Total Synthesis of the Schisandraceae Nortriterpenoid Rubriflordilactone A

Full details of the total synthesis of the Schisandraceae nortriterpenoid natural product rubriflordilactone A are reported. Palladium- and cobalt-catalyzed polycyclizations were employed as key strategies to construct the central pentasubstituted arene from bromoendiyne and triyne precursors. This required the independent assembly of two AB ring aldehydes for combination with a common diyne component. A number of model systems were explored to investigate these two methodologies, and also to establish routes for the installation of the challenging benzopyran and butenolide rings.

Total Synthesis of (+)-Rubriflordilactone A

Two enantioselective total syntheses of the nortriterpenoid natural product rubriflordilactone A are described, which use palladium- or cobalt-catalyzed cyclizations to form the CDE rings, and converge on a late-stage synthetic intermediate. These key processes are set up through the convergent coupling of a common diyne component with appropriate AB-ring aldehydes, a strategy that sets the stage for the synthetic exploration of other members of this family of natural products.

Carbopalladation of bromoene-alkynylsilanes: mechanistic insights and synthesis of fused-ring bicyclic silanes and phenols

Palladium-catalyzed cyclizations of silylated bromoenynes lead to bicyclic cyclohexadienes that are precursors to enones and phenols. Novel cyclization pathways and mechanistic insights are also disclosed.

Golden opportunities in catalysis

The gold-catalyzed endo-cycloisomerization of allenes bearing nucleophilic substituents in the α- or β-position opens up a versatile access to various five- and six-membered heterocycles. Key features of these transformations are the high reactivity of the allene in the presence of Lewis-acidic, carbophilic gold(I) or gold(III) catalysts, and the chirality transfer from the allenic axis of chirality to the new stereogenic center in the cyclization product. Recent contributions of our group include the optimization of chirality transfer by using σ-donor ligands to gold, and applications in the total synthesis of natural products, e.g., of the β-carboline alkaloids (-)-isocyclocapitelline and (-)-isochrysotricine.

Golden Times for Allenes: Gold-Catalyzed Cycloisomerization of β-Hydroxyallenes to Dihydropyrans

The gold(I)-catalyzed 6-endo cycloisomerization of beta-hydroxyallenes provides a mild and efficient access to chiral functionalized dihydropyrans which were obtained at room temperature in good chemical yields with axis-to-center chirality transfer. The method was extended to the beta-aminoallene 12, which afforded tetrahydropyridine 13 in good yield as well.

Transcoronary ablation of septal hypertrophy (TASH): a new treatment option for hypertrophic obstructive cardiomyopathy

In 1991, our group started to develop a catheter interventional therapy for hypertrophic obstructive cardiomyopathy (HOCM). The new concept was proposed in 1994. It is based on the conventional PTCA technique with the aim of inducing an artificial myocardial infarction by instillation of 96% ethanol into the most proximally situated septal branch of the left anterior descending coronary artery. This leads to a subaortic contraction disorder with subsequent decrease of the intraventricular pressure gradient, shrinkage of the hypertrophied septal bulge and widening of the outflow tract ("therapeutic remodeling"). The subaortic defect is small and well demarcated as assessed by left ventricular angiography, transesophageal echocardiography and 18 F-glucose positron emission tomography. The term transcoronary ablation of septum hypertrophy (TASH) was suggested. Our patient cohort that now comprises 215 therapeutic procedures in 187 patients underwent a large variety of prospective studies (maximum follow-up 4.5 years) including invasive controls at regular intervals, investigation of hemodynamics at rest and at exercise, transesophageal and transthoracic echocardiography, Doppler echocardiography during bicycle exercise, electrophysiologic testing, Holter monitoring and measurement of myocardial metabolism and perfusion, assessment of microembolic events by transcranial Doppler sonography and histological examinations. This article gives an overview and reports our increasing experience in applying TASH. The following post-TASH findings were obtained: significant hemodynamic and clinical improvement at rest and at exercise, decrease of septum thickness, increase of outflow tract area and decrease of induced ventricular tachycardia. There were well-demarcated, histologically atypical subaortic myocardial defects, no microembolic events, abnormal early peak of infarct related enzymes, and no change of baroreflex sensitivity. Pre-/post-TASH evaluations of the patients should be based in particular on clinical symptoms correlated to the intraventricular gradient measured by bicycle exercise Doppler echocardiography and to outflow tract area as assessed by transesophageal echocardiography. Since 1994, as a roughly estimate, worldwide 1000 patients in 20 countries have been treated. According to published articles, abstract presentations and workshops, TASH consistently leads to a pronounced clinical and hemodynamic benefit for patients with HOCM. TASH has become an established technique. At least in centers with a high level of expertise, it is no longer experimental but a routinely performed alternative to surgical treatment for HOCM, i.e., the previous gold standard of therapy. Of course, patient outcome needs further careful clinical and prognostic evaluation. With respect to complications, TASH appears to be superior to surgery (transaortic septal myectomy) for HOCM. Like surgical treatment, TASH is currently indicated in critically ill patients with typical HOCM (subaortic form), who exhibit with drug refractory symptoms, including patients, who preferred DDD pacemaker therapy as a first therapeutic step but in whom this produced no subsequent clinical benefit.

Changes in the left ventricular outflow tract after transcoronary ablation of septal hypertrophy (TASH) for hypertrophic obstructive cardiomyopathy as assessed by transoesophageal echocardiography and by measuring myocardial glucose utilization and perfusion

AIMS AND METHODS

Transcoronary ablation of septal hypertrophy (TASH) leads to marked clinical and haemodynamic improvement in patients with hypertrophic obstructive cardiomyopathy. In order to obtain more detailed information about changes in the outflow tract after TASH, transoesophageal echocardiography and a repeat invasive investigation were conducted before as well as 2 weeks and 6 months after TASH (n=62). In a subset of patients (n=11), metabolism and perfusion of the myocardium ((18)F-FDG-PET and(99m)Tc-MIBI-SPET) were investigated.

RESULTS

After TASH there was a typical regional subaortic contraction disorder. It was quantified by a significant decrease in the fractional shortening of the left ventricular end-diastolic diameter, which declined from an average of 40.6% to 18.0%. The end-diastolic diameter increased from an average of 39.1 to 40.6 mm. There was also a significant reduction in septal thickness, which continued for up to 6 months after TASH, from an average of 20.0 mm to 11.1 mm in the region of ablation and from 23. 2 to 21.7 mm outside this region. The decrease in the gradient post TASH corresponded with a concomitant significant increase in the outflow tract area from a mean value of 1.04 cm(2)before the process to a value of 3.0 cm(2)after. In contrast to coronary heart disease, these changes were accompanied by non-diffuse, well demarcated subaortic-septal necrosis verified by(18)F-FDG-PET and(99m)Tc-MIBI-SPET. On average the TASH induced necrotic area comprised 6.6% of the left ventricle and correlated significantly with echocardiographic changes in the outflow tract.

CONCLUSIONS

Alterations post TASH indicated that this catheter interventional treatment for hypertrophic obstructive cardiomyopathy affects the specific region of obstruction. The changes reflect a 'therapeutic remodelling' of the outflow tract of the left ventricle. They were demonstrable over the entire 6 months investigation period and obviously constituted the basis of post TASH clinical and haemodynamic improvement. Progressive alterations post TASH (post TASH reduction of subaortic septal thickness and an increase in the end-diastolic diameter) need special consideration during long-term follow up.

Gas exchange impairment and pulmonary densities after cardiac surgery

In 11 patients with impaired respiratory function after coronary artery revascularization surgery, thoracic computed tomography (TCT) and cardiopulmonary profile were obtained. The patients were haemodynamically stable without clinical or radiological signs of lung oedema. Oxygenation was reduced in all patients (alveolo-arterial PO2-difference (PA-aO2) = 37.3 +/- 10.39 kPa, venous admixture (QVA/QT) = 26.4 +/- 4.4%) during mechanical ventilation with positive end-expiratory pressure (PEEP = 5 cmH2O) (0.5 kPa). TCT-scan analysis revealed considerable amounts of crest-shaped bilateral densities in dependent lung regions. There were no differences between the right and left hemithorax. Atelectatic lung tissues were defined as areas presenting with attenuation values of -200 to +20 Hounsfield Units. The magnitude of non-ventilated areas correlated with QVA/QT (r = 0.875, P < or = 0.01), but not with the duration of either extracorporeal circulation, surgical procedure or general anaesthesia. It is concluded that atelectasis in dependent lung areas contributes to impaired gas exchange after cardiac surgery.