Mark A. Rizzacasa

Synthesis of biotinylated episilvestrol: highly selective targeting of the translation factors eIF4AI/II.

Silvestrol (1) and episilvestrol (2) are protein synthesis inhibitors, and the former has shown efficacy in multiple mouse models of cancer; however, the selectivity of these potent cytotoxic natural products has not been described. Herein, it is demonstrated that eukaryotic initiation factors eIF4AI/II were the only proteins detected to bind silvestrol (1) and biotinylated episilvestrol (9) by affinity purification. Our study demonstrates the remarkable selectivity of these promising chemotherapeutics.

Translation inhibitors induce cell death by multiple mechanisms and Mcl-1 reduction is only a minor contributor

There is significant interest in treating cancers by blocking protein synthesis, to which hematological malignancies seem particularly sensitive. The translation elongation inhibitor homoharringtonine (Omacetaxine mepesuccinate) is undergoing clinical trials for chronic myeloid leukemia, whereas the translation initiation inhibitor silvestrol has shown promise in mouse models of cancer. Precisely how these compounds induce cell death is unclear, but reduction in Mcl-1, a labile pro-survival Bcl-2 family member, has been proposed to constitute the critical event. Moreover, the contribution of translation inhibitors to neutropenia and lymphopenia has not been precisely defined. Herein, we demonstrate that primary B cells and neutrophils are highly sensitive to translation inhibitors, which trigger the Bax/Bak-mediated apoptotic pathway. However, contrary to expectations, reduction of Mcl-1 did not significantly enhance cytotoxicity of these compounds, suggesting that it does not have a principal role and cautions that strong correlations do not always signify causality. On the other hand, the killing of T lymphocytes was less dependent on Bax and Bak, indicating that translation inhibitors can also induce cell death via alternative mechanisms. Indeed, loss of clonogenic survival proved to be independent of the Bax/Bak-mediated apoptosis altogether. Our findings warn of potential toxicity as these translation inhibitors are cytotoxic to many differentiated non-cycling cells.

Synthetic studies towards the squalestatins and zaragozic acids

Abstract A synthesis of a model core system ( 18 ) of the squalestatins and zaragozic acids has been achieved from D-mannose. The key steps involve an Ireland-Claisen rearrangement of the allyl ester 5 and a stereoselective epoxidation of the furanoid glycal 12 with 2,2-dimethyldioxirane.

Synthesis of the core of apicularen A by transannular conjugate addition

The synthesis of the core of the myxobacteria metabolite apicularen A by a novel transannular 1,4-addition is described. The key step involved acid mediated transannular conjugate addition of the C13 hydroxyl into the α,β-unsaturated ketone in macrolactone 18 to provide the trans-pyranone 19 and the cis-isomer 20 in a ratio of 9:1, respectively.

Total synthesis of 8-deshydroxyajudazol B.

The total synthesis of a stereoisomer of 8-deshydroxyajudazol B (4), the putative biosynthetic intermediate of the ajudazols A (1) and B (2), is described. The key steps in the synthesis included an intramolecular Diels-Alder (IMDA) reaction to secure the isochromanone fragment, a novel selective acylation/O,N-shift to give a hydroxyamide which was cyclized to the oxazole and a high yielding Sonogashira coupling to form the C18-C19 bond. Partial alkyne reduction then afforded the target 4.

Synthetic studies on the salicylihalamides: macrolactone formation via ring closing metathesis versus macrolactonization

Abstract Two routes to the unusual 12-membered unsaturated benzolactone of the highly cytotoxic marine metabolites the salicylihalamides are presented. The first involves an RCM step to construct the C9C10 alkene bond and this provided the model macrolactones 9 and 10 in a ratio of 77:23, respectively. An alternative route involved a Stille coupling to construct the C8C9 bond followed by a macrolactonization to give the lactones 9 and 10 in a ratio of 96:4.

Total synthesis of the marine sponge metabolites (+)-rottnestol, (+)-raspailol A and (+)-raspailol BTaken in part from the PhD thesis of I. R. Czuba, The University of Melbourne, 2002.

The asymmetric syntheses of (+)-rottnestol (1) and the related marine sponge metabolites (+)-raspailols A (5) and B (6) are described. The key step in each of these sequences was a Stille coupling to form the C9-C10 sp2-sp2 bond and connect the polyene sidechains to the appropriate optically active tetrahydropyran core. For rottnestol (1), both C12 epimers were synthesised by a coupling between stannane 7 and (R)- or (S)-8 followed by acid hydrolysis which allowed for the assignment of the absolute configuration at the remote C12 stereocentre as R upon comparison of chiroptical data of the synthetic material with that reported for the natural product. In accord with this, (12R)-raspailol A (5) was synthesised from stannane 7 and sidechain 9 and this compound also compared well with the data for natural material including sign and absolute value of the specific rotation. Finally, the same C12 epimer of raspailol B (6) was secured via a union between stannane 10 and iodide 9 and this also possessed a similar rotation to that described for the natural product. Thus, all three compounds appear to possess the (12R) configuration, while that of the core tetrahydropyran ring is the same as proposed originally.

Synthetic approaches to the alkaloids of the ancistrocladaceae: (–)-O-methylancistrocladine and (+)-O-methylhamatine

An asymmetric total synthesis of the naphthylisoquinoline alkaloid (–)-O-methylancistrocladine (2) is described; the synthetic method also provides routes to the atropisomer O-methylhamatine (4) and the enantiomers of these alkaloids.

Enantiospecific synthesis of the phospholipase A2 inhibitors (−)-cinatrin C1 and (+)-cinatrin C3

The enantiospecific synthesis of (-)cinatrin C1 (3) and (+)-cinatrin C3 (5) from the D-arabinose derivative 9 is described. The stereochemistry at C2 was introduced via a chelation-controlled addition of a carbanion to alpha-hydroxy ketone 8. The best selectivity was achieved by use of the Grignard reagent derived from trimethylsilylacetylene. Transformation of the terminal alkyne into methyl ester 17 followed by acetal hydrolysis and selective lactol oxidation gave cinatrin C1 dimethyl ester (7). Base hydrolysis and acid induced relactonization then gave a 1:1 mixture of cinatrins C1 (3) and C3 (5).

Total Synthesis of (+)-Crocacin A

The first asymmetric synthesis of (+)-crocacin C (3) is described which served to confirm the absolute configuration of this compound. The key step in the sequence was the stereoselective assembly of the (E,E)-diene amide side chain by a Stille cross-coupling between the stannane 5 and vinyl iodide 6.