Ring-Closing Metathesis Approaches towards the Total Synthesis of Rhizoxins.

Efforts are described towards the total synthesis of the bacterial macrolide rhizoxin F, which is a potent tubulin assembly and cancer cell growth inhibitor. A significant amount of work was expanded on the construction of the rhizoxin core macrocycle by ring-closing olefin metathesis (RCM) between C(9) and C(10), either directly or by using relay substrates, but in no case was ring-closure achieved. Macrocycle formation was possible by ring-closing alkyne metathesis (RCAM) at the C(9)/C(10) site. The requisite diyne was obtained from advanced intermediates that had been prepared as part of the synthesis of the RCM substrates. While the direct conversion of the triple bond formed in the ring-closing step into the C(9)-C(10) E double bond of the rhizoxin macrocycle proved to be elusive, the corresponding Z isomer was accessible with high selectivity by reductive decomplexation of the biscobalt hexacarbonyl complex of the triple bond with ethylpiperidinium hypophosphite. Radical-induced double bond isomerization, full elaboration of the C(15) side chain, and directed epoxidation of the C(11)-C(12) double bond completed the total synthesis of rhizoxin F.

Mechanical Ventilation During Resuscitation: How Manual Chest Compressions Affect a Ventilator's Function.

INTRODUCTION: Guidelines for resuscitation recommend positive-pressure ventilation with a fixed ventilation rate as provided by an automated transport ventilator during cardiopulmonary resuscitation (CPR) with a secured airway. We investigated the influence of manual chest compressions (CC) on the accuracy of ventilator presets and the quality of CC with intermittent positive-pressure ventilation (IPPV), bilevel ventilation (BiLevel), and the novel ventilation mode chest compression synchronized ventilation (CCSV) in a simulation model. METHODS: Ninety paramedics performed continuous CC for 2 min on a modified advanced life support mannequin with a realistic lung model. IPPV, BiLevel, and CCSV were applied in a randomized order. CCSV is a novel type of pressure-controlled ventilation with short insufflations synchronized with CC, which are stopped before decompression begins. The ventilator presets (tolerance range) were IPPV Vt = 450 (400-500) ml, PEEP = 0 hPa, f = 10/min; BiLevel Pinsp = 19 (17.1-20.9) hPa, PEEP = 5 hPa, f = 10/min; CCSV Pinsp = 60 (54-66) hPa, PEEP = 0 hPa, Tinsp = 205 ms, f = CC rate. Preset values were compared with the measured results. Values were defined as correct within a tolerance range. Quality of CC was evaluated using ERC guidelines (depth >50 mm, CC rate 100-120/min). RESULTS: Median (25th/75th percentiles) IPPV V t = 399 (386/411) ml, BiLevel Pinsp = 22.0 (19.7/25.6) hPa, and CCSV Pinsp = 55.2 (52.6/56.7) hPa. Relative frequency of delivering correct ventilation parameters according to ventilation mode: IPPV = 40 (0/100)% vs. BiLevel = 20 (0/100)%, p = 0.37 and vs. CCSV = 71 (50/83)%, p < 0.02. Pinsp was too high in BiLevel = 80 (0/100)% vs. CCSV = 0(0/0)%, p < 0.001. CC depth: IPPV 56 (48/63) mm, BiLevel 57 (48/63) mm, CCSV 60 (52/67) mm; CC rate: IPPV 117 (105/124)/min, BiLevel 116 (107/123)/min, CCSV 117 (107/125)/min. CONCLUSION: When compared to IPPV and BiLevel, CCSV works best with preset values, without exceeding the upper pressure preset during simulated CPR. Quality of CC is not negatively affected by any of the ventilation patterns. FUNDING: Parts of this study were supported by Weinmann Emergency Medical Technology GmbH + Co.KG.

Chest Compression Synchronized Ventilation versus Intermitted Positive Pressure Ventilation during Cardiopulmonary Resuscitation in a Pig Model.

BACKGROUND: Guidelines recommend mechanical ventilation with Intermitted Positive Pressure Ventilation (IPPV) during resuscitation. The influence of the novel ventilator mode Chest Compression Synchronized Ventilation (CCSV) on gas exchange and arterial blood pressure compared with IPPV was investigated in a pig model. METHODS: In 12 pigs (general anaesthesia/intubation) ventricular fibrillation was induced and continuous chest compressions were started after 3 min. Pigs were mechanically ventilated in a cross-over setting with 5 ventilation periods of 4 min each: Ventilation modes were during the first and last period IPPV (100% O2, tidal volumes = 7 ml/kgKG, respiratory rate = 10/min), during the 2nd, 3rd and 4th period CCSV (100% O2), a pressure-controlled and with each chest compression synchronized breathing pattern with three different presets in randomized order. Presets: CCSVA: P insp = 60 mbar, inspiratory time = 205 ms; CCSVB: P insp = 60 mbar, inspiratory time = 265 ms; CCSVC: P insp = 45 mbar, inspiratory time = 265 ms. Blood gas samples were drawn for each period, mean arterial (MAP) and central venous (CVP) blood pressures were continuously recorded. Results as median (25%/75%percentiles). RESULTS: Ventilation with each CCSV mode resulted in higher PaO2 than IPPV: PaO2: IPPV first: 19.6(13.9/36.2)kPa, IPPV last: 22.7(5.4/36.9)kPa (p = 0.77 vs IPPV first), CCSVA: 48.9(29.0/58.2)kPa (p = 0.028 vs IPPV first, p = 0.0001 vs IPPV last), CCSVB: 54.0 (43.8/64.1) (p = 0.001 vs IPPV first, p = 0.0001 vs IPPV last), CCSVC: 46.0 (20.2/58.4) (p = 0.006 vs IPPV first, p = 0.0001 vs IPPV last). Both the MAP and the difference MAP-CVP did not decrease during twelve minutes CPR with all three presets of CCSV and were higher than the pressures of the last IPPV period. CONCLUSIONS: All patterns of CCSV lead to a higher PaO2 and avoid an arterial blood pressure drop during resuscitation compared to IPPV in this pig model of cardiac arrest.

A new tubulin-binding site and pharmacophore for microtubule-destabilizing anticancer drugs.

The recent success of antibody-drug conjugates (ADCs) in the treatment of cancer has led to a revived interest in microtubule-destabilizing agents. Here, we determined the high-resolution crystal structure of the complex between tubulin and maytansine, which is part of an ADC that is approved by the US Food and Drug Administration (FDA) for the treatment of advanced breast cancer. We found that the drug binds to a site on ß-tubulin that is distinct from the vinca domain and that blocks the formation of longitudinal tubulin interactions in microtubules. We also solved crystal structures of tubulin in complex with both a variant of rhizoxin and the phase 1 drug PM060184. Consistent with biochemical and mutagenesis data, we found that the two compounds bound to the same site as maytansine and that the structures revealed a common pharmacophore for the three ligands. Our results delineate a distinct molecular mechanism of action for the inhibition of microtubule assembly by clinically relevant agents. They further provide a structural basis for the rational design of potent microtubule-destabilizing agents, thus opening opportunities for the development of next-generation ADCs for the treatment of cancer.

Mechanical ventilation during cardiopulmonary resuscitation with intermittent positive-pressure ventilation, bilevel ventilation, or chest compression synchronized ventilation in a pig model.

OBJECTIVE: Mechanical ventilation with an automated ventilator is recommended during cardiopulmonary resuscitation with a secured airway. We investigated the influence of intermittent positive-pressure ventilation, bilevel ventilation, and the novel ventilator mode chest compression synchronized ventilation, a pressure-controlled ventilation triggered by each chest compression, on gas exchange, hemodynamics, and return of spontaneous circulation in a pig model. DESIGN: Animal study. SETTING: University laboratory. SUBJECTS: Twenty-four three-month-old female domestic pigs. INTERVENTIONS: The study was performed on pigs under general anesthesia with endotracheal intubation. Arterial and central venous catheters were inserted and IV rocuronium (1 mg/kg) was injected. After 3 minutes of cardiac arrest (ventricular fibrillation at t = 0 min), animals were randomized into intermittent positive-pressure ventilation (control group), bilevel, or chest compression synchronized ventilation group. Following 10 minute uninterrupted chest compressions and mechanical ventilation, advanced life support was performed (100% O2, up to six defibrillations, vasopressors). MEASUREMENTS AND MAIN RESULTS: Blood gas samples were drawn at 0, 4 and 13 minutes. At 13 minutes, hemodynamics was analyzed beat-to-beat in the end-inspiratory and end-expiratory cycle comparing the IPPV with the bilevel group and the CCSV group. Data were analyzed with the Mann-Whitney U test. Return of spontaneous circulation was achieved in five of eight (intermittent positive-pressure ventilation), six of eight (bilevel), and four of seven (chest compression synchronized ventilation) pigs. The results of arterial blood gas analyses at t = 4 minutes and t = 13 minutes (torr) were as follows: PaO2 intermittent positive-pressure ventilation, 143 (76/256) and 262 (81/340); bilevel, 261 (109/386) (p = 0.195 vs intermittent positive-pressure ventilation) and 236 (86/364) (p = 0.878 vs intermittent positive-pressure ventilation); and chest compression synchronized ventilation, 598 (471/650) (p < 0.001 vs intermittent positive-pressure ventilation) and 634 (115/693) (p = 0.054 vs intermittent positive-pressure ventilation); PaCO2 intermittent positive-pressure ventilation, 40 (38/43) and 45 (36/52); bilevel, 39 (35/41) (p = 0.574 vs intermittent positive-pressure ventilation) and 46 (42/49) (p = 0.798); and chest compression synchronized ventilation, 28 (27/32) (p = 0.001 vs intermittent positive-pressure ventilation) and 26 (18/29) (p = 0.004); mixed venous pH intermittent positive-pressure ventilation, 7.34 (7.31/7.35) and 7.26 (7.25/7.31); bilevel, 7.35 (7.29/7.37) (p = 0.645 vs intermittent positive-pressure ventilation) and 7.27 (7.17/7.31) (p = 0.645 vs intermittent positive-pressure ventilation); and chest compression synchronized ventilation, 7.34 (7.33/7.39) (p = 0.189 vs intermittent positive-pressure ventilation) and 7.35 (7.34/7.36) (p = 0.006 vs intermittent positive-pressure ventilation). Mean end-inspiratory and end-expiratory arterial pressures at t = 13 minutes (mm Hg) were as follows: intermittent positive-pressure ventilation, 28.0 (25.0/29.6) and 27.9 (24.4/30.0); bilevel, 29.1 (25.6/37.1) (p = 0.574 vs intermittent positive-pressure ventilation) and 28.7 (24.2/36.5) (p = 0.721 vs intermittent positive-pressure ventilation); and chest compression synchronized ventilation, 32.7 (30.4/33.4) (p = 0.021 vs intermittent positive-pressure ventilation) and 27.0 (24.5/27.7) (p = 0.779 vs intermittent positive-pressure ventilation). CONCLUSIONS: Both intermittent positive-pressure ventilation and bilevel provided similar oxygenation and ventilation during cardiopulmonary resuscitation. Chest compression synchronized ventilation elicited the highest mean arterial pressure, best oxygenation, and a normal mixed venous pH during cardiopulmonary resuscitation.

Kinase inhibition by deoxy analogues of the resorcylic lactone L-783277.

The natural product L-783277 is a resorcylic lactone type covalent kinase inhibitor. We have prepared the 5'-deoxy analogue of L-783277 (1) in a stereoselective fashion. Remarkably, this analogue retains almost the full kinase inhibitory potential of natural L-783277, with low nanomolar IC50 values against the most sensitive kinases, and it exhibits essentially the same selectivity profile (within the panel of 39 kinases investigated). In contrast, removal of both the 4'- and the 5'-hydroxyl groups leads to a more significant reduction in kinase inhibitory activity and so does a change in the geometry of the C7'-C8' double bond in 1 from Z to E. These findings offer new perspectives for the design of second generation resorcylic lactone-based kinase inhibitors.