Syntheses of (+)-30-epi-, (-)-6-epi-, (±)-6,30-epi-13,14-didehydroxyisogarcinol and (±)-6,30-epi-garcimultiflorone A utilizing highly diastereoselective, Lewis acid-controlled cyclizations

The first syntheses of 13,14-didehydroxyisogarcinol (6) and garcimultiflorone A (5) stereoisomers are reported in six steps from a commercially available phloroglucinol. Lewis acid-controlled, diastereoselective cationic oxycyclizations enabled asymmetric syntheses of (-)-6-epi-6 and (+)-30-epi-6. A similar strategy enabled production of the meso-dervied isomers (±)-6,30-epi-6 and (±)-6,30-epi-5. Finally, a convenient strategy for gram scale synthesis was developed utilizing diastereomer separation at a later stage in the synthesis that minimized the number of necessary synthetic operations to access all possible stereoisomers.R01 GM073855 - NIGMS NIH HHS; R24 GM111625 - NIGMS NIH HHS; R35 GM118173 - NIGMS NIH HH

Photochemical Approaches to Complex Chemotypes: Applications in Natural Product Synthesis.

The use of photochemical transformations is a powerful strategy that allows for the formation of a high degree of molecular complexity from relatively simple building blocks in a single step. A central feature of all light-promoted transformations is the involvement of electronically excited states, generated upon absorption of photons. This produces transient reactive intermediates and significantly alters the reactivity of a chemical compound. The input of energy provided by light thus offers a means to produce strained and unique target compounds that cannot be assembled using thermal protocols. This review aims at highlighting photochemical transformations as a tool for rapidly accessing structurally and stereochemically diverse scaffolds. Synthetic designs based on photochemical transformations have the potential to afford complex polycyclic carbon skeletons with impressive efficiency, which are of high value in total synthesis.R01 GM073855 - NIGMS NIH HHS; R01 GM096129 - NIGMS NIH HHS; R35 GM118173 - NIGMS NIH HH

A photochemical flow reactor for large scale syntheses of aglain and rocaglate natural product analogues

Published in final edited form as: Bioorg Med Chem. 2017 Dec 1; 25(23): 6197–6202. Published online 2017 Jun 11. doi: [10.1016/j.bmc.2017.06.010]Herein, we report the development of continuous flow photoreactors for large scale ESIPT-mediated [3+2]-photocycloaddition of 2-(p-methoxyphenyl)-3-hydroxyflavone and cinnamate-derived dipolarophiles. These reactors can be efficiently numbered up to increase throughput two orders of magnitude greater than the corresponding batch reactions.Financial support from Boston University and National Institutes of Health (ABB R33AI105944) is gratefully acknowledged. We thank Dr. Norman Lee (Boston University) for high-resolution mass spectrometry data. NMR (CHE-0619339) and MS (CHE-0443618 facilities at Boston University are supported by the NSF. (Boston University; ABB R33AI105944 - National Institutes of Health; CHE-0619339 - NSF; CHE-0443618 - NSF)Accepted manuscrip

Translation inhibition by rocaglates is independent of eIF4E phosphorylation status

Rocaglates are natural products that inhibit protein synthesis in eukaryotes and exhibit antineoplastic activity. In vitro biochemical assays, affinity chromatography experiments coupled with mass spectrometry analysis, and in vivo genetic screens have identified eukaryotic initiation factor (eIF) 4A as a direct molecular target of rocaglates. eIF4A is the RNA helicase subunit of eIF4F, a complex that mediates cap-dependent ribosome recruitment to mRNA templates. The eIF4F complex has been implicated in tumor initiation and maintenance through elevated levels or increased phosphorylation status of its cap-binding subunit, eIF4E, thus furthering the interest toward developing rocaglates as antineoplastic agents. Recent experiments have indicated that rocaglates also interact with prohibitins 1 and 2, proteins implicated in c-Raf-MEK-ERK signaling. Because increased ERK signaling stimulates eIF4E phosphorylation status, rocaglates are also expected to inhibit eIF4E phosphorylation status, a point that has not been thoroughly investigated. It is currently unknown whether the effects on translation observed with rocaglates are solely through eIF4A inhibition or also a feature of blocking eIF4E phosphorylation. Here, we show that rocaglates inhibit translation through an eIF4E phosphorylation-independent mechanism.P50 GM067041 - NIGMS NIH HHS; R01 GM073855 - NIGMS NIH HHS; GM-067041 - NIGMS NIH HHS; MOP-106530 - Canadian Institutes of Health Researc

Diastereodivergent synthesis of chiral tetrahydropyrrolodiazepinediones via a one-pot intramolecular aza-Michael/lactamization sequence

A modular and diastereodivergent synthesis of tetrahydro-1H-pyrrolo[1,2d]diazepine-(2,5)-diones is presented. The tetrahydropyrrolodiazepinedione scaffold is obtained via a base-mediated three-step isomerization/tandem cyclization of amino acid-coupled homoallylic amino esters. Diastereoselectivity of the process is mediated by the interplay of a kinetic cyclization event and a propensity for thermodynamic epimerization at two labile chiral centers, giving rise to two distinct major diastereomers dependent on starting material stereochemistry and reaction conditions selected. Herein, we present a synthetic and computational study for this tandem process on a variety of amino ester substrates.Work at the BU-CMD is supported by R24GM111625. The authors wish to thank Dr. Jeffrey Bacon for assistance with Xray crystallographic analysis, Dr. Norman Lee for assistance with high-resolution mass spectrometry analysis, and Dr. Paul Ralifo for assistance with NMR analysis. NMR (CHE-0619339) and MS (CHE-0443618) facilities at Boston University are supported by the NSF. (CHE-0619339 - NSF; CHE-0443618 - NSF; R24GM111625)Published versionSupporting documentationAccepted manuscrip

Synthesis of aza-rocaglates via ESIPT-mediated (3+2) photocycloaddition

Synthesis of aza-rocaglates, nitrogen-containing analogues of the rocaglate natural products, is reported. The route features ESIPT-mediated (3+2) photocycloaddition of 1-alkyl-2-aryl-3-hydroxyquinolinones with the dipolarophile methyl cinnamate. A continuous photoflow reactor was utilized for photocycloadditions. An array of compounds bearing the hexahydrocyclopenta[b]indole core structure was synthesized and evaluated in translation inhibition assays.R01 CA175744 - NCI NIH HHS; R01 GM073855 - NIGMS NIH HHS; R24 GM111625 - NIGMS NIH HHS; R35 GM118173 - NIGMS NIH HH

Remodelling of the natural product fumagillol employing a reaction discovery approach

In the search for new biologically active molecules, diversity-oriented synthetic strategies break through the limitation of traditional library synthesis by sampling new chemical space. Many natural products can be regarded as intriguing starting points for diversity-oriented synthesis, wherein stereochemically rich core structures may be reorganized into chemotypes that are distinctly different from the parent structure. Ideally, to be suited to library applications, such transformations should be general and involve few steps. With this objective in mind, the highly oxygenated natural product fumagillol has been successfully remodelled in several ways using a reaction-discovery-based approach. In reactions with amines, excellent regiocontrol in a bis-epoxide opening/cyclization sequence can be obtained by size-dependent interaction of an appropriate catalyst with the parent molecule, forming either perhydroisoindole or perhydroisoquinoline products. Perhydroisoindoles can be further remodelled by cascade processes to afford either morpholinone or bridged 4,1-benzoxazepine-containing structures.P50 GM067041 - NIGMS NIH HHS; P50 GM067041-07 - NIGMS NIH HHS; P50 GM067041-08 - NIGMS NIH HHS; P50 GM067041-09 - NIGMS NIH HH

Targeting the eIF4A RNA helicase blocks translation of the MUC1-C oncoprotein

The oncogenic MUC1-C subunit is aberrantly overexpressed in most human breast cancers by mechanisms that are not well understood. The present studies demonstrate that stimulation of non- malignant MCF-10A cells with epidermal growth factor (EGF) or heregulin (HRG) results in marked upregulation of MUC1-C translation. Growth factor-induced MUC1-C translation was found to be mediated by PI3K->AKT, and not MEK->ERK1/2, signaling. We also show that activation of the mTORC1->S6K1 pathway decreases PDCD4, an inhibitor of the eIF4A RNA helicase, and contributes to the induction of MUC1-C translation. In concert with these results, treatment of growth factor-stimulated MCF-10A cells with the eIF4A RNA helicase inhibitors, silvestrol and CR-1-31-B, blocked increases in MUC1-C abundance. The functional significance of the increase in MUC1-C translation is supported by the demonstration that MUC1-C, in turn, forms complexes with EGFR and promotes EGFR-mediated activation of the PI3K->AKT pathway and the induction of growth. Compared to MCF-10A cells, constitutive overexpression of MUC1-C in breast cancer cells was unaffected by EGF stimulation, but was blocked by inhibiting PI3K->AKT signaling. The overexpression of MUC1-C in breast cancer cells was also inhibited by blocking eIF4A RNA helicase activity with silvestrol and CR-1-31-B. These findings indicate that EGF-induced MUC1-C expression is mediated by the PI3K->AKT pathway and the eIF4A RNA helicase, and that this response promotes EGFR signaling in an autoinductive loop. The findings also indicate that targeting the eIF4A RNA helicase is a novel approach for blocking MUC1-C overexpression in breast cancer cells.P50 CA100707 - NCI NIH HHS; R01 CA042802 - NCI NIH HHS; R01 CA097098 - NCI NIH HHS; R01 GM073855 - NIGMS NIH HH

Inhibition of oncogenic transcription factor REL by the natural product derivative calafianin monomer 101 induces proliferation arrest and apoptosis in human B-lymphoma cell lines

Increased activity of transcription factor NF-κB has been implicated in many B-cell lymphomas. We investigated effects of synthetic compound calafianin monomer (CM101) on biochemical and biological properties of NF-κB. In human 293 cells, CM101 selectively inhibited DNA binding by overexpressed NF-κB subunits REL (human c-Rel) and p65 as compared to NF-κB p50, and inhibition of REL and p65 DNA binding by CM101 required a conserved cysteine residue. CM101 also inhibited DNA binding by REL in human B-lymphoma cell lines, and the sensitivity of several B-lymphoma cell lines to CM101-induced proliferation arrest and apoptosis correlated with levels of cellular and nuclear REL. CM101 treatment induced both phosphorylation and decreased expression of anti-apoptotic protein Bcl-XL, a REL target gene product, in sensitive B-lymphoma cell lines. Ectopic expression of Bcl-XL protected SUDHL-2 B-lymphoma cells against CM101-induced apoptosis, and overexpression of a transforming mutant of REL decreased the sensitivity of BJAB B-lymphoma cells to CM101-induced apoptosis. Lipopolysaccharide-induced activation of NF-κB signaling upstream components occurred in RAW264.7 macrophages at CM101 concentrations that blocked NF-κB DNA binding. Direct inhibitors of REL may be useful for treating B-cell lymphomas in which REL is active, and may inhibit B-lymphoma cell growth at doses that do not affect some immune-related responses in normal cells.R01 GM094551 - NIGMS NIH HHS; P50 GM067041 - NIGMS NIH HHS; GM094551 - NIGMS NIH HHS; R24 GM111625 - NIGMS NIH HHS; GM067041 - NIGMS NIH HH

How proteins bind macrocycles

The potential utility of synthetic macrocycles (MCs) as drugs, particularly against low-druggability targets such as protein-protein interactions, has been widely discussed. There is little information, however, to guide the design of MCs for good target protein-binding activity or bioavailability. To address this knowledge gap, we analyze the binding modes of a representative set of MC-protein complexes. The results, combined with consideration of the physicochemical properties of approved macrocyclic drugs, allow us to propose specific guidelines for the design of synthetic MC libraries with structural and physicochemical features likely to favor strong binding to protein targets as well as good bioavailability. We additionally provide evidence that large, natural product-derived MCs can bind targets that are not druggable by conventional, drug-like compounds, supporting the notion that natural product-inspired synthetic MCs can expand the number of proteins that are druggable by synthetic small molecules.R01 GM094551 - NIGMS NIH HHS; GM064700 - NIGMS NIH HHS; GM094551 - NIGMS NIH HHS; R01 GM064700 - NIGMS NIH HHS; GM094551-01S1 - NIGMS NIH HH