A detailed account of the development of a general strategy for synthesis of the C-19 methyl-substituted alkaloids including total synthesis of 19(S),20(R)-dihydroperaksine-17-al (1), ...19(S),20(R)-dihydroperaksine (2), and peraksine (6) is presented. Efforts directed toward the total synthesis of macrosalhine chloride (5) are also reported. Important to success is the sequence of chemical reactions which include a critical haloboration reaction, regioselective hydroboration, and controlled oxidation (to provide sensitive enolizable aldehydes at C-20). In addition, the all-important Pd-catalyzed α-vinylation reaction has been extended to a chiral C-19 alkyl-substituted substrate for the first time. Synthesis of the advanced intermediate 64 completes an improved formal total synthesis of talcarpine (26) and provides a starting point for synthesis of macroline-related alkaloids 27–31. Similarly, extension of this synthetic strategy in the ring A oxygenated series should provide easy access to the northern hemisphere 32b of the bisindoles angustricraline, alstocraline, and foliacraline (Figure ).
In our continuing effort to develop effective anti-heroin vaccines as potential medications for the treatment of opioid use disorder, herein we present the design and synthesis of the haptens: ...1-AmidoMorHap (
), 1-AmidoMorHap epimer (
), 1 Amido-DihydroMorHap (
), and 1 Amido-DihydroMorHap epimer (
). This is the first report of hydrolytically stable haptenic surrogates of heroin with the attachment site at the C1 position in the 4,5-epoxymorophinan nucleus. We prepared respective tetanus toxoid (TT)-hapten conjugates as heroin vaccine immunogens and evaluated their efficacy in vivo. We showed that all TT-hapten conjugates induced high antibody endpoint titers against the targets but only haptens
and
can induce protective effects against heroin in vivo. The epimeric analogues of these haptens,
and
, failed to protect mice from the effects of heroin. We also showed that the in vivo efficacy is consistent with the results of the in vitro drug sequestration assay. Attachment of the linker at the C1 position induced antibodies with weak binding to the target drugs. Only TT-
and TT-
yielded antibodies that bound heroin and 6-acetyl morphine. None of the TT-hapten conjugates induced antibodies that cross-reacted with morphine, methadone, naloxone, or naltrexone, and only TT-
interacted weakly with buprenorphine, and that subtle structural difference, especially at the C6 position, can vastly alter the specificity of the induced antibodies. This study is an important contribution in the field of vaccine development against small-molecule targets, providing proof that the chirality at C6 in these epoxymorphinans is a vital key to their effectiveness.
Quantum dots (QDs) are loaded with a series of peptides and proteins of increasing size, including a <20 residue peptide, myoglobin, mCherry, and maltose binding protein, which together cover a range ...of masses from <2.2 to ≈44 kDa. Conjugation to the surface of dihydrolipoic acid‐functionalized QDs is facilitated by polyhistidine metal affinity coordination. Increasing ratios of dye‐labeled peptides and proteins are self‐assembled to the QDs and then the bioconjugates are separated and analyzed using agarose gel electrophoresis. Fluorescent visualization of both conjugated and unbound species allows determination of an experimentally derived maximum loading number. Molecular modeling utilizing crystallographic coordinates or space‐filling structures of the peptides and proteins also allow the predicted maximum loadings to the QDs to be estimated. Comparison of the two sets of results provides insight into the nature of the QD surface and reflects the important role played by the nanoparticle's hydrophilic solubilizing surface ligands. It is found that for the larger protein molecules steric hindrance is the major packing constraint. In contrast, for the smaller peptides, the number of available QD binding sites is the principal determinant. These results can contribute towards an overall understanding of how to engineer designer bioconjugates for both QDs and other nanoparticle materials.
Quantum dots (QDs) are loaded with a series of peptides and proteins of increasing size including a <20 residue peptide, myoglobin, mCherry, and maltose binding protein, which cover a range of masses from <2.2 to ≈44 kD. These data provide insight into the QD surface, binding capacity, and the role played by the nanoparticle's surface solubilizing ligands.
The development of an efficient diastereoselective method that permits rapid construction of the tetracyclic core 17 of the Strychnos-Aspidosperma alkaloids is described. Enaminone 16, synthesized in ...high yield, has been cyclized under the influence of a Brønsted acid to provide the core tetracyclic framework 17 of the Strychnos alkaloids in optically active form or alternatively to the β-ketoester tetrahydro-β-carboline (THBC) unit 18, by varying the equivalents of acid and the molar concentration. Attempts to utilize 18 to form the C(7)–C(16) bond of the akuammiline related alkaloids represented by strictamine (22), using metal-carbenoid chemistry, are also described.
A field demonstration and longevity assessment for long-term monitoring of the explosive 2,4,6-trinitrotoluene (TNT) in a marine environment using an anti-TNT microfluidic immunosensor is described. ...The TNT immunosensor is comprised of a microfluidic device with 39 parallel microchannels (2.5 cm × 250 µm × 500 µm, L × W × D) fabricated in poly(methylmethacrylate) (PMMA), then chemically functionalized with antibodies possessing a high affinity for TNT. Synthesized fluorescence reporter complexes used in a displacement-based assay format were used for TNT identification. For field deployment the TNT immunosensor was configured onto a submersible moored steel frame along with frame controller, pumps and TNT plume generator and deployed pier side for intermittent plume sampling of TNT (1h increments). Under varying current and tidal conditions trace levels of TNT in natural seawater were detected over an extended period (>18 h). Overnight operation and data recording was monitored via a web interface.
Small-molecule inhibitors that block the MDM2-p53 protein–protein interaction (MDM2 inhibitors) are being intensely pursued as a new therapeutic strategy for cancer treatment. We previously published ...a series of spirooxindole-containing compounds as a new class of MDM2 small-molecule inhibitors. We report herein a reversible ring-opening-cyclization reaction for some of these spirooxindoles, which affords four diastereomers from a single compound. Our biochemical binding data showed that the stereochemistry in this class of compounds has a major effect on their binding affinities to MDM2, with >100-fold difference between the most potent and the least potent stereoisomers. Our study has led to the identification of a set of highly potent MDM2 inhibitors with a stereochemistry that is different from that of our previously reported compounds. The most potent compound (MI-888) binds to MDM2 with a K i value of 0.44 nM and achieves complete and long-lasting tumor regression in an animal model of human cancer.
DNA-nanoparticle conjugates are important tools in nanobiotechnology. Knowing the orientation, function, and length of DNA on nanoparticle surfaces at low nanomolar concentrations under physiological ...conditions is therefore of great interest. Here, we investigate the conformation of a 31 nucleotides (nt) long DNA attached to a semiconductor quantum dot (QD) via Förster resonance energy transfer (FRET) from Tb-DNA probes hybridized to different positions on the QD-DNA. Precise Tb-to-QD distance determination from 7 to 14 nm along 26 nt of the peptide-appended QD-DNA was realized by time-resolved FRET spectroscopy. The FRET nanoruler measured linear single-stranded (ssDNA) and double-stranded (dsDNA) extensions of ∼0.15 and ∼0.31 nm per base, reflecting the different conformations. Comparison with biomolecular modeling confirmed the denser conformation of ssDNA and a possibly more flexible orientation on the QD surface, whereas the dsDNA was fully extended with radial orientation. The temporally distinct photoluminescence decays of the different DNA-FRET configurations were used for prototypical DNA hybridization assays that demonstrated the large potential for extended temporal multiplexing. The extensive experimental and theoretical analysis of 11 different distances/configurations of the same QD-DNA conjugate provided important information on DNA conformation on nanoparticle surfaces and will be an important benchmark for the development and optimization of DNA-nanobiosensors.
Virtual screening has become a major focus of bioactive small molecule lead identification, and reports of agonists and antagonists discovered via virtual methods are becoming more frequent. G ...protein-coupled receptors (GPCRs) are the one class of protein targets for which success with this approach has been limited. This is likely due to the paucity of detailed experimental information describing GPCR structure and the intrinsic function-associated structural flexibility of GPCRs which present major challenges in the application of receptor-based virtual screening. Here we describe an in silico methodology that diminishes the effects of structural uncertainty, allowing for more inclusive representation of a potential docking interaction with exogenous ligands. Using this approach, we screened one million compounds from a virtual database, and a diverse subgroup of 100 compounds was selected, leading to experimental identification of five structurally diverse antagonists of the thyrotropin-releasing hormone receptors (TRH-R1 and TRH-R2). The chirality of the most potent chemotype was demonstrated to be important in its binding affinity to TRH receptors; the most potent stereoisomer was noted to have a 13-fold selectivity for TRH-R1 over TRH-R2. A comprehensive mutational analysis of key amino acid residues that form the putative binding pocket of TRH receptors further verified the binding modality of these small molecule antagonists. The described virtual screening approach may prove applicable in the search for novel small molecule agonists and antagonists of other GPCRs.
Inhibition of the MDM2–p53 protein–protein interaction is being actively pursued as a new anticancer therapeutic strategy, and spiro-oxindoles have been designed as a class of potent and efficacious ...small-molecule inhibitors of this interaction (MDM2 inhibitors). Our previous study showed that some of our first-generation spiro-oxindoles undergo a reversible ring-opening-cyclization reaction that, from a single compound in protic solution, results in an equilibrium mixture of four diastereoisomers. By exploiting the ring-opening-cyclization reaction mechanism, we have designed and synthesized a series of second-generation spiro-oxindoles with symmetrical pyrrolidine C2 substitution. These compounds undergo a rapid and irreversible conversion to a single, stable diastereoisomer. Our study has yielded compound 31 (MI-1061), which binds to MDM2 with K i = 0.16 nM, shows excellent chemical stability, and achieves tumor regression in the SJSA-1 xenograft tumor model in mice.
Treatments for autoimmunity—diseases where the immune system mistakenly attacks self‐molecules—are not curative and leave patients immunocompromised. New studies aimed at more specific treatments ...reveal that development of inflammation or tolerance is influenced by the form in which self‐antigens are presented. Using a mouse model of multiple sclerosis (MS), it is shown for the first time that quantum dots (QDs) can be used to generate immunological tolerance by controlling the density of self‐antigen on QDs. These assemblies display dense arrangements of myelin self‐peptide associated with disease in MS, are uniform in size (<20 nm), and allow direct visualization in immune tissues. Peptide‐QDs rapidly concentrate in draining lymph nodes, colocalizing with macrophages expressing scavenger receptors involved in tolerance. Treatment with peptide‐QDs reduces disease incidence tenfold. Strikingly, the degree of tolerance—and the underlying expansion of regulatory T cells—correlates with the density of myelin molecules presented on QDs. A key discovery is that higher numbers of tolerogenic particles displaying lower levels of self‐peptide are more effective for inducing tolerance than fewer particles each displaying higher densities of peptide. QDs conjugated with self‐antigens can serve as a new platform to induce tolerance, while visualizing QD therapeutics in tolerogenic tissue domains.
Quantum dots decorated with myelin peptides induce tolerance in a mouse model of multiple sclerosis. These nanoscale constructs rapidly drain to lymph nodes—tissues that coordinate immune function. The degree of tolerance and the expansion of regulatory T cells capable of controlling disease directly correlate to the density of peptide ligand displayed on the quantum dots.
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