We report a stereoselective synthesis of the C22-C28 substituted tetrahydropyran fragment of eribulin, using commercially available isoascorbic acid as the starting material. This synthetic route features a highly efficient sequence of reactions, including lactonization, conjugate addition, and an intramolecular oxa-Michael addition, which serve as the key transformations. The approach provides access to the desired tetrahydropyran fragment in a concise and stereoselective manner.

Herein, we report a practical stereoselective synthesis of C14-C21 and C15-C21 tetrahydrofuran-based fragment of eribulin using two different approaches. The approach utilizes iodoetherification and intra molecular oxa-Michael additions as key steps in individual approaches using R,R-tartaric acid and L-ascorbic acids as cost effective chiral starting materials.

A practical stereoselective synthesis of the central C1-C10 fragment of eribulin and its two diastereomeric analogues is developed. Our approach relied on the use of L-ascorbic acid as the starting material which allowed accessing a key intermediate with a syn diol moiety (C9 and C10 of eribulin) and a carboxylic ester group. A functionalized six membered lactone having several required hydroxyl groups was then obtained. In a number of steps, the lactone was converted to an intermediate for our key oxa-Michael reaction. A regio- and stereocontrolled intramolecular oxa-Michael reaction completed the synthesis of the C1-11 fragment having a trans-fused tetrahydropyrans with the exact stereochemistry of various hydroxyl groups, as in eribulin. (C) 2019 Published by Elsevier Ltd.

Over the years, rapamycin has attracted serious attention due to its remarkable biological properties and as a potent inhibitor of the mammalian target of rapamycin (mTOR) protein through its binding with FKBP-12. Several efficient strategies that utilize synthetic and biosynthetic approaches have been utilized to develop small molecule rapamycin analogs or for synthesizing hybrid compounds containing a partial rapamycin structure to improve pharmacokinetic properties. Herein, we report selected case studies related to the synthesis of rapamycin-derived compounds and hybrid molecules to explore their biological properties.

Inspired from geldanamycin, the synthesis of a new series of 20-membered macrocyclic compounds is developed. The key features in our design are (i) retention of the fragment having the precise chiral functional groups of geldanamycin at C10, C11, C12 and C14, and (ii) replacement of an olefin moiety with the ester group, and the quinoid sub-structure with the triazole ring. The southern fragment needed for the macrocyclic ring formation was obtained from Evans' syn aldol as the key reaction and with the use of D-mannitol as the cheap source of a chiral starting material. For the synthesis of the northern fragment, we utilized l-ascorbic acid, which provided the desired chiral functional groups at C6 and C7. Further, the chain extension completed the synthesis of the northern fragment. In our approach, the crucial 20 membered macrocyclic ring was formed employing the click chemistry. When tested for their ability to directly trans-differentiate human mesenchymal stem cells to neurons, two novel compounds (20a and 7) from this series were identified and this was further validated by the presence of specific neuronal biomarkers (i.e. nestin, agrin and RTN4).

Aberrant apoptosis can lead to acute or chronic degenerative diseases. Mitochondrial outer membrane permeabilization (MOMP) triggered by the oligomerization of the Bcl-2 family proteins Bax/Bak is an irreversible step leading to execution of apoptosis. Here, we describe the discovery of small-molecule inhibitors of Bax/Bak oligomerization that prevent MOMP. We demonstrate that these molecules disrupt multiple, but not all, interactions between Bax dimer interfaces thereby interfering with the formation of higher-order oligomers in the MOM, but not recruitment of Bax to the MOM. Small-molecule inhibition of Bax/Bak oligomerization allowed cells to evade apoptotic stimuli and rescued neurons from death after excitotoxicity, demonstrating that oligomerization of Bax is essential for MOMP. Our discovery of small-molecule Bax/Bak inhibitors provides novel tools for the investigation of the mechanisms leading to MOMP and will ultimately facilitate development of compounds inhibiting Bax/Bak in acute and chronic degenerative diseases.

A simple, practical stereoselective synthesis of the epothilone fragment is developed to obtain a diverse set of expanded 18-membered macrocyclic compounds. These macrocycles contain the C5–C8 sub-unit of epothilone and an additional amino acid moiety incorporated in the 18-membered macrocycle, which allows the synthesis of several analogs with a variation in the chiral side chain. The epothilone fragment was obtained by using an enantiopure epoxide, which was subjected to a regioselective opening, giving the key derivative. Finally, the synthesis of the 18-membered macrocyclic ring was achieved by employing two key steps: (i) acylation with an N-allylated amino acid moiety, and (ii) a ring-closing metathesis (RCM) approach. Computational studies of the macrocyclic compounds obtained from this study with actin give rise to the proposed molecular interactions with the target protein. Further, the screening of our chemical toolbox from this program (i.e., the final products and several intermediates) identified several compounds as promoters of apoptosis in patient-derived brain tumor glioma cells.

A practical and scalable stereoselective synthesis of the western substituted tetrahydrofuran ring C27-C35 fragment of eribulin was developed by using (2S,3S)-tartaric acid as a cheap starting material that was converted into an intermediate through a stereoselective vinylation and cross-metathesis as the key steps. A regio- and stereoselective intramolecular oxy-Michael cyclization or an iodocyclization reaction finally provided the required western tetrahydrofuran ring fragment and its related isomeric analogues. These key fragments were further utilized in obtaining several types of macrocyclic derivatives for exploration of their biological properties. The simplicity of our present approach has the potential to be considered for large-scale syntheses of key fragments of eribulin and related analogues.

A practical stereoselective synthesis to obtain the substituted furan ring as the substructure of eribulin is developed. An asymmetric syn-aldol and intramolecular oxy-Michael were two key steps in our approach. The functionalized furan derivatives were then utilized further to build the 14- and 12-membered macrocyclic diversity as trans- and cis-fused (C-29 and C-30) compounds. This is the first report of building a chemical toolbox with macrocyclic small molecules having trans- or cis-fused 14- or 12-membered rings containing the substructure of eribulin and its diastereomer.

We developed a regio- and stereocontrolled Dieckmann cyclization approach to the synthesis of a novel, natural-product-like scaffold that was inspired from treprostinil (UT-15). This was further utilized in a diversity-based, 15-membered macrocyclic synthesis of two different sets of hybrid compounds. The amino acid moiety embedded in the macrocyclic skeleton allow exploring various chiral side chain groups within the ring.

Modulators of microtubule dynamics have received increasing attention because of their potential to stop cancer growth. Although it belongs to the category of complex protein–protein interactions (PPIs), which are generally considered difficult to modulate through small molecules, the use of microtubule is considered a well-validated target. There are a number of bioactive natural products and related compounds that are currently in use as drugs or in clinical trials as next generation anti-cancer agents. The present review article is focused on two such bioactive natural products, epothilone and halichondrin B, and covers some of the key papers published after 2005 that outline various synthetic approaches to obtain next generation structural analogs as well as the synthesis of hybrid compounds.

A divergent approach to obtain a latrunculin family based hybrid macrocyclic toolbox is developed. A practical, stereoselective synthesis of a common substructure present in latrunculin A and latrunculol A was achieved. This was further utilized in the macrocyclic diversity synthesis. The amino acid moiety embedded in the 15-membered macrocyclic ring allows for the exploration of various chiral side chains as one of the diversity sites.

Mitochondria produce the majority of cellular energy through the process of oxidative phosphorylation and play a central role in regulating the functionality and survival of eukaryotic cells. Under physiological stress, mitochondrial membrane permeabilization results in the release of apoptogenic material such as cytochrome c in the cytoplasm, which thereby initiates caspase activation and the consequent cell death. In our present study, we screened a series of compounds for their ability to inhibit mitochondrial membrane permeabilization and to prevent cytochrome c release during the endoplasmic reticulum stress in cultured pancreatic β-cells. Three benzofuran-based macrocyclic small molecules, that is, 2.4c, c104, and c108, were found to restore the depolarization of mitochondrial membrane potential and to prevent the release of cytochrome c from mitochondria. Interestingly, the acyclic precursor of 2.4c (i.e., 2.3c) did not show any effect, whereas the macrocyclic derivative obtained by utilizing ring-closing metathesis as the “stitching technology” led to this function. The macrocyclic architecture seems to play a crucial role in presenting various functional moieties in the right orientation to observe this effect.

We report the synthesis of four different types of macrocyclic-derived glycohybrids from carbohydrates that have an amino acid moiety in the large-ring skeleton. These macrocyclic glycohybrids were obtained from -C-1H- and -C-1H-linked carbohydrates. In one series, we utilized ring-closing metathesis as the stitching technology to obtain two different macrocycles, i.e., trans equatorial-axial C-1H and C-5H and cis axial-axial C-1H and C-5H. The click approach was the key reaction in our second series to obtain two other macrocyclic compounds, i.e., trans equatorial-axial C-1H and C-5H and cis axial-axial C-1H and C-5H. The evaluation of this toolbox resulted in the identification of two unique compounds as antiangiogenesis agents in an embryonic zebrafish assay. Interestingly, in both cases, the macrocyclic compounds that have a cis relationship (i.e., axial-axial orientation) between C-1H and C-5H showed activity and their other diastereomers (i.e., equatorial-axial C-1H and C-5 H) with a trans relationship did not show any effect.

A practical and modular approach to obtain a diverse set of 14-membered macrocyclic compounds from carbohydrates is developed that utilizes functional groups at C-1 and C-5. The evaluation of this toolbox in various zebrafish assays led to the identification of 2.7f as an antiangiogenesis agent.

A modular approach to explore the macrocyclic chemical space around an aminoindoline scaffold is developed. This is achieved by incorporating an amino acid moiety and subsequent stitching technology. Through screening of a zebrafish assay, several antiangiogenesis agents are identified.

We report a practical and modular approach to obtain two different types of 17-membered ring macrocyclic compounds through an intramolecular Heck reaction. These macrocyclic compounds are functionalized, that is, they contain two contiguous stereogenic hydroxy functional groups and an amino acid moiety in the macrocyclic ring skeleton. The macrocycles were then screened against a zebrafish assay to determine the antiangiogenesis activity of these small molecules. Macrocyclic compound 2.2a was identified as a potent inhibitor at 2.5 M, whereas its acyclic precursor and the other related macrocyclic compounds did not show any effect.

A highly practical and modular synthesis to obtain a diverse 14-membered ring-based macrocyclic toolbox is achieved. These compounds were further tested in zebrafish assays related to early embryonic development, angiogenesis, and neurogenesis, respectively. 1.4c was Identified as an antiangiogenesis agent.