Multicyclic Structures Research Articles

Mechanochemistry of Pterodactylane.

Pterodactylane is a [4]-ladderane with substituents on the central rung. Comparing the mechanochemistry of the [4]-ladderane structure when pulled from the central rung versus the end rung revealed a striking difference in the threshold force of mechanoactivation: the threshold force is dramatically lowered from 1.9 nN when pulled on the end rung to 0.7 nN when pulled on the central rung. We investigated the bicyclic products formed from the mechanochemical activation of pterodactylane experimentally and computationally, which are distinct from the mechanochemical products of ladderanes being activated from the end rung. We compared the products of pterodactylane's mechanochemical and thermal activation to reveal differences and similarities in the mechanochemical and thermal pathways of pterodactylane transformation. Interestingly, we also discovered the presence of elementary steps that are accelerated or suppressed by force within the same mechanochemical reaction of pterodactylane, suggesting rich mechanochemical manifolds of multicyclic structures. We rationalized the greatly enhanced mechanochemical reactivity of the central rung of pterodactylane and discovered force-free ground state bond length to be a good low-cost predictor of the threshold force for cyclobutane-based mechanophores. These findings advance our understanding of mechanochemical reactivities and pathways, and they will guide future designs of mechanophores with low threshold forces to facilitate their applications in force-responsive materials.

Chemoselective Hydrogenation of Ring‐Strained Monoterpenes: A Route to High‐Performance Sustainable Aviation Fuels

Two novel hydrocarbon fuels derived from bio-based monoterpene feedstocks by chemoselective hydrogenation are prepared. The ring-strained, multicyclic structures of these molecules result in higher energy densities and lower viscosities compared to conventional jet fuel. Generation of the starting monoterpenes via fermentation of biomass sugars will enable the sustainable production of high-performance aviation fuels. More details can be found in article number 2100221, Josanne-Dee Woodroffe, Benjamin G. Harvey.

Fused Dihydrodibenzobarrelene (Dibenzobicylco[2.2.2]octadiene) and Lactone Rings via Tandem Diels‐Alder and Condensation Reactions of Dialkyl Fumarates and 9‐Anthracenemethanol

AbstractA series of fused dihydrodibenzobarrelene (dibenzobicyclo[2.2.2]octadiene) and lactone rings were prepared from dialkyl fumarates and 9‐anthracenemethanol. These products were prepared via a one‐pot synthesis in which a Diels‐Alder reaction occurred followed by an intramolecular transesterification to form the lactone ring. A key feature of this synthetic methodology is the straightforward purification of the reaction products, in most cases without the need for chromatography. The ease of work‐up along with the simple setup of the reaction (no catalysts or other reagents needed) make this methodology a convenient and potentially scalable route to complex, multicyclic structures. Molecular modeling of the transition structures for Diels‐Alder reaction suggested that transesterification could precede cycloaddition, but NMR in situ studies confirmed the opposite occurrence. Product formed exclusively in the trans configuration for all alkyl fumarates used.

Biosourced Cyclic and Multicyclic Polyesters Based on 1,4:3,6-Dianhydrohexitols: Application to Metal Ions Uptake in Aqueous Media

Isosorbide and isomannide are polycondensed in solution with trimesoyl chloride at a concentration of 0.06 mol L−1 for the synthesis of cyclic and multicyclic polyesters. The feed ratio diol/trimesoyl chloride is varied from 1.0/1.0 to 1.6/1.0. As all obtained polyesters prove insoluble, innovative solvent-free matrix assisted laser desorption ionization time-of-flight mass spectrometry (MALDI ToF MS) is performed for their characterization. The influence of the stereochemistry is shown to be of great importance for the cyclization trend. Both isosorbide and isomannide lead mainly to cyclic and multicyclic structures at a feed ratio of 1.0/1.0 and 1.1/1.0. Isomannide gives higher fractions of multicyclic structures. The products are characterized by complementary techniques such as 13C cross polarization magic angle spinning nuclear magnetic resonance (13C CP-MAS NMR) and differential scanning calorimetry measurements. Application as a cryptands for the uptake of metal ions in aqueous media is followed by inductively coupled plasma atomic emission spectroscopy (ICP AES) analysis and reveal efficient toward large range of metals with tunable selectivity depending on the starting diol.

Enantioselective Intramolecular Formal [2 + 4] Annulation of Acrylates and α,β-Unsaturated Imines Catalyzed by Amino Acid Derived Phosphines

The first chiral phosphine-catalyzed activation of acrylates for intramolecular formal [2 + 4] reactions with unsaturated imines is described. The catalytic reactions afford N-heterocycles with exceptionally high diastereo- and enantioselectivities. The [2 + 4] products are amenable for further transformations to useful molecules such as chiral piperidines and multicyclic structures.

Divergolides A–D from a Mangrove Endophyte Reveal an Unparalleled Plasticity in ansa‐Macrolide Biosynthesis

In-built diversification: Four ansa macrolides, divergolides A–D (1–4), with intriguing structures were isolated from a bacterial endophyte of the mangrove tree Bruguiera gymnorrhiza. These compounds are generated by a common biogenesis from a linear precursor that undergoes various reactions to give the multicyclic structures. This remarkable plasticity results in metabolites with different antibacterial and cytotoxic properties. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Characteristics Of The GC-MS Mass Spectra Of Terpenoids (C10H16)

The terpenoids, sometimes referred to as isoprenoids, are a large and diverse class of naturally occurring organic chemicals similar to terpenes, derived from five-carbon isoprene units assembled and modified in thousands of ways. Most are multicyclic structures that differ from one another not only in functional groups, but also in their basic carbon skeletons. These lipids can be found in all classes of living things, and are the largest group of natural products. The features of mass spectra of mono-, bi- and tri-cyclic terpenoids: 1-isopropyl-4-methyl-1, 3-cyclohexadiene (I) terpilene; 1-methyl-4-(1-methylethylidene)-1- cyclohexene (II) terpinolene; 4-methyl-3-(1-methylethylidene)-1-cyclohexene (III); 1,5,5-trimethyl 3-methylene-1-cyclohexene (IV); 2,6,6-trimethylbicyclo\\\\\\\\\\\\\\ [3.1.1]-2-heptene (V) ii -pinene; 2,2,6-trimethylbicyclo [3.1.1]-2-heptene (VI) i¢ -pinene; 2,2-dimethyl-3-methylenebicyclo [2.2.1]-heptane (VII) camphene;1-isopropyl-4-methylbicyclo [3.1.0]-2-hexene (VIII) i¢ -thugene; 5-isopropyl-2-methylbicyclo [3.1.0]-2-hexene (IX) ii -thugene; 1-methyl-6-(1-methylidene) bicycle [3.1.0] hexane (X); 3,7,7-trimethylbicyclo [4.1.0]-3-heptene (XI) i¤ -3-carene; 4,7,7-trimethylbicyclo [4.1.0]-2-heptene (XII) (+)-4-carene; 3,7,7- trimethylbicyclo [4.1.0]-2-heptene (XIII) (+)-2-carene; 1,7,7-trimethyltricyclo [2.2.1.0(2.6)]-heptane (XVI) tricyclene; 1,3,3-trimethyltricyclo [2.2.1.0(2.6)]- heptane (XVII) cyclofenchene extracted from natural raw materials and comprising a number of drugs were investigated. The mass spectra for: cyclohexene- 3-(tretbutyl) peroxide (XIV) and 3-isopropyl-1-cyclohexene (XV) were investigated as well. It was established that the mass spectra of these compounds are absolutely identical in mass values of peaks of fragment ions, where their relative intensities have minor differences. In the spectra of all compounds the observed characteristic ions were [M-CH (CH3)2] and [M-CH (CH3)2 –H2]. The latter has a structure with m/z 91 that is attributed to pathing. All fragment ions correspond to even-electron cations. The identity of mass spectra of the studied tepenoids is explained by isomerization of molecular ions, similar to isomerization of terpenes in chemical transformations under the action of acids, also under the influence of other catalysts, temperature and light

The Synthesis and Study of Side‐Chain Lactam‐Bridged Peptides

AbstractFor Abstract see ChemInform Abstract in Full Text.

A Remarkable Cycloadditionof Bis(arylsulfonyl)iodonium Ylide with Norbornene Derivativesfor the Direct Synthesis of Functionalized Indanes

The reaction of bis(arylsulfonyl)iodonium ylides with a variety of norbornene derivatives 3 affords functionalized indanes 4 in good yields through an unusual cycloaddition. This diastereoselective cycloaddition provides a convenient preparative route to multicyclic structures of well defined stereochemical configuration.

The synthesis and study of side-chain lactam-bridged peptides.

Side-chain lactam bridges linking amino acid residues that are spaced several residues apart in the linear sequence offer a convenient and flexible method for introducing conformational constraints into a peptide structure. The availability of a variety of selectively cleavable protecting groups for amines and carboxylic acids allows for several approaches to the synthesis of monocyclic, dicyclic, and bicyclic lactam-bridged peptides by solid-phase methods. Multicyclic structures are also accessible, but segment-condensation syntheses with solution-phase cyclizations are most likely to provide the best synthetic approach to these more complex constrained peptides. Lactam bridges linking (i, i + 3)-, (i, i + 4), and (i, i + 7)-spaced residue pairs have all proven useful for stabilization of alpha helices, and (i, i + 3)-linked residues have also been demonstrated to stabilize beta-turns. These structures are finding an increasing number of applications in protein biology, including studies of protein folding, protein aggregation, peptide ligand-receptor recognition, and the development of more potent peptide therapeutics. Defining the functional roles of the amphiphilic alpha-helices in medium-sized peptide hormones, and studying helix propagation from rigid, alpha-helix initiating bicyclic peptides are among the most exciting developments currently underway in this field.

Coexistence of Neutral and Ion-Pair Clusters of Hydrated Sulfuric Acid H2SO4(H2O)n (n = 1−5)A Molecular Orbital Study

Various isomeric structures of the hydrated clusters of sulfuric acid, H2SO4(H2O)n (n = 1−5), are examined using a density functional molecular orbital method. Due to the small energy difference between trans and cis conformations about two OH groups of sulfuric acid, there are three types of isomeric forms of the hydrated clusters of sulfuric acid which involve the proton nontransferred trans conformer, the proton transferred trans conformer, and the proton nontransferred cis conformer of sulfuric acid. In the case of transoid H2SO4, the proton transferred ion-pair structures become more stable than the proton nontransferred structures as the number of water molecules increases. The hydrated clusters of the cis conformation remain neutral hydrogen-bonded structures even if the number of water molecules increases. All stable clusters tend to form multi-cyclic structures. While both protons of sulfuric acid participate in cyclic hydrogen bonding in the neutral structures, the OH group of HSO4- in the ion-p...

Effects of Estrogenic Xenobiotics on Molting of the Water Flea,Daphnia magna

The effects of five xenobiotics, 2,4,5-trichloribiphenyl (PCB29), the polychlorinated biphenyl (PCB) Aroclor 1242, diethyl phthalate, lindane, and 4-octylphenol, on molting ofDaphnia magnawere investigated. All except PCB29 are known to have unexpected estrogenicity in vertebrates. Daphnids exposed to PCB29, Aroclor 1242, and diethyl phthalate took significantly more time to complete four molts than did the controls. The inhibitory effects of theseortho-chlorinated PCBs suggest that certain structural features, most probably includingortho-chlorination, are related to the ability of a PCB to affect molting. Agents with multicyclic structures, such as PCBs, are more effective in inhibiting molting than are single-ringed xenobiotics, such as diethyl phthalate, which suggests that hydrophobicity may be a requirement for binding to the ecdysteroid receptor. These molt-inhibiting agents with multiple rings appear to bear more structural resemblance to the steroidal molting hormones of arthropods, the ecdysteroids, than do the single-ringed ones. While the possibility of alternative mechanisms, such as impairment of ecdysteroidogenesis exists, the results obtained herein support the hypothesis that some xenobiotics which disrupt endocrine processes in vertebrates can also interfere with the hormonally regulated molting process in arthropods through acting as antagonists of endogenous ecdysteroids by binding to and thereby blocking the ecdysteroid receptor.

Synthesis, conformational analysis, and antimalarial activity of tricyclic analogs of artemisinin

Aspects of synthesis, conformational analysis, and antimalarial activity of artemisinin analogs (±)-5-nor-6-desmethyl-4,5-secoartemisinin ( 2), (−)-5-nor-4,5-secoartemisinin ( 3), (+)-4,5-secoartemisinin ( 4), and (+)-4,5-desethano-artemisinin ( 5) 22 are described. The conformations of these multicyclic structures were determined through a combination of X-ray crystallography, NMR, and computational analysis, with an emphasis on the 1,2,4-trioxane geometry. Two major solution conformations for both 2 and 3 were found: all chair forms 2a and 3a, and twist-boat/twist-boat/chair forms 2b and 3b, respectively. The major solution conformer 2a matched the solid state structure found via X-ray crystallography. Computations suggest that (+)-4,5-Secoartemisinin ( 4) has three conformations of equal energy: chair/twist-boat, 4a, twist-boat/twist-boat/chair, 4b, corresponding to the X-ray crystal structure, and twist boat/chair/chair, 4c. The 1,2,4-trioxane and lactone rings adopt the twist-boat conformations in 2b, 3b, 4a, and 4c. When compared to artemisinin, these tricyclic, flexible analogs have different geometry yet retain some in vitro antimalarial activity against resistant strains of Plasmodium falciparum. Possible structure/activity correlations are discussed.