Synthetic prodrug design enables biocatalytic activation in mice to elicit tumor growth suppression

Considering the intrinsic toxicities of transition metals, their incorporation into drug therapies must operate at minimal amounts while ensuring adequate catalytic activity within complex biological systems. As a way to address this issue, this study investigates the design of synthetic prodrugs that are not only tuned to be harmless, but can be robustly transformed in vivo to reach therapeutically relevant levels. To accomplish this, retrosynthetic prodrug design highlights the potential of naphthylcombretastatin-based prodrugs, which form highly active cytostatic agents via sequential ring-closing metathesis and aromatization. Structural adjustments will also be done to improve aspects related to catalytic reactivity, intrinsic bioactivity, and hydrolytic stability. The developed prodrug therapy is found to possess excellent anticancer activities in cell-based assays. Furthermore, in vivo activation by intravenously administered glycosylated artificial metalloenzymes can also induce significant reduction of implanted tumor growth in mice.

Chiron approach for the total synthesis of brevipolide M

An efficient stereoselective synthesis of brevipolide M was established in 13 linear steps and 17.8% overall yields base on chiron approach. The key steps of our synthesis involved tandem homologation / tetrahydrofuran cyclization and sequential ring-closing metathesis (RCM) / double-bond migration in one-pot processes.

Olefin Metathesis in Confinement: Towards Covalent Organic Framework Scaffolds for Increased Macrocyclization Selectivity

Covalent organic frameworks (COFs) offer vast structural and chemical diversity enabling a wide and growing range of applications. While COFs are well-established as homogeneous catalysts, so far, their high and ordered porosity has scarcely been utilized to its full potential when it comes to spatially confined reactions in COF pores to alter the outcome of reactions. Here, we present a highly porous and crystalline, large-pore COF as catalytic support in diene ring-closing metathesis reactions, leading to increased macrocylization selectivity. COF pore-wall modification by immobilization of a Grubbs-Hoveyda-type catalyst via a mild silylation reaction provides a molecularly precise heterogeneous metathesis catalyst. An increased macro(mono)cyclization (MMC) selectivity over oligomerization (O) for the heterogeneous COF-catalyst (MMC:O = 1.30) of up to 44% compared to the homogeneous catalyst (MMC:O = 0.90) was observed along with a substrate-size dependency in selectivity, pointing to diffusion limitations induced by the pore confinement.

Synthesis of highly stable dual-site immobilized ruthenium olefin metathesis catalyst without ru leaching

The tri-block copolymer is used as a carrier to simultaneously immobilize the N-heterocyclic and benzylidene ligands precursor of the Ru-based catalyst to form a dual-site immobilized catalyst. The dual-site immobilized catalyst can catalyze ring-opening metathesis polymerization, ring-closing metathesis and self-metathesis. The dual-site immobilized catalyst shows good heterogeneity in dichloromethane, which simplifies the purification of product and recovery of catalyst. The dual-site immobilized catalyst exhibits excellent activity and recycling performance. The excellent recyclability can be attributed to the capture of ruthenium by the excess ligands precursor on carrier. Importantly, ruthenium residues are not detected in product.

Chasing "Zampanalogs": Advancing the Synthesis of the Zampanolide Macrocycle

<p>(-)-Zampanolide (1), a natural product isolated from a marine sponge, is a microtubule-stabilizing agent that exhibits activity in the nanomolar range against various cancer cells, including in P-gp pump overexpressing cells. This attribute makes (-)-zampanolide an interesting target for further investigation. In this work, a new method for a modular and convergent total synthesis of optically pure zampanolide was investigated, which would also allow the generation of “zampanalogs” following the same basic strategy. Their biological activity may then be assessed to allow the elucidation of structure-activity relationships of (-)-zampanolide and its analogs in tubulin binding. The synthetic plan consisted of the modular combination of four major fragments, which would be connected in the late stages of the synthesis and could therefore be easily exchanged to allow the generation of analogs. The C15-C16 bond would be connected via an alkynylation reaction, and a subsequent reductive methylation would install the trisubstituted alkene. The connections at C1 and C3 could be achieved through a Bestmann ylid linchpin reaction, while the macrolactonization would be completed using a ring-closing metathesis to form the C8-C9 alkene. The side chain could be attached at C20 using one of the established aza-aldol methods. The fragments necessary for the formation of the macrocycle were synthesized successfully. The purification strategy throughout the synthetic route was rationalized and provides an improvement with respect to yield and time compared to work previously done in this research group. Alongside these fragments, modified fragments that were originally intended to serve as model systems were synthesized, which could also be used as building blocks in the synthesis of “zampanalogs”. Several methods for a stereoselective alkynylation at C15 were tested. These led to only meager successes, so an approach using a non-stereoselective alkynylation, followed by oxidation and a stereoselective CBS-reduction, was chosen. For the installation of the trisubstituted alkene a reductive methylation with vitride was tested, but this only led to the reduction of the alkyne without methylation. This product may be employed for the synthesis of C17-desmethyl analogs. The reductive methylation at C16-C17 was ultimately achieved using the Gilman reagent in a similar manner to the installation of the C5 methyl group in the C3-C8 fragment. A linchpin strategy with the Bestmann ylid simultaneously formed the connectivity at C1 and C3. This process was successfully performed on multiple substrates arising from the model systems used in the alkynylation and reductive methylation reactions, yielding precursors to the ring-closing metathesis and potentially enabling the synthesis of various analogs. The ring-closing metathesis proved to be difficult in analogs lacking the C17 methyl group and cis-tetrahydropyran ring, and due to this tendency further investigations are necessary. Once the macrocycle has been closed, a global deprotection and oxidation of hydroxy groups is necessary to allow for the installation of the sidechain.</p>

Chasing "Zampanalogs": Advancing the Synthesis of the Zampanolide Macrocycle

<p>(-)-Zampanolide (1), a natural product isolated from a marine sponge, is a microtubule-stabilizing agent that exhibits activity in the nanomolar range against various cancer cells, including in P-gp pump overexpressing cells. This attribute makes (-)-zampanolide an interesting target for further investigation. In this work, a new method for a modular and convergent total synthesis of optically pure zampanolide was investigated, which would also allow the generation of “zampanalogs” following the same basic strategy. Their biological activity may then be assessed to allow the elucidation of structure-activity relationships of (-)-zampanolide and its analogs in tubulin binding. The synthetic plan consisted of the modular combination of four major fragments, which would be connected in the late stages of the synthesis and could therefore be easily exchanged to allow the generation of analogs. The C15-C16 bond would be connected via an alkynylation reaction, and a subsequent reductive methylation would install the trisubstituted alkene. The connections at C1 and C3 could be achieved through a Bestmann ylid linchpin reaction, while the macrolactonization would be completed using a ring-closing metathesis to form the C8-C9 alkene. The side chain could be attached at C20 using one of the established aza-aldol methods. The fragments necessary for the formation of the macrocycle were synthesized successfully. The purification strategy throughout the synthetic route was rationalized and provides an improvement with respect to yield and time compared to work previously done in this research group. Alongside these fragments, modified fragments that were originally intended to serve as model systems were synthesized, which could also be used as building blocks in the synthesis of “zampanalogs”. Several methods for a stereoselective alkynylation at C15 were tested. These led to only meager successes, so an approach using a non-stereoselective alkynylation, followed by oxidation and a stereoselective CBS-reduction, was chosen. For the installation of the trisubstituted alkene a reductive methylation with vitride was tested, but this only led to the reduction of the alkyne without methylation. This product may be employed for the synthesis of C17-desmethyl analogs. The reductive methylation at C16-C17 was ultimately achieved using the Gilman reagent in a similar manner to the installation of the C5 methyl group in the C3-C8 fragment. A linchpin strategy with the Bestmann ylid simultaneously formed the connectivity at C1 and C3. This process was successfully performed on multiple substrates arising from the model systems used in the alkynylation and reductive methylation reactions, yielding precursors to the ring-closing metathesis and potentially enabling the synthesis of various analogs. The ring-closing metathesis proved to be difficult in analogs lacking the C17 methyl group and cis-tetrahydropyran ring, and due to this tendency further investigations are necessary. Once the macrocycle has been closed, a global deprotection and oxidation of hydroxy groups is necessary to allow for the installation of the sidechain.</p>