Synthesis of Waixenicin A: Exploring Strategies for Nine-Membered Ring Formation

We present a comprehensive account on our efforts behind the recently published synthesis of waixenicin A. Our approach for constructing the dihydropyran ring relied on an Achmatowicz rearrangement. For the assembly of the nine-membered ring, four distinct strategies were investigated. Our initial attempts using radical-based addition/fragmentation reactions targeting the C7-C11 bond proved unsuitable for accessing the 6/9-bicycle. By employing anionic fragmentation conditions at the furfuryl alcohol stage, we successfully reached a 5/9-bicycle. However, subsequent ring-expansion was unsuccessful. Alternative approaches, such as Nozaki-Hiyama-Kishi or Heck reactions to connect the C6-C7 bond, also encountered difficulties, with no nine-membered ring formation observed. Our first breakthrough came from our attempts to install the C5-C6 bond via an intramolecular alkylation. Surprisingly, subsequent functional group modifications proved unexpectedly challenging, necessitating a redesign of our synthetic route. Drawing from all our investigations, we concluded that construction of the C9-C10 bond would enable efficient nine-membered ring alkylation and would facilitate the installation of the desired substitution pattern along the southern periphery. Exploration of this strategy yielded further surprises but ultimately led to the successful synthesis of waixenicin A and 9-deacetoxy-14,15-deepoxyxeniculin. For the latter compound, a bioinspired one-step rearrangement to xeniafauranol A was achieved.

Investigations into Simplified Analogues of the Herbicidal Natural Product (+)-Cornexistin

We report the design, synthesis and biological evaluation of simplified analogues of the herbicidal natural product (+)-cornexistin. Guided by an X-Ray co-crystal structure of cornexistin bound to transketolase from Zea mays, we attempted to identify the key interactions that are necessary for cornexistin to maintain its herbicidal profile. This resulted in the preparation of three novel analogues investigating the importance of substituents that are located on the nine-membered ring of cornexistin. One analogue maintained a good level of biological activity and could provide researchers insights in how to further optimize the structure of cornexistin for commercialization in the future.

Total Syntheses of (+)-Waixenicin A, (+)-9-Deacetoxy-14,15-deepoxyxeniculin, and (-)-Xeniafaraunol A

The first asymmetric total synthesis of the Xenia diterpenoid waixenicin A, a potent and highly selective TRPM7 inhibitor, is reported. The characteristic trans-fused oxabicyclo[7.4.0]tridecane ring system was constructed via a diastereoselective conjugate addition/trapping sequence, followed by an intramolecular alkylation to forge the 9-membered ring. While a β-keto sulfone motif enabled efficient ring-closure, the subsequent radical desulfonylation suffered from (E)/(Z)-isomerization of the C7/C8-alkene. Conducting the sequence with a trimethylsilylethyl ester allowed for a fluoride-mediated decarboxylation that proceeded without detectable isomerization. The acid-labile enol acetal of the delicate dihydropyran core was introduced at an early stage and temporarily deactivated by a triflate function. The latter was critical for the introduction of the side chain. Diverting from a common late-stage intermediate provided access to waixenicin A and 9-deacetoxy-14,15-deepoxyxeniculin. A high-yielding base-mediated dihydropyran-cyclohexene rearrangement of 9-deacetoxy-14,15-deepoxyxeniculin led to xeniafaraunol A in one step.

Evolution of a Strategy for the Total Synthesis of (+)-Cornexistin

Herein is given a full account of the evolution of the first total synthesis of (+)-cornexistin. Initial efforts were based on masking the reactive maleic anhydride moiety as a 3,4-substituted furan and on forming the nine-membered carbocycle in an intramolecular Conia-ene or Nozaki-Hiyama-Kishi (NHK) reaction. Those strategies suffered from low yields and were jeopardized by a late-stage installation of the Z-alkene, as well as the stereocenters along the eastern periphery. These issues were addressed by employing a chiral-pool strategy that involved construction of the crucial stereocenters at C2, C3 and C8 at an early stage with installation of the maleic anhydride as late as possible. The successful approach featured an intermolecular NHK coupling to install the Z-alkene, a syn-Evans-aldol reaction to forge the stereocenters along the eastern periphery, an intramolecular allylic alkylation to close the nine-membered carbocycle, and a challenging stepwise hydrolysis of a β-keto nitrile to furnish the maleic anhydride.

Total Synthesis of (+)-Cornexistin

Herein, we describe the first total synthesis of (+)-cornexistin as well as its 8-epi-isomer starting from malic acid. The robust and scalable route features a Nozaki-Hiyama-Kishi reaction, an auxiliary-controlled syn-Evans-aldol reaction, and a highly efficient intramolecular alkylation to form the nine-membered carbocycle. The delicate maleic anhydride moiety of the nonadride skeleton was constructed from a β-keto nitrile. The developed route enabled the synthesis of 165 mg (+)-cornexistin.

Effects of the 5-HT3 antagonist cilansetron vs placebo on phasic sigmoid colonic motility in healthy man: a double-blind crossover trial

AIMS

5-hydroxytryptamine3 receptor antagonists act antiemetically and slow colonic transit. This study evaluated effects of the high-affinity 5-HT3 antagonist, cilansetron, on fasting, meal-and anticholinesterase-stimulated phasic contractile activity of the human sigmoid colon as well as on bowel habits and stool consistency.

METHODS

Five female and seven male healthy volunteers received, during three 7 day periods separated by 7 day wash-out periods, 4 mg cilansetron, 8 mg cilansetron or placebo three times daily orally under random, double-blind, crossover conditions. On day 8 of each treatment period, motility 20-40 cm from the anal verge was recorded using five pressure sensors spaced at 5 cm intervals. After a basal 30 min, subjects swallowed a further dose of the scheduled treatment; 60 min later, blood was taken for the determination of plasma cilansetron levels. Thereafter, subjects ingested a 4200 kJ meal and 250 ml sweetened mallow tea (166 kJ); 90 min after meal onset, 1 mg neostigmine was administered intramuscularly and motility recording was continued for 60 min

RESULTS

Phasic contractile activity and intraluminal base-line pressure increased postprandially and more so after neostigmine. With cilansetron, the area under the pressure curve as the primary outcome variable and the number of contractions were significantly greater than with placebo (P = 0.005), amplitude and duration of contractions and base-line pressure were not affected. The effects of the two cilansetron dosages did not differ. With cilansetron, stool tended to become firmer. No adverse effects were observed. Plasma levels were highest with 8 mg cilansetron.

CONCLUSIONS

Cilansetron slightly augments meal-stimulated and markedly neostigmine-stimulated phasic motility of the sigmoid colon. When administered over 7 days, it tends to increase stool consistency and is well tolerated.

Effects of PAF on cardiac function and eicosanoid release in the isolated perfused rat heart: comparison between normotensive and spontaneously hypertensive rats

The aim of this study was (a) in isolated perfused rat heart to characterize the effects of platelet-activating factor (PAF) on coronary flow, ventricular contractility, and eicosanoid release and (b) to determine whether PAF effects are altered in hearts from spontaneously hypertensive rats (SHR). PAF (10(-10)-10(-7) mol) dose-dependently decreased coronary flow and ventricular contractility; concomitantly, coronary effluent concentrations of thromboxane (TX)B2 and prostaglandin F2 alpha (PGF2 alpha) were elevated but not those of prostacyclin. The PAF receptor antagonist WEB 2086 (10(-7)-10(-5) mol/l) concentration-dependently antagonized these PAF effects. In addition; the cyclo-oxygenase inhibitor indomethacin (5 x 10(-5) mol/l) prevented PAF (10(-9)-10(-7) mol) induced eicosanoid release; in the presence of indomethacin PAF caused coronary constriction and ventricular depression only at the highest dose (10(-7) mol) but had no effect at 10(-9) or 10(-8) mol. Moreover, the TXA2 antagonist SQ29,548 (10(-6) mol/l) completely inhibited 10(-8) mol PAF induced ventricular depression but did not effect coronary constriction. In SHR PAF (10(-9)-10(-7) mol) evoked decreases in coronary flow and ventricular contractility did not differ from those in normotensive Wistar-Kyoto rats while PAF induced TXA2 and PGF2 alpha release was markedly enhanced. In addition, decreases in coronary flow and ventricular contractility induced by the TXA2 agonist U 46619 (10(-7) mol/l) were markedly depressed in SHR. We conclude that in isolated perfused rat heart PAF causes coronary constriction and depression of ventricular function mainly indirectly through released TXA2 and/or PGF2 alpha. Moreover, the fact that in SHR the PAF effects on coronary flow and ventricular function are not altered despite markedly enhanced TXA2 and PGF2 alpha release supports the view that in the SHR the receptors mediating TXA2 and/or PGF2 alpha effects are desensitized.

Neonatal pyruvate dehydrogenase deficiency with lipoate responsive lactic acidaemia and hyperammonaemia

A 2-day-old girl developed a severe lactic acidosis with a normal lactate/pyruvate ratio and hyperammonaemia. Plasma arginine and citrulline levels were below the limit of detection. In muscle total pyruvate dehydrogenase complex (PDHC) and pyruvate decarboxylase (E1) activities were reduced to a fraction of lower control values. The acute neonatal period was bridged with peritoneal dialysis, dichloroacetate therapy, supplements of arginine and branched chain amino acids, a complete vitamin B complex and lipoic acid. Lactate homeostasis responded to pharmacological supplements of lipoic acid. At age 1 year the child was hypotonic, showed severe developmental retardation, optic atrophy and cranial dysmorphism. She died aged 1 year 8 months with signs of respiratory paralysis but with normal lactate levels under assisted breathing. Pathological findings at autopsy were suggestive of Leigh syndrome, interstitial pneumonia and extensive fatty infiltration of hepatocytes. Regression analysis of data from 187 plasma amino acid determinations from the patient over a period of 1 year 8 months revealed a persistent-imbalance involving alanine, glutamic acid, glutamine, proline, citrulline and branched chain amino acids. Aspects of acute and long-term therapy in this patient and some implications of the imbalances in plasma amino acids are discussed.

[The effect of trapidil and the trapidil derivative AR 12463 on blood pressure and thromboxane formation in spontaneously hypertensive rats]

The trapidil derivative AR 12463 has a much more stronger inhibiting effect than trapidil on different atherosclerotic parameters of the cell cultures obtained from normal intima and fatty streaks of human aorta, on thromboxane (TX) formation and on the aggregation of human platelets in vitro, and on the activity of phosphodiesterase. In addition to these present results, AR 12463 reduced significantly the mean arterial blood pressure of spontaneously hypertensive rats (at a dosage of 20 mg/kg/d administered orally for 2 weeks) in contrast to the same dosage of trapidil. Simultaneously, TX formation is significantly reduced in serum by 48% in aorta thoracica by 29%, and in aorta abdominalis by 19%. Due to these properties, AR 12463 seems to be suitable for a therapeutic and prophylactic strategy in chronic ischemic diseases.