Selective and Sequential Aminolysis of Benzotrifuranone: Synergism of Electronic Effects and Ring Strain Gradient.

Benzotrifuranone (BTF), bearing three symmetry-equivalent lactone rings, is unique in its ability to undergo highly selective and sequential aminolysis reactions in one-pot to afford multifunctionalized molecules (>80% overall yield). New insight into this behavior is presented through kinetics measurements (by stopped-flow IR spectroscopy), X-ray crystal structure analysis, quantum chemical calculations, and comparison of BTF to other benzoate esters, including its ring expanded congener benzotripyranone (BTP). While the structure-property investigation confirms stepwise electronic/inductive lactone deactivation for both BTF and BTP, the unusually fast and selective aminolysis of BTF is only fully explained through synergistic ring strain effects. Experimental signatures of the significant ring strain of BTF (∼28 kcal mol-1 based on DFT calculations vs 17 kcal mol-1 for BTP) include its high lactone carbonyl stretching energy (1821 cm-1 in acetonitrile vs 1777 cm-1 for BTP) and bond length alternation within its benzenoid ring. While ring strain is relieved upon the sequential aminolysis of both BTF and BTP, it is only for the former that a ring strain gradient is established that contributes to the stepwise aminolysis rate differences and enhanced selectivity. The work shows how a combination of electronic effects and ring strain can underpin the design of small molecules capable of stepwise functionalization, of which there are notably few examples.

Evaluation of fluorescent phosphatidylserine substrates for the aminophospholipid flippase in mammalian cells.

A series of fluorescent phosphatidylserine and phosphatidylcholine derivatives were prepared and evaluated by cell microscopy for ability to translocate across mammalian plasma membranes via the putative aminophospholipid flippase. Phosphatidylserine derivatives, with either a neutral 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD) or a coumarin fluorophore appended to the 2-acyl chain, entered the cytosol of all three cell lines tested and control experiments showed that the translocation was due to flippase activity. In contrast, a phosphatidylserine conjugate containing a charged and polar carboxyfluorescein was not translocated and remained in the cell plasma membrane. The phosphatidylserine-coumarin derivative exhibits bright fluorescence and higher photostability than the NBD analogues, and thus is a promising new fluorescent probe for extended-imaging studies of flippase action in living cells using laser confocal microscopes.

Optical imaging of mammary and prostate tumors in living animals using a synthetic near infrared zinc(II)-dipicolylamine probe for anionic cell surfaces.

In vivo optical imaging shows that a fluorescent imaging probe, comprised of a near-infrared fluorophore attached to an affinity group containing two zinc(II)-dipicolylamine (Zn-DPA) units, targets prostate and mammary tumors in two different xenograft animal models. The tumor selectivity is absent with control fluorophores whose structures do not have appended Zn-DPA targeting ligands. Ex vivo biodistribution and histological analyses indicate that the probe is targeting the necrotic regions of the tumors, which is consistent with in vitro microscopy showing selective targeting of the anionic membrane surfaces of dead and dying cells.

Bio-orthogonal phosphatidylserine conjugates for delivery and imaging applications.

The syntheses of phosphatidylserine (PS) conjugates are described, including fluorescent derivatives for potential cellular delivery and bioimaging applications. Installation of terminal functional groups (amine, thiol, or alkyne) onto the sn-2 chain provides reactive sites for bio-orthogonal conjugation of cargo with suitably protected PS derivatives. An amine-containing PS forms amide bonds with peptidic cargo, a thiol derivative is designed for conjugation to cargo that contain alpha-halo carbonyls or Michael acceptors, and the terminal alkyne PS analogue permits "click" conjugation with any azide-tagged molecule. This latter conjugation method is quite versatile as it can be performed without PS headgroup protection, in aqueous media, and with acid-labile cargo.

Enhanced small-molecule assembly through directional intramolecular forces.

[reaction: see text] Directional intramolecular interactions play a critical role in the self-assembly of donor-sigma-acceptor molecules in solution. Amide functions on the periphery of the tricyclic core stabilize a C3-symmetric monomer conformation by intramolecular hydrogen bonding and dipole-dipole interactions. The molecules are effective organogelators and show long-range ordering in the bulk.

Synthesis and self-assembly of functionalized donor-sigma-acceptor molecules.

[structure: see text] 3,5,7-Tris(arylmethyl)-1-aza-adamantanetrione donor-sigma-acceptor compounds have been synthesized in four steps. Computational and (1)H NMR analyses rationalize the solubility, gelation, and conformational properties of the C3-symmetric molecules toward employing sigma-coupled donor-acceptor interactions in molecular self-assembly.

Benzotrifuranone: synthesis, structure, and access to polycyclic heteroaromatics.

Functionalized benzotrifurans can be accessed in one efficient acylation step from previously unreported benzotrifuranone. DFT calculations have confirmed the aromaticity of the heteroaromatic system and determined its electronic structure that is relevant to applications in materials and supramolecular chemistry.

Assessable consequences of through-bond donor-acceptor interactions in beta-aminoketones.

Reported are the syntheses of ester-functionalized (6-8) and alkyl-substituted (9) 1-aza-adamantanones; the easy handling of the compounds provides an opportunity to comprehensively study the fundamental changes in structure and reactivity that can accompany the donor-acceptor arrangement in rigid beta-aminoketones. X-ray structural analysis of trione 6 and dione 7 reveals bond length and angle variations consistent with through-bond (hyperconjugative) donor-acceptor interactions. Observed is a shortening of the C-N bond, elongation of the central C-C bond (to approximately 1.6 A), and a significant pyramidalization of the carbonyl carbon within the donor-sigma-acceptor pathway. UV/Vis spectra of 6-9 show a new absorption maximum (lambda(max)=260-275 nm in three solvents), the so-called "sigma-coupled transition"; the molar absorptivity scales with the number of carbonyl groups (for trione 6, epsilon approximately 3000, for dione 7, epsilon approximately 2000) and the band reversibly disappears upon addition of acid. IR and (13)C NMR spectroscopic data show trends consistent with through-bond donation to the carbonyl acceptor groups and commensurate weakening of the carbonyl pi bond. High yielding acid-mediated fragmentations are used to illustrate the effects of the donor-acceptor arrangement on the reactivity of the molecules. Given that donor-sigma-acceptor molecules have recently been found to show self-assembly behavior and macromolecular properties linked to their unusual structure, the current analysis encourages further consideration of the systems in advanced materials applications.

Structure-based identification of small-molecule angiotensin-converting enzyme 2 activators as novel antihypertensive agents.

Angiotensin-converting enzyme 2 (ACE2) is a key renin-angiotensin system enzyme involved in balancing the adverse effects of angiotensin II on the cardiovascular system, and its overexpression by gene transfer is beneficial in cardiovascular disease. Therefore, our objectives were 2-fold: to identify compounds that enhance ACE2 activity using a novel conformation-based rational drug discovery strategy and to evaluate whether such compounds reverse hypertension-induced pathophysiologies. We used a unique virtual screening approach. In vitro assays revealed 2 compounds (a xanthenone and resorcinolnaphthalein) that enhanced ACE2 activity in a dose-dependent manner. Acute in vivo administration of the xanthenone resulted in a dose-dependent transient and robust decrease in blood pressure (at 10 mg/kg, spontaneously hypertensive rats decreased 71+/-9 mm Hg and Wistar-Kyoto rats decreased 21+/-8 mm Hg; P<0.05). Chronic infusion of the xanthenone (120 microg/day) resulted in a modest decrease in the spontaneously hypertensive rat blood pressure (17 mm Hg; 2-way ANOVA; P<0.05), whereas it had no effect in Wistar-Kyoto rats. Strikingly, the decrease in blood pressure was also associated with improvements in cardiac function and reversal of myocardial, perivascular, and renal fibrosis in the spontaneously hypertensive rats. We conclude that structure-based screening can help identify compounds that activate ACE2, decrease blood pressure, and reverse tissue remodeling. Administration of ACE2 activators may be a valid strategy for antihypertensive therapy.

Noninvasive optical imaging of staphylococcus aureus bacterial infection in living mice using a Bis-dipicolylamine-Zinc(II) affinity group conjugated to a near-infrared fluorophore.

Optical imaging of bacterial infection in living animals is usually conducted with genetic reporters such as light-emitting enzymes or fluorescent proteins. However, there are many circumstances where genetic reporters are not applicable, and there is a need for exogenous synthetic probes that can selectively target bacteria. The focus of this study is a fluorescent imaging probe that is composed of a bacterial affinity group conjugated to a near-infrared dye. The affinity group is a synthetic zinc (II) coordination complex that targets the anionic surfaces of bacterial cells. The probe allows detection of Staphylococcus aureus infection (5 x 10 (7) cells) in a mouse leg infection model using whole animal near-infrared fluorescence imaging. Region of interest analysis showed that the signal ratio for infected leg to uninfected leg reaches 3.9 +/- 0.5 at 21 h postinjection of the probe. Ex vivo imaging of the organs produced a signal ratio of 8 for infected to uninfected leg. Immunohistochemical analysis confirmed that the probe targeted the bacterial cells in the infected tissue. Optimization of the imaging filter set lowered the background signal due to autofluorescence and substantially improved imaging contrast. The study shows that near-infrared molecular probes are amenable to noninvasive optical imaging of localized S. aureus infection.

Remote asymmetric induction about a crowded aromatic core.

Described are among the first highly diastereoselective, one-pot organometallic addition and hydride reduction reactions (>95% de) involving three symmetry-equivalent carbonyl centers, each that bears a 1,5-relationship to its nearest neighbor. Three-fold methyllithium addition to 2,4,6-trimethoxybenzene-1,3,5-tricarbaldehyde gives the anti,syn triol exclusively (by 1H NMR); addition of HMPA to the reaction or replacement of the substrate's methoxy groups with ethyl groups affords a statistical 3:1 (anti,syn:syn,syn) diastereomeric product ratio. Analogous asymmetric induction is found upon hydride reduction (using LiAlH4 or NaBH4) of the complementary triketone, 2,4,6-trimethoxybenzene-1,3,5-triethanone. Chelation and steric (gearing) effects about the crowded aromatic core contribute to the observed stereoselectivity.