From Serendipity to Rational Design: Heteroleptic Dirhodium Amidate Complexes for Diastereodivergent Asymmetric Cyclopropanation.

A heteroleptic dirhodium paddlewheel complex comprising three chiral carboxylate ligands and one achiral acetamidate ligand has recently been found to be uniquely effective in catalyzing the asymmetric cyclopropanation of olefins with α-stannylated (silylated and germylated) α-diazoacetate derivatives. A number of control experiments in combination with detailed computational studies provide compelling evidence that an interligand hydrogen bond between the -NH group of the amidate and the ester carbonyl group of the reactive rhodium carbene intermediate plays a quintessential role in the stereodetermining transition state. The penalty for distorting this array outweighs steric arguments and renders two of the four conceivable transitions states unviable. Based on this mechanistic insight, the design of the parent catalyst is revisited herein: placement of appropriate peripheral substituents allows high levels of diastereocontrol to be imposed upon cyclopropanation, which the original catalyst lacks. Because the new complexes allow either trans- or cis-configured stannylated cyclopropanes to be made selectively and in excellent optical purity, this transformation also marks a rare case of diastereodivergent asymmetric catalysis. The products are amenable to stereospecific cross coupling with aryl halides or alkenyl triflates; these transformations appear to be the first examples of the formation of stereogenic quaternary carbon centers by the Stille reaction; carbonylative coupling is also achieved. Moreover, tin/lithium exchange affords chiral lithium enolates, which can be intercepted with a variety of electrophilic partners. The virtues and inherent flexibility of this new methodology are illustrated by an efficient synthesis of two salinilactones, extremely scarce bacterial metabolites with signaling function involved in the self-regulatory growth inhibition of the producing strain.

Awakening a Molecular Mummy: The Inter-and Intramolecular Photochemistry of Pyromellitic Diimides with Alkyl Carboxylates.

Pyromellitic acid diimides are not as chemically unreactive as conjecturable (and presupposed) from their numerous applications as electron acceptor units or electron carriers in molecular donor-acceptor dyads or triads. Similar to the corresponding phthalimides, electronically excited pyromellitic diimides oxidize alkyl carboxylates in aqueous solution via intermolecular electron transfer (PET) processes, which eventually results in radical-radical combination products, e.g., the benzylation product 6 from N,N'-dimethyl pyromellitic diimide 5. The analogous product 7 was formed with pivalic acid as tert-butyl radical source. One additional product 8 was isolated from alkylation/dearomatization and multiple radical additions, respectively, after prolonged irradiation. In intramolecular versions, from N-carboxyalkylated pyromellitic diimides 9a-e (C1 to C5-spaced), degradation processes were detected, e.g., the cyclization products 10 from the GABA substrate 9c. In sharp contrast to phthalimide photochemistry, the green pyromellitic diimide radical anion was detected here by UV-vis absorption (λabs = 720 nm), EPR (from 9d), and NMR spectroscopy for several intramolecular electron transfer examples. Only the yellow 1,4-quinodial structure is formed from intermolecular PET, which was deduced from the absorption spectra (λabs = 440 nm) and the subsequent chemistry. The pyromellitimide radical anion lives for hours at room temperature in the dark, but is further degraded under photochemical reaction conditions.

Total Synthesis of α-Tocopherol through Enantioselective Iridium-Catalyzed Fragmentation of a Spiro-Cyclobutanol Intermediate.

A conceptionally new strategy for the asymmetric (2R-selective) synthesis of α-tocopherol (vitamin E) was developed. In the stereocontrolled key step, a prochiral spiro[chromane-2,3'-cyclobutanol] unit is effectively desymmetrized under C-C bond activation in an unprecedented iridium-catalyzed transformation using (S)-DTBM-SegPhos as a chiral ligand (e.r. 97:3). To complete the synthesis, the side chain was attached through Ru-catalyzed cross-metathesis employing an alkene derived from (R,R)-hexahydrofarnesol. To suppress epimerization during the final hydrogenation, PtO2 had to be used as a catalyst instead of Pd/C. In an alternative approach (employing a propargyl-substituted spiro-cyclobutanol), the side chain was constructed prior to the Ir-catalyzed ring fragmentation (>99:1 d.r.) through enyne cross-metathesis (using an alkene derived from (R)-dihydrocitronellal) followed by Cr-catalyzed 1,4-hydrogenation and (diastereoselective) Pfaltz hydrogenation of the resulting triple-substituted olefin. The work demonstrates the potential of iridium catalysis for enantioselective C-C bond activation.

Endocannabinoids limit excessive mast cell maturation and activation in human skin.

BACKGROUND: Mast cells (MCs) crucially contribute to many inflammatory diseases. However, the physiological controls preventing excessive activities of MCs in human skin are incompletely understood. OBJECTIVE: Since endocannabinoids are important neuroendocrine MC modifiers, we investigated how stimulation/inhibition of cannabinoid 1 (CB1) receptors affect the biology of human skin MCs in situ. METHODS: This was investigated in the MC-rich connective tissue sheath of organ-cultured human scalp hair follicles by quantitative (immuno)histomorphometry, ultrastructural, and quantitative PCR techniques with the use of CB1 agonists or antagonists, CB1 knockdown, or CB1 knockout mice. RESULTS: Kit+ MCs within the connective tissue sheath of human hair follicles express functional CB1 receptors, whose pharmacological blockade or gene silencing significantly stimulated both the degranulation and the maturation of MCs from resident progenitor cells in situ (ie, enhanced the number of tryptase+, FcεRIα, or chymase+ connective tissue sheath-MCs). This was, at least in part, stem cell factor-dependent. CB1 agonists counteracted the MC-activating effects of classical MC secretagogues. Similar phenomena were observed in CB1 knockout mice, attesting to the in vivo relevance of this novel MC-inhibitory mechanism. CONCLUSION: By using human hair follicle organ culture as an unconventional, but clinically relevant model system for studying the biology of MCs in situ, we show that normal skin MCs are tightly controlled by the endocannabinoid system. This limits excessive activation and maturation of MCs from resident progenitors via "tonic" CB1 stimulation by locally synthesized endocannabinoids. The excessive numbers and activation of MCs in allergic and other chronic inflammatory skin diseases may partially arise from resident intracutaneous MC progenitors, for example, because of insufficient CB1 stimulation. Therefore, CB1 stimulation is a promising strategy for the future management of allergy and MC-dependent skin diseases.

Deficits in sensory-specific devaluation task performance following genetic deletions of cannabinoid (CB1) receptor.

Cannabinoid CB1 receptor is abundantly expressed throughout the CNS and is implicated in numerous physiological and behavioral functions, including appetite and feeding. In the present study, wild-type and CB1 heterozygous and homozygous knockout mice were tested on an instrumental outcome-selective devaluation task to assess changes in acquired instrumental response levels for a distinct food reward following selective satiation. Deletion of CB1 receptor, as well as reduction in CB1 expression (HET), produced deficits in outcome-selective instrumental devaluation. These results identify a critical role for CB1 receptor in the ability of animals to represent, update, and/or use sensory-specific outcome representations to alter appetitive behaviors.

Control of hormonal stress reactivity by the endogenous opioid system.

Regulations of hormonal stress responses entail the initiation, amplitude and termination of the reaction, as well as its integration with other stress response systems. This study investigates the role of endogenous opioids in the regulation and integration of behavioral, thermal and hormonal stress responses, as these neuromodulators and their receptors are expressed in limbic structures responsible for stress responses. For this purpose, we subjected mice with selective deletion of beta-endorphin, enkephalin or dynorphin to the zero-maze test, a mildly stressful situation, and registered behaviors and stress hormone levels. Behavioral stress reactivity was assessed using zero-maze, light-dark and startle-reactivity paradigms. Animals lacking enkephalin displayed increased anxiety-related behavioral responses in each three, dynorphin knockouts in two models, whereas the responses of beta-endorphin knockouts indicated lower anxiety level in the zero-maze test. All knockout strains showed marked changes in hormonal stress reactivity. Increase in ACTH level after zero-maze test situation, unlike in wild type animals, failed to reach the level of significance in Penk1(-/-) and Pdyn(-/-) mice. Corticosterone plasma levels rapidly increased in all strains, with a lower peak response in knockouts. In wild-type and beta-endorphin-deficient mice, corticosterone levels returned to baseline within 60min after stress exposure. In contrast, mice lacking dynorphin and enkephalin showed longer-lasting elevated corticosterone levels, indicating a delayed termination of the stress reaction. Importantly, the behavioral and hormonal responses correlated in wild-type but not in knockout mice. Hyperthermia elicited by stress was reduced in animals lacking dynorphin and absent in Penk1(-/-) mice, despite of the heightened behavioral anxiety level of these strains. These results demonstrate an important role on the endogenous opioid system in the integration of behavioral and hormonal stress responses.

A tarantula peptide against pain via ASIC1a channels and opioid mechanisms.

Psalmotoxin 1, a peptide extracted from the South American tarantula Psalmopoeus cambridgei, has very potent analgesic properties against thermal, mechanical, chemical, inflammatory and neuropathic pain in rodents. It exerts its action by blocking acid-sensing ion channel 1a, and this blockade results in an activation of the endogenous enkephalin pathway. The analgesic properties of the peptide are suppressed by antagonists of the mu and delta-opioid receptors and are lost in Penk1-/- mice.

The influence of ascending aortic atherosclerosis on the long-term survival after CABG.

OBJECTIVE: Ascending aortic atherosclerosis is a risk factor for perioperative morbidity and mortality in coronary surgery. It was the aim of our study to determine the role of atherosclerosis of the ascending aorta and other factors for the survival rate during long-term follow-up after CABG. METHODS: From 500 out of 580 CABG patients (aged 67 (33-85) years, 77% male), who underwent intraoperative epiaortic ultrasound for assessment of ascending aortic wall thickness, a complete follow up regarding long-term survival was achieved. The median follow-up time was 55 (1-78) months. RESULTS: 53/500 (11%) patients died within the follow-up period, and the cumulative survival rate was 95, 90, and 84% after 1, 3, and 5 years, respectively (including hospital deaths). A significantly lower long-term survival was present in patients with: an age of 70 years or more (P<0.001), COPD (P=0.005), preoperative elevated serum creatinine of >1.2mg/dl (P=0.007), preoperative LVEF <40% (P=0.033), ascending aortic wall thickness of 4mm or more (P=0.001), carotid artery disease (P<0.001), peripheral vascular disease (P<0.001), and acute operation (P=0.009). Multivariate analysis revealed carotid artery disease, LVEF <40%, peripheral vascular disease, and advanced age to be independent risk factors. CONCLUSION: Patients with ascending aortic atherosclerosis are at risk for a decreased long-term survival after CABG. Besides, preoperative elevated serum creatinine, COPD, carotid artery disease, LVEF <40%, peripheral vascular disease, and advanced age are risk factors for a decreased long-term survival after CABG.

Risk factors for late stroke after coronary artery bypass grafting.

BACKGROUND: Postoperative stroke is a severe complication immediately after coronary artery bypass grafting, and it significantly deteriorates the postoperative quality of life if it occurs in the long term. It was the aim of our study to determine factors associated with the occurrence of new strokes during long-term follow-up after coronary artery bypass grafting. METHODS: From 387 of 500 patients undergoing coronary artery bypass grafting (age, 67 years [33-84 years]; 76% male) who had intraoperative epiaortic ultrasonography for assessment of ascending aortic wall thickness, a complete follow-up regarding postoperative stroke was achieved. The median follow-up time was 52 months (9-74 months). RESULTS: A stroke occurred in 26 (7%) of 387 patients, and the cumulative freedom from stroke was 99%, 95%, and 89% after 1, 3, and 5 years, respectively. A significantly lower freedom from stroke was present in patients with an age of 70 years or more (P = .007), preoperative unstable angina (P = .031), chronic obstructive pulmonary disease (P = .009), carotid artery disease (P < .001), preoperative history of neurologic events (P < .001), and a maximum ascending aortic wall thickness of 4 mm or more (P = .010). Multivariate analysis revealed preoperative history of neurologic events (P = .021) to be an independent risk factor. CONCLUSION: Patients with ascending aortic atherosclerosis, older age (> or =70 years), preoperative unstable angina, chronic obstructive pulmonary disease, and carotid artery disease are at risk for late postoperative stroke after coronary artery bypass grafting. A history of neurologic events is of special predictive importance.

Technical problems and complications of axillary artery cannulation.

OBJECTIVE: Cardiopulmonary bypass via the axillary artery is frequently used especially in aortic dissections. With an increased use of this technique problems were recognized too. We describe the technical problems and complications associated with axillary artery cannulation. METHODS: Sixty-five patients underwent cannulation of the axillary artery. The indication for operation was acute aortic dissection type A in 57%, chronic aortic dissection in 8%, aortic aneurysm in 18%, pseudoaneurysm in 3%, and others in 14%. RESULTS: Technical problems and complications occurred in 14%, and in 11% the perfusion had to be switched to either femoral (n=5) or aortic cannulation (n=2). Arterial damage or dissection of the axillary artery or the aorta occurred in 0% of the sidegraft technique, whereas they were found in 9% with direct cannulation (P=n.s.). Cannulation problems or insufficient CPB flow due to a narrow vessel occurred in 0% of the sidegraft technique, whereas they were found in 4% with direct cannulation (P=n.s.). Malperfusion in aortic dissections occurred in 20% of the sidegraft technique, whereas they were found in 0% with direct cannulation (P=0.016). No postoperative complications related to axillary cannulation which were evaluated by clinical examination, such as brachial plexus injury, axillary artery thrombosis or local wound infection were observed. CONCLUSIONS: Although axillary artery cannulation is an attractive alternative to femoral cannulation there needs to be an alertness for technical problems. Different complications occur with either direct cannulation or the sidegraft technique and at present it remains the surgeons preference which technique for axillary artery cannulation is used.

Behavioral phenotype of pre-proenkephalin-deficient mice on diverse congenic backgrounds.

RATIONALE: The phenotype of genetically modified animals is thought to result from an interaction of gene manipulation with the genetic background and environmental factors. OBJECTIVES: To test the behavioral and drug responses of Penk1(-/-) mice on different genetic backgrounds. METHODS: Congenic C57BL/6J and DBA/2J mouse strains with a targeted deletion of the Penk1 gene were generated. Behavior and drug effects were tested in models of pain and anxiety. RESULTS: Penk1(-/-) mice showed exaggerated responses to painful or threatening environmental stimuli, but the expressivity of the mutant phenotype was strongly dependent on the behavioral paradigm and on the genetic background. For example, elevated levels of anxiety were readily detectable in C57BL/6J-Penk1(-/-) mice in the light-dark and startle response tests, but not in the social interaction test. In contrast, we found elevated levels of anxiety in DBA/2J-Penk1(-/-) mice only in the zero-maze and social interaction tests. In some cases, the idiosyncratic behavior masked the appearance of the knockout gene effect. The activity of the anxiogenic drug, m-chlorophenylpiperazine, but not the anxiolytic drug diazepam, was strain and genotype dependent. Mice with the Penk1 mutation on the DBA/2J, but not on other genetic backgrounds, showed an increased opioid-dependent stress-induced analgesia. CONCLUSIONS: (1) The behavioral effects of the Penk1 gene deletion persists on different genetic backgrounds, but its detection sometimes requires the use of different behavioral paradigms. (2) The behavior of the background strain should be considered in the analysis of knockout mice to avoid floor and ceiling effects, which may mask the phenotype.

A role for ASIC3 in the modulation of high-intensity pain stimuli.

Acid-sensing ion channel 3 (ASIC3), a proton-gated ion channel of the degenerins/epithelial sodium channel (DEG/ENaC) receptor family is expressed predominantly in sensory neurons including nociceptive neurons responding to protons. To study the role of ASIC3 in pain signaling, we generated ASIC3 knockout mice. Mutant animals were healthy and responded normally to most sensory stimuli. However, in behavioral assays for pain responses, ASIC3 null mutant mice displayed a reduced latency to the onset of pain responses, or more pain-related behaviors, when stimuli of moderate to high intensity were used. This unexpected effect seemed independent of the modality of the stimulus and was observed in the acetic acid-induced writhing test (0.6 vs. 0.1-0.5%), in the hot-plate test (52.5 and 55 vs. 50 degrees C), and in tests for mechanically induced pain (tail-pinch vs. von Frey filaments). We postulate that ASIC3 is involved in modulating moderate- to high-intensity pain sensation.