamine is described.

Synthesis of the C1-C26 hexacyclic subunit of pectenotoxin 2

Synthesis of the C1-C26 hexacyclic subunit of pectenotoxin-2 (PTX-2) is described that features a stereoselective annulation to generate the C-ring by triple asymmetric Nozaki-Hiyama-Kishi coupling followed by oxidative cyclization. Preparation of the C1-C14 AB spriroketal-containing subunit employs a recently developed metallacycle-mediated reductive cross-coupling between a TMS-alkyne and a terminal alkene.

Synthesis of a pladienolide B analogue with the fully functionalized core structure

Starting from (R)-(-)-linalool (6), terminus differentiation and chain extension via aldol type reactions led to ketophosphonate 16 (C1-C8 building block). In a Horner-Wadsworth-Emmons reaction, 16 reacted with aldehyde 22, which contained the vicinal anti-Me-OH pattern and a vinyl iodide function, to provide the C1-C13 part of pladienolide B. After Shiina macrolactonization, reduction of the enone 26 gave the core structure 27. A Stille cross-coupling of vinyl iodide 27 with tributylphenylstannane eventually furnished analogue 30.