Hyperstable alkenes: are they remarkably unreactive?

In 1981, Maier and Schleyer first identified a select number of cage bicyclic olefins (alkenes) as "hyperstable", and predicted them to be "remarkably unreactive", based solely on theoretical methods. Since that time only three systems meeting the criteria of a hyperstable alkene have been reported in the literature. A one-pot, telescoped synthesis, of four hyperstable alkenes is reported herein, which has uncovered unexpected reactivity towards oxidation.

Reassignment of the Structure of a Tryptophan-Containing Cyclic Tripeptide Produced by the Biarylitide Crosslinking Cytochrome P450.

The structure of the sidechain crosslinked Tyr-Leu-Trp peptide produced by the biarylitide crosslinking cytochrome P450 from Micromonospora sp. MW-13 has been reanalysed by a series of NMR, computational and isotope labelling experiments and shown to contain a C-N rather than a C-O bond. Additional in vivo experiments using such a modified peptide show there is a general tolerance of biarylitide crosslinking P450 enzymes for histidine to tryptophan mutations within their minimal peptide substrate sequences despite the lack of such residues noted in natural biarylitide gene clusters.

The (±)-5-Aza[1.0]triblattane Skeleton via Azetine Cycloaddition.

The first synthesis of the 5-aza[1.0]triblattane skeleton was achieved through a [4 + 2] cycloaddition approach using a suitably protected azetine and cyclopentadiene. A series of azetines were synthesized to explore both stability and suitable N-protection.

-1-Azacubane-2-carboxylic Acid: Derivative Scope and Comparative Biological Evaluation.

The unusual and sterically constrained amino acid, -1-azacubane-2-carboxylic acid, was incorporated into a range of bioactive chemical templates, including enalaprilat, perindoprilat, endomorphin-2 and isoniazid, and subjected to biological testing. The endomorphin-2 derivative displayed increased activity at the δ opioid receptor, but a loss in activity was observed in the other cases, although human normal cell line evaluation suggests limited cytotoxic effects.

Isolation and In Vitro and In Vivo Activity of Secondary Metabolites from Baker against Malaria Parasites.

Chemical investigation of the antimalarial medicinal plant led to the isolation of five new diterpenoids, including ajugarins VII-X (-) and teuvincenone K (), along with four known compounds, namely, 12,16-epoxy-6,11,14,17-tetrahydroxy-17(15 → 16)--5,8,11,13,15-abietapentaen-7-one (), methyl pheophorbide A (), loliolide (), and acacetin (). The chemical structures of the new compounds were elucidated using NMR spectroscopy, mass spectrometry, circular dichroism, as well as density functional theory calculations. All compounds were evaluated for activity against 3D7 malaria parasites with methyl pheophorbide A () showing the strongest activity (IC 4.

9-Azahomocubane.

Homocubane, a highly strained cage hydrocarbon, contains two very different positions for the introduction of a nitrogen atom into the skeleton, e. g., a position 1 exchange results in a tertiary amine whereas position 9 yields a secondary amine.

-1-Azacubane-2-carboxylic acid-Amide Bond Comparison to Proline.

-1-Azacubane-2-carboxylic acid, an unusual and sterically constrained amino acid, was found to undergo amide bond formation at both the N- and C-termini using proline based bioactive molecule templates as a concept platform.

Stretching Peptides to Generate Small Molecule β-Strand Mimics.

Advances in the modulation of protein-protein interactions (PPIs) enable both characterization of PPI networks that govern diseases and design of therapeutics and probes. The shallow protein surfaces that dominate PPIs are challenging to target using standard methods, and approaches for accessing extended backbone structures are limited. Here, we incorporate a rigid, linear, diyne brace between side chains at the to 2 positions to generate a family of low-molecular-weight, extended-backbone peptide macrocycles.

1-Azahomocubane.

Highly strained cage hydrocarbons have long stood as fundamental molecules to explore the limits of chemical stability and reactivity, probe physical properties, and more recently as bioactive molecules and in materials discovery. Interestingly, the nitrogenous congeners have attracted much less attention. Previously absent from the literature, azahomocubanes, offer an opportunity to investigate the effects of a nitrogen atom when incorporated into a highly constrained polycyclic environment.

Meeting the Challenge 2: Identification of Potential Chemical Probes for Parkinson's Disease from Hort Using Cytological Profiling.

Traditional Chinese medicine (TCM) has been around for thousands of years and is increasingly gaining popularity in the Western world to treat various complex disorders including the incurable neurodegenerative condition, Parkinson's Disease (PD). One of the many directions in recent studies of PD is utilizing the phenotypic assay, or cytological profiling, to evaluate the phenotypic changes of PD-implicated cellular components in patient-derived olfactory neuroepithelial (hONS) cells, upon treating the cells with extracts or pure compounds. To obtain small molecules for studies utilizing PD phenotyping assays, Hort was selected for analysis as it is a popular Chinese herbal medicine used for treating PD-like symptoms.

A New Metric for Evaluating DFT Calculated Proton and Carbon Chemical Shifts of Natural Products and Organic Compounds.

The calculation of DFT (density functional theory) chemical shifts have become an important technique for the verification of a proposed structure. An easily calculated metric developed for proton and carbon chemical shifts of natural products and organic compounds, the calculated chemical shift index (CCSI), has been developed, which uses the deviation of each pair of calculated and experimental chemical shifts. The mean absolute deviation (MAD), which is commonly used as the goodness of fit metric for DFT calculated chemical shifts, can conceal large deviations in the calculated data.

Synthesis, isolation and characterisation of fluorinated-benzimidazoisoquinoline regioisomers.

A pair of novel fluorinated-benzimidazoisoquinoline regioisomers was synthesised and isolated. Initial structural characterisation and identification employed 1D proton, 1D carbon, correlated spectroscopy (COSY), heteronuclear single quantum coherence (HSQC), and heteronuclear multiple bond correlation (HMBC) nuclear magnetic resonance spectroscopy and mass spectrometry. However, the fluorinated regioisomers could not be differentiated using nuclear magnetic resonance (NMR) alone.

Austrobuxusin N, a new picrotoxane terpenoid glycoside, from the Australian endemic plant (Beuzev. & C.T. White) Airy Shaw.

A new picrotoxane terpenoid glycoside, austrobuxusin N (), together with four known compounds, austrobuxusin A-D (-), were isolated from the leaves of the Australian endemic plant (Beuzev. & C.T.

Chemical constituents from Macleaya cordata (Willd) R. Br. and their phenotypic functions against a Parkinson's disease patient-derived cell line.

Cytological profiling (CP) assay against a human olfactory neuroshpere-derived (hONS) cell line using a library of traditional Chinese medicinal plant extracts gave indications that the ethanolic extract of Macleaya cordata (Willd) R. Br. elicited strong perturbations to various cellular components.

Synthetic Tigliane Intermediates Engage Thiols to Induce Potent Cell Line Selective Anti-Cancer Activity.

The tigliane ring system, which encompasses iconic members such as phorbol and TPA, is widely renowned due to numerous observations of displaying potent biological activity, and subsequent use as mainstream biochemical tools. Traditionally, naturally occurring phorboids are regarded as tumor promotors through PKC activation, although in recent times more highly oxidized natural derivatives have been identified as anti-tumor agents. In the view that only limited synthetic investigations toward skeletal stereochemical modification have been undertaken, non-natural systems could be useful for a better understanding of the tigliane pharmacophore via interrogation of cellular sensitivity.

Dynamic NMR and Computational Studies Inform the Conformational Description of Dendrillane Terpenes from the Nudibranch .

Two new oxygenated terpenes ( and ) have been characterized from the Australian nudibranch . Broadened H NMR signals, together with the absence of individual carbon NMR signals, complicated analysis of 5,9-epoxydendrillolide A (); increasing the temperature to 323 K revealed the missing NMR signals. Low-temperature H NMR experiments provided an activation barrier of ∼15 kcal mol and, together with DFT calculations, supported interconversion of a twist chair conformer with two different chair conformers.

Radiolabeling of protected tryptophan with [F]fluoromethyl tosylate: Formation of [F]fluoromethyl ester of tryptophan instead of 1-N-[F]fluoromethyl tryptophan methylester.

The reaction of [F]fluoromethyl tosylate with methyl(tert-butoxycarbonyl)-l-tryptophanate results in formation the O-alkylated ester of the tryptophan instead of alkylation of the indole nitrogen of tryptophan as initially anticipated. Treatment of protected tryptophan with NaH in dimethyl formamide (DMF) along with [F]fluoromethyl tosylate at 130°C results in the formation of [F]fluoromethyl(tert-butoxycarbonyl)-l-tryptophanate. Preferential formation of the O-alkylated product is postulated to be due to the hydrolysis of the ester.

Enabling adoption of 2D-NMR for the higher order structure assessment of monoclonal antibody therapeutics.

The increased interest in using monoclonal antibodies (mAbs) as a platform for biopharmaceuticals has led to the need for new analytical techniques that can precisely assess physicochemical properties of these large and very complex drugs for the purpose of correctly identifying quality attributes (QA). One QA, higher order structure (HOS), is unique to biopharmaceuticals and essential for establishing consistency in biopharmaceutical manufacturing, detecting process-related variations from manufacturing changes and establishing comparability between biologic products. To address this measurement challenge, two-dimensional nuclear magnetic resonance spectroscopy (2D-NMR) methods were introduced that allow for the precise atomic-level comparison of the HOS between two proteins, including mAbs.

Elucidation of Relative and Absolute Configurations of Highly Rearranged Diterpenoids and Evidence for a Putative Biosynthetic Intermediate from the Australian Nudibranch Goniobranchus geometricus.

A diterpene (1), previously isolated from a Japanese marine sponge, together with two undescribed (2, 3) diterpenes with highly rearranged carbon skeletons have been characterized from the Australian nudibranch species Goniobranchus geometricus. The structures and relative configuration were determined by spectroscopic analyses informed by detailed molecular modeling, as well as by DFT, DP4, and coupling constant predictions. A 13 R,14 R configuration was determined for secoshahamin (1) by chemical correlation with 12-desacetoxyshahamin C (4) and 12-desacetoxypolyrhaphin A (5); each metabolite (1, 4, and 5) was subjected to saponification and lactonization, yielding the same δ-lactone product (6).

Cytotoxic Spiroepoxide Lactone and Its Putative Biosynthetic Precursor from .

Epoxygoniolide-1 (), possessing spiroepoxide lactone, enal, and masked dialdehyde functionalities, has been characterized from the conspicuously patterned mollusc . Its relative configuration was investigated by spectroscopic analyses, molecular modeling, and density functional theory calculations. The biosynthesis of may involve rearrangement of a diterpene framework, providing a precursor to cometabolite gonioline (), followed by C-C bond cleavage (via Grob or P450 mechanism).

N-(4-[F]fluorobenzyl)cholylglycine, a novel tracer for PET of enterohepatic circulation of bile acids: Radiosynthesis and proof-of-concept studies in rats.

Introduction: Enterohepatic circulation (EHC) of conjugated bile acids is an important physiological process crucial for regulation of intracellular concentrations of bile acids and their function as detergents and signal carriers. Only few bile acid-derived imaging agents have been synthesized and hitherto none have been evaluated for studies of EHC. We hypothesized that N-(4-[F]fluorobenzyl)cholylglycine ([F]FBCGly), a novel fluorine-18 labeled derivative of endogenous cholylglycine, would be a suitable tracer for PET of the EHC of conjugated bile acids, and we report here a radiosynthesis of [F]FBCGly and a proof-of-concept study by PET/MR in rats.

Structural insights into the mechanism of inhibition of AHAS by herbicides.

Acetohydroxyacid synthase (AHAS), the first enzyme in the branched amino acid biosynthesis pathway, is present only in plants and microorganisms, and it is the target of >50 commercial herbicides. Penoxsulam (PS), which is a highly effective broad-spectrum AHAS-inhibiting herbicide, is used extensively to control weed growth in rice crops. However, the molecular basis for its inhibition of AHAS is poorly understood.

Antitubercular and Cytotoxic Chlorinated seco-Cyclohexenes from Uvaria alba.

Two new chlorine-containing polyoxygenated seco-cyclohexenes, albanols A (1) and B (2), along with the oxepinone metabolite grandiuvarone (3) were isolated from the endemic Philippine Annonaceae plant Uvaria alba. Both new compounds exhibited modest antitubercular activity. Compound 1 showed cytostatic activity (ranging from 1-50 μM) against HeLa cells and weak antiproliferative activity against HUVEC and K-562 cells with GI values of 106 and 81 μM, respectively.

Design of Plasmodium vivax Hypoxanthine-Guanine Phosphoribosyltransferase Inhibitors as Potential Antimalarial Therapeutics.

Plasmodium falciparum (Pf) and Plasmodium vivax (Pv) are the foremost causative agents of malaria. Due to the development of resistance to current antimalarial medications, new drugs for this parasitic disease need to be discovered. The activity of hypoxanthine-guanine-[xanthine]-phosphoribosyltransferase, HG[X]PRT, is reported to be essential for the growth of both of these parasites, making it an excellent target for antimalarial drug discovery.