A unified strategy for the total syntheses of eribulin and a macrolactam analogue of halichondrin B.

A unified synthetic route for the total syntheses of eribulin and a macrolactam analog of halichondrin B is described. The key to the success of the current synthetic approach includes the employment of our reverse approach for the construction of cyclic ether structural motifs and a modified intramolecular cyclization reaction between alkyl iodide and aldehyde functionalities to establish the all-carbon macrocyclic framework of eribulin. These syntheses, together with our previous work on the total syntheses of halichondrin B and norhalichondrin B, demonstrate and validate the powerful reverse approach in the construction of cyclic ether structural motifs. On the other hand, the unified synthetic strategy for the synthesis of the related macrolactam analog provides inspiration and opportunities in the halichondrin field and related polycyclic ether areas.

A Highly Convergent Total Synthesis of Norhalichondrin B.

A new synthetic strategy for the total synthesis of norhalichondrin B featuring a highly convergent approach and our recently disclosed reverse approach for the synthesis of cyclic ether structural motifs is disclosed. Resulting in the shortest route to norhalichondrin B disclosed thus far, the reported total synthesis was achieved through the synthesis of two almost equally complex fragments whose coupling and short elaboration sequence featured an essential epimerization of the C16 stereocenter occurring concurrently with a simple acid-induced deprotection, a tactic based on a prior study along the synthetic route. This unprecedented strategy within the halichondrin family of natural products could find practical application to the synthesis of other more or less complex natural or designed halichondrin analogues.

A Reverse Approach to the Total Synthesis of Halichondrin B.

A new strategy is described for the total synthesis of halichondrin B featuring reversal of the sequential construction of a number of its cyclic ethers from the classical approach by instead forming C-O bonds first followed by C-C bond formation. Employing the Nicholas reaction to generate linear ethers as precursors for the total synthesis of halichondrin B and other members of the halichondrin and eribulin families of compounds, this novel approach provides new opportunities for the development of improved syntheses of these complex and valuable compounds. In this Article, we report the syntheses of defined fragments I, MN, EFG, and A. Fragments I and MN were then coupled and elaborated to advanced intermediate IJKLMN, which was joined with fragment EFG to afford, after appropriate elaboration and macrolactonization, the more advanced polycyclic intermediate EFGHIJKLMN. Elaboration of the latter and coupling with fragment A followed by further functionalization completed the total synthesis of halichondrin B through a short and convergent pathway.

Design, Synthesis, and Biological Evaluation of Tubulysin Analogues, Linker-Drugs, and Antibody-Drug Conjugates, Insights into Structure-Activity Relationships, and Tubulysin-Tubulin Binding Derived from X-ray Crystallographic Analysis.

Molecular design, synthesis, and biological evaluation of tubulysin analogues, linker-drugs, and antibody-drug conjugates are described. Among the new discoveries reported is the identification of new potent analogues within the tubulysin family that carry a C11 alkyl ether substituent, rather than the usual ester structural motif at that position, a fact that endows the former with higher plasma stability than that of the latter. Also described herein are X-ray crystallographic analysis studies of two tubulin-tubulysin complexes formed within the α/ß interface between two tubulin heterodimers and two highly potent tubulysin analogues, one of which exhibited a different binding mode to the one previously reported for tubulysin M. The X-ray crystallographic analysis-derived new insights into the binding modes of these tubulysin analogues explain their potencies and provide inspiration for further design, synthesis, and biological investigations within this class of antitumor agents. A number of these analogues were conjugated as payloads with appropriate linkers at different sites allowing their attachment onto targeting antibodies for cancer therapies. A number of such antibody-drug conjugates were constructed and tested, both in vivo and in vitro, leading to the identification of at least one promising ADC (Herceptin-LD3), warranting further investigations.

Divergent Total Syntheses of Enmein-Type Natural Products: (-)-Enmein, (-)-Isodocarpin, and (-)-Sculponin†R.

Divergent total syntheses of the enmein-type natural products (-)-enmein, (-)-isodocarpin, and (-)-sculponin R have been achieved in a concise fashion. Key features of the strategy include 1) an efficient early-stage cage formation to control succeeding diastereoselectivity, 2) a one-pot acylation/akylation/lactonization to construct the C-ring and C8 quarternary center, 3) a reductive alkenylation approach to construct the enmain D/E rings and 4) a flexible route to allow divergent syntheses of three natural products.

Enantioselective Total Synthesis of (+)-Steenkrotin†A and Determination of Its Absolute Configuration.

The first enantioselective total synthesis of (+)-steenkrotin A has been achieved in 18 steps and 4.2 % overall yield. The key features of the strategy entail a Rh-catalyzed O-H bond insertion followed by an intramolecular carbonyl-ene reaction, two sequential SmI2 -mediated Ueno-Stork and ketyl-olefin cyclizations, and a cascade intramolecular aldol condensation/vinylogous retro-aldol/aldol process with inversion of the relative configuration at the C7 position. The absolute configuration of (+)-steenkrotin A was determined based on the stepwise construction of the stereocenters during the total synthesis.

Total synthesis of diterpenoid steenkrotin A.

A concise and diastereoselective total synthesis of the diterpenoid (±)-steenkrotin A is described for the first time. The strategy mainly features three key ring formations: 1) a rhodium-catalyzed O-H bond insertion followed by an intramolecular carbonyl-ene reaction to build up the tetrahydrofuran subunit; 2) sequential SmI2 -mediated Ueno-Stork and ketyl-olefin cyclizations to construct the [5,7] spirobicyclic skeleton; and 3) an intramolecular aldol condensation/vinylogous retro-aldol/aldol sequence to form the final six-membered ring with inversion of the relative configuration at the C7 position.

Construction of the tricyclic core of steenkrotin-type diterpenoids via intramolecular [3 + 2] cycloaddition.

A concise and diastereoselective route to the angularly fused [5-6-7] tricyclic carbon framework of the steenkrotin-type diterpenoids was reported. The key features of the strategy are based on an intramolecular nitrile oxide/alkene [3 + 2] cycloaddition and a regio-selective aldol/dehydration sequence.