Synthesis of C-Unsubstituted 1,2-Diazetidines and Their Ring-Opening Reactions via Selective N-N Bond Cleavage.

C-Unsubstituted 1,2-diazetidines, a rarely studied type of four-membered heterocyclic compounds, were synthesized through an operationally simple intermolecular vicinal disubstitution reaction. 1,2-Diazetidine derivatives bearing various N-arylsulfonyl groups were readily accessed and studied by experimental and computed Raman spectra. The ring-opening reaction of the diazetidine was explored and resulted in the identification of a selective N-N bond cleavage with thiols as nucleophiles, which stereoselectively produced a new class of N-sulfenylimine derivatives with C-aminomethyl groups.

Bis-corannulenoanthracene: An Angularly Fused Pentacene as a Precursor for Barrelene-Tethered Receptors for Fullerenes.

Bis-corannulenoanthracene (C50H22, 5) was prepared by the Diels-Alder double cycloaddition of isocorannulenofuran with "bis-benzyne", followed by deoxygenation of the adducts. Despite the presence of a pentacene core, 5 is stable enough to be isolated and stored. A cycloaddition reaction of 5 with maleic anhydride produces 10 which exhibits strong affinity toward C60, as evidenced by (1)H NMR titration experiment.

Bis-corannulene Receptors for Fullerenes Based on Klärner's Tethers: Reaching the Affinity Limits.

Bis-corannulene receptors 4 and 5 with Klärner's tethers prepared by the Diels-Alder cycloaddition form inclusion complexes with C60 and C70, as evidenced by (1)H NMR titration. While 4 exhibits affinity toward fullerenes comparable to the previously reported corannulene-based receptors, 5 exceeds the performance of the former systems by ca. 2 orders of magnitude and, in addition, shows an enhanced preference for C70 over C60.

A 2:1 receptor/C60 complex as a nanosized universal joint.

Buckycatcher II, a C51 H24 hydrocarbon with two corannulene pincers on a dibenzonorbornadiene tether, exhibits an affinity toward C60 in organic solvents that is dramatically higher than the original buckycatcher C60 H28 and other corannulene-based molecular receptors for fullerenes. In addition to the formation of an usual 1:1 C60 @catcher inclusion complex, a trimeric C60 @(catcher)2 assembly is detected in solutions and in the solid state. X-ray structure determination reveals a remarkable "universal joint" solvent-free crystal arrangement of the trimer, with a single fullerene cage wrapped by four corannulene subunits of two cooperating catcher receptors.

Thermodynamics of host-guest interactions between fullerenes and a buckycatcher.

(1)H NMR and isothermal titration calorimetry (ITC) experiments were employed to obtain reliable thermodynamic data for the formation of the 1:1 inclusion complexes of fullerenes C(60) and C(70) with the buckycatcher (C(60)H(28)). NMR measurements were done in toluene-d8 and chlorobenzene-d5 at 288, 298, and 308 K, while the ITC titrations were performed in toluene, chlorobenzene, o-dichlorobenzene, anisole, and 1,1,2,2-tetrachloroethane at temperatures from 278 to 323 K. The association constants, K(a), obtained with both techniques are in very good agreement.

An unsolvated buckycatcher and its first dianion.

The X-ray crystallographic study of C60H28 consisting of two tethered corannulene bowls revealed a unique solid-state packing based on tight convex-concave π-π interactions. The controlled reduction of C60H28 resulted in the isolation and structural characterization of its dianion in the form of the rubidium salt that shows an entrapment of counterions by an anionic pincer.

Corannulene subunit acts as a diene in a cycloaddition reaction: synthesis of C80H32 corannulyne tetramer.

Distortion of six-membered rings in corannulene subunits of corannulyne (1,2-didehydrocorannulene) cyclotrimer activates the system for a cycloaddition reaction with another corannulyne unit. This unprecedented cycloaddition in which a corannulene fragment acts as a diene produces the largest oligomer of corannulyne reported to date. X-ray crystallography reveals the highly nonplanar structure of the tetramer which exhibits conformational and optical absorption properties very different from those of the cyclotrimer.

(E)-3,3',4,4',7,7',8,8'-Octa-methyl-2H,2'H-1,1'-bi(cyclo-penta-[fg]acenaphthyl-enyl-idene)-2,2',5,5',6,6'-hexa-one dichloro-methane monosolvate.

The title compound, C(36)H(24)O(6)·CH(2)Cl(2), is a dimer of two essentially planar (r.m.s.

Epirubicin-[Anti-HER2/] Synthesized with an Epirubicin-(C-)-EMCS Analog: Anti-Neoplastic Activity against Chemotherapeutic-Resistant SKBr-3 Mammary Carcinoma in Combination with Organic Selenium.

Purpose: Discover the anti-neoplastic efficacy of epirubicin-(C-imino)-[anti-HER2/neu] against chemotherapeutic-resistant SKBr-3 mammary carcinoma and delineate the capacity of selenium to enhance it's cytotoxic anti-neoplastic potency.

Methods: In molar excess, EMCH was combined with epirubicin to create a covalent epirubicin-(C-imino)-EMCH-maleimide intermediate with sulfhydryl-reactive properties. Monoclonal immunoglobulin selective for HER2/neu was then thiolated with 2-iminothiolane at the terminal ε-amine group of lysine residues.

Acid cleavable surface enhanced raman tagging for protein detection.

Dye conjugation is a common strategy improving the surface enhanced Raman detection sensitivity of biomolecules. Reported is a proof-of-concept study of a novel surface enhanced Raman spectroscopic tagging strategy termed as acid-cleavable SERS tag (ACST) method. Using Rhodamine B as the starting material, we prepared the first ACST prototype that consisted of, from the distal end, a SERS tag moiety (STM), an acid-cleavable linker, and a protein reactive moiety.

Sensitive carbohydrate detection using surface enhanced Raman tagging.

Glycomic analysis is an increasingly important field in biological and biomedical research as glycosylation is one of the most important protein post-translational modifications. We have developed a new technique to detect carbohydrates using surface enhanced Raman spectroscopy (SERS) by designing and applying a Rhodamine B derivative as the SERS tag. Using a reductive amination reaction, the Rhodamine-based tag (RT) was successfully conjugated to three model carbohydrates (glucose, lactose, and glucuronic acid).

Ultrasensitive detection of malondialdehyde with surface-enhanced Raman spectroscopy.

Malondialdehyde (MDA) is a biomarker of lipid peroxidation that has been widely associated with food rancidity as well as many human diseases. Most current MDA detection methods involve MDA reaction with thiobarbituric acid (TBA), followed by UV-visible and/or fluorescence detection of high-performance liquid chromatography (HPLC)-separated TBA-MDA. Herein, we report the first proof-of-concept study of surface-enhanced Raman detection of a TBA-MDA adduct using silver nanoparticles as the SERS substrate and the 632.

Inclusion complexes of buckycatcher with C(60) and C(70).

The dispersion corrected B97-D functional studies find a previously overlooked conformer of the buckycatcher C(60)H(28) (2) exhibiting intramolecular pi-pi stacking of its corannulene pincers to represent a global potential energy minimum conformation. B97-D/TZVP calculated geometry of C(60)@2 supramolecular assembly is in excellent agreement with the X-ray structure, slightly better than the previously reported M06-L results. In contrast, our calculated binding energy of C(60)@2 complex is dramatically higher than both M05-2X and M06-2X results and we conclude that the latter numbers are grossly underestimated.

Evidence for pi-stacking as a source of stereocontrol in the synthesis of the core pyranochromene ring system common to calyxin I, calyxin J, and epicalyxin J.

A diastereoselective synthesis of the tetrahydropyranochromene ring system common to several natural product isolates of Alpinia blepharocalyx is reported. We have shown that a stereochemical preference exists for a syn configuration between the anomeric aryl substituents, representative of the C-7 and C-7' substituents in the natural products. Further, our results show that stereocontrol is under kinetic control, and calculations suggest that a favorable pi-stacking interaction may be the source of this stereocontrol.

Ratiometric Raman spectroscopy for quantification of protein oxidative damage.

A novel ratiometric Raman spectroscopic (RMRS) method has been developed for quantitative determination of protein carbonyl levels. Oxidized bovine serum albumin (BSA) and oxidized lysozyme were used as model proteins to demonstrate this method. The technique involves conjugation of protein carbonyls with dinitrophenyl hydrazine (DNPH), followed by drop coating deposition Raman spectral acquisition (DCDR).

2-Trimethylsilylcorannulenyl trifluoromethanesulfonate: an efficient precursor for 1,2-didehydrocorannulene.

2-Trimethylsilylcorannulenyl trifluoromethanesulfonate, prepared from bromocorannulene, provides a means for generating of 1,2-didehydrocorannulene (corannulyne) under very mild conditions as demonstrated by the high-yield formation of its adducts with dienes.

Isocorannulenofuran: a versatile building block for the synthesis of large buckybowls.

Isocorannulenofuran, synthesized in two steps from accessible bromocorannulene, gives Diels-Alder adducts with benzynes which can be deoxygenated to produce large polycyclic aromatic hydrocarbons (PAHs) combining the bowl-shaped corannulene subunit with planar fragments. [reaction: see text]

The first buckybowl aryne. Corannulyne: a nonplanar benzyne.

[reaction: see text] Treatment of bromocorannulene with NaNH(2)/tBuOK in THF in the presence of furans or amines leads to formation of addition products in good yields, presumably through formation of 1,2-didehydrocorannulene (corannulyne). HDFT calculations predict that corannulyne exists as a bowl-shaped entity and that the didehydrogenation energy of corannulene is slightly lower than that of benzene.

Novel twin corannulene: synthesis and crystal structure determination of a dicorannulenobarrelene dicarboxylate.

[reaction: see text] The dicorannulenobarrelene 1 was synthesized with the final step achieved by a nickel-mediated fourfold intramolecular coupling of dibromomethyl with bromomethyl groups. Low-temperature (1)H NMR spectra of 1 show a presence of three conformers with approximate populations of 0.82:0.

Addition of organolithium reagents to corannulene and conformational preferences in 1-alkyl-1,2-dihydrocorannulenes.

Addition of organolithium reagents to corannulene (1) produces 1-R-1,2-dihydrocorannulenes (2), which can be easily converted to 1-R-corannulenes (3). Molecular mechanics (MM) calculations predict a slight pseudoequatorial preference for the small substituents in both exo and endo arrangements of 2, whereas bulky substituents are expected to favor strongly the exo-pseudoaxial location. X-ray diffraction studies show the exo-pseudoaxial conformation in the solid state for both i-Pr and t-Bu-2.

Formation of the corannulene core by nickel-mediated intramolecular coupling of benzyl and benzylidene bromides: a versatile synthesis of dimethyl 1,2-corannulene dicarboxylate.

[reaction: see text] A practical synthesis of dimethyl 1,2-corannulene dicarboxylate (5) is reported, with the final ring-forming step achieved by the double intramolecular nickel powder mediated coupling of benzyl and benzylidene bromide groups with 60% isolated yield.