Implementation of micelle-enabled C(sp2)-C(sp3) cross-electrophile coupling in pharmaceutical synthesis

A sustainable C(sp2)-C(sp3) cross-electrophile coupling was developed between readily available 5-bromophthalide and 1-benzyl-4-iodopiperidine under micellar conditions, leading to a key intermediate of one of our development compounds. Copper was found to play a crucial role as a co-catalyst in this dual catalysis system. The chemistry and process were successfully demonstrated in a kilo scale to deliver sufficient drug substance to the clinical campaigns. This is the first reported scale-up of such a challenging cross-electrophilic coupling that uses an aqueous medium, and not undesirable reprotoxic polar aprotic solvents (e.g. DMF, DMAc, and NMP).

Alkyne metathesis: development of a novel molybdenum-based catalyst system and its application to the total synthesis of epothilone A and C

Sterically hindered molybdenum(III) amido complexes of the general type [Mo[(tBu)(Ar)N]3] (1), upon treatment with CH2Cl2 or other halogen donors, have been converted into highly effective catalysts for all kinds of alkyne metathesis reactions. Although the actual nature of the propagating species formed in situ is still elusive, halogen transfer to the Mo center of 1 plays a decisive role in the activation of such precatalysts. It was possible to isolate and characterize by X-ray crystallography some of the resulting molybdenum halide derivatives such as 15, 16 and 20 which themselves were shown to be catalytically active. Numerous applications illustrate the performance of the catalytic system 1/CH2Cl2 which operates under mild conditions and tolerates an array of polar functional groups. The wide scope allows the method to be implemented into the total synthesis of sensitive and polyfunctional natural products. Most notable among them is a concise entry into the potent anticancer agents epothilone A (86) and C (88). The macrolide core of these targets is forged by ring closing alkyne metathesis (RCAM) of diyne 113, followed by Lindlar hydrogenation of cycloalkyne 114 thus formed. Since this strategy opens a stereoselective entry into (Z)-alkene 115, the approach is inherently more efficient than previous syntheses based on conventional RCM.

Alkyne cross metathesis reactions of extended scope

[figure: see text] A catalyst formed in situ from Mo[N(t-Bu)(Ar)]3 1 (Ar = 3,5-dimethylphenyl) and CH2Cl2 in toluene effects cross metathesis reactions of functionalized alkynes that are beyond reach of more traditional promotors. An application to the synthesis of prostaglandin E2 (PGE2) 19 and the acetylated PGE derivative 18b shows the compatibility of this method with sensitive substrates.

A simultaneous study of the metabolism of apolipoprotein B and albumin in nephrotic patients

BACKGROUND

The nephrotic syndrome is characterized by proteinuria, hypoalbuminemia and hyperlipidemia. Despite intensive research it is not clear at present what the causal links are between these pathological findings.

METHODS

Stable isotope labeled amino acid tracer kinetic analysis was used to simultaneously investigate the metabolism of four apolipoprotein B-containing lipoproteins (VLDL1, VLDL2, IDL and LDL) and albumin in seven patients with nephrotic syndrome and marked hypercholesterolemia, in two additional nephrotic patients with concomitant renal failure and mixed hyperlipidemia, and in a matched group of normolipidemic controls.

RESULTS

Increased concentrations of VLDL2, IDL and LDL were due to (a) impaired VLDL2 and IDL delipidation, (b) reduced LDL catabolism, and (c) a trend towards an increased rate of total apolipoprotein B production. The rate of fractional albumin elimination was three times higher in patients than in controls and the rate of albumin synthesis was increased by 45%. No correlations were detectable between rates of apolipoprotein B production and the rate of albumin synthesis.

CONCLUSIONS

The results of this study suggest that hyperlipidemia in nephrotic syndrome is predominantly the result of delayed lipoprotein delipidation and catabolism. There is no evidence that it is driven by a general increase of the rate of hepatic protein synthesis.

Calcium release-activated calcium current (ICRAC) is a direct target for sphingosine

Whole cell patch-clamp recordings were made to study the regulation of the store-operated calcium release-activated calcium current (ICRAC) by metabolites involved in the sphingomyelin pathway in RBL-2H3 cells. Sphingosine, a regulator of cell growth, inhibits ICRAC completely within 200 s and independently from conversion to either sphingosine 1-phosphate or ceramide. Structural analogs of sphingosine, including N,N-dimethylsphingosine, DL-threo-dihydrosphingosine, and N-acetylsphingosine (C2-ceramide) also block ICRAC. This effect is always accompanied by an elevation of whole cell membrane capacitance. These sphingolipids appear, therefore, to accumulate in the plasma membrane and directly block ICRAC channels. Sphingosylphosphorylcholine also increases capacitance but does not inhibit ICRAC, demonstrating structural specificity and that the elevation of capacitance is necessary but not sufficient for block. Nerve growth factor, which is known to break down sphingomyelin, inhibits ICRAC, and this inhibition can be antagonized by reducing sphingosine production with L-cycloserine, suggesting that ICRAC is a physiologically relevant and direct target of sphingosine. We propose that sphingosine directly blocks ICRAC, suggesting that the sphingomyelin pathway is involved in ICRAC regulation.

Effects of anti-C5a monoclonal antibodies on oxygen use in a porcine model of severe sepsis

METHODS

We analysed the effects of complement depletion and of C5a inhibition on haemodynamic parameters, oxygen delivery (DO2), oxygen consumption (VO2), oxygen extraction ratio (OER) and blood lactate levels after live bacteria infusion in pigs.

RESULTS

In the first series of experiments, animals were decomplemented by cobra venom factor (CVF, 125 micrograms kg-1) and challenged with 1.3 x 10(9) Escherichia coli kg-1. In a second series, animals were treated with neutralizing anti-C5a monoclonal antibodies (mAb) T13/9 before infusion of an increased E. coli dosage (1 x 10(10) E. coli kg-1). Administration of Gram-negative bacteria resulted in hypotension, tachycardia, pulmonary hypertension and decreased cardiac output typical for severe sepsis. These alterations were more pronounced in animals challenged with a higher bacteria concentration (1 x 10(10) E. coli kg-1, n = 5) than with a lower dosage (1.3 x 10(9) E. coli kg-1, n = 4). Complement depletion by CVF injection 24 h before E. coli infusion (n = 4), or anti-C5a mAb T13/9 administration (n = 4) had no effect on the changes in haemodynamic parameters and in DO2 associated with E. coli challenge. Application of either 1.3 x 10(9) or 1 x 10(10) E. coli kg-1 resulted in a marked decrease in VO2 and an increase in blood lactate levels, whereas the OER did not change throughout the experiment. In contrast, pretreatment with CVF 24 h before low-dose E. coli (1.3 x 10(9) kg-1) administration resulted in a significant increase in VO2 (P < 0.05) and in OER (P < 0.05) compared with untreated septic animals (n = 4). No hyperlactaemia occurred in complement-depleted septic animals compared with complement-sufficient animals (P < 0.05). Animals challenged with a high E. coli dose (1 x 10(1) kg-1) and treated with anti-C5a mAbs showed a pronounced increase in VO2 and OER (P < 0.05) accompanied by an attenuated increase in lactate levels (P < 0.05) compared with untreated septic animals.

CONCLUSION

The results demonstrate an improved oxygen use after complement depletion in this model of severe Gram-negative sepsis. Furthermore, a similar effect was seen after specifically neutralizing C5a by mAbs, indicating a role of C5a in the underlying mechanism.

Fast inactivation of delayed rectifier K conductance in squid giant axon and its cell bodies

Inactivation of delayed rectifier K conductance (gk) was studied in squid giant axons and in the somata of giant fiber lobe (GFL) neurons. Axon measurements were made with an axial wire voltage clamp by pulsing to VK (approximately -10 mV in 50-70 mM external K) for a variable time and then assaying available gK with a strong, brief test pulse. GFL cells were studied with whole-cell patch clamp using the same prepulse procedure as well as with long depolarizations. Under our experimental conditions (12-18 degrees C, 4 mM internal MgATP) a large fraction of gK inactivates within 250 ms at -10 mV in both cell bodies and axons, although inactivation tends to be more complete in cell bodies. Inactivation in both preparations shows two kinetic components. The faster component is more temperature-sensitive and becomes very prominent above 12 degrees C. Contribution of the fast component to inactivation shows a similar voltage dependence to that of gK, suggesting a strong coupling of this inactivation path to the open state. Omission of internal MgATP or application of internal protease reduces the amount of fast inactivation. High external K decreases the amount of rapidly inactivating IK but does not greatly alter inactivation kinetics. Neither external nor internal tetraethylammonium has a marked effect on inactivation kinetics. Squid delayed rectifier K channels in GFL cell bodies and giant axons thus share complex fast inactivation properties that do not closely resemble those associated with either C-type or N-type inactivation of cloned Kvl channels studied in heterologous expression systems.

The nitric oxide/cGMP pathway couples muscarinic receptors to the activation of Ca2+ influx

Inward currents activated by 8-bromc-cGMP and by muscarinic agonist were compared in N1E-115 mouse neuroblastoma cells using perforated-patch voltage clamp and Fura-2 imaging. The cGMP analog activates a voltage-independent inward current that is carried at least in part by Ca2+ because it persists in Na(+)-free saline when Ca2+ is present and is blocked by external Mn2+ and Ba2+. The current is similar to the inward current that develops during stimulation of M1 muscarinic receptors, and the currents activated by agonist and by 8-bromo-cGMP are not additive, indicating that the same pathway is involved. Inhibition of cGMP production with NG-monomethyl-L-arginine (L-NMMA), a competitive inhibitor of nitric oxide (NO)-synthase, prevents activation of Ca2+ current by agonist without affecting the content of intracellular Ca2+ stores or the ability of agonist to mobilize Ca2+. The inhibition is overcome by 8-bromo-cGMP. LY83583, a competitive inhibitor of guanylyl cyclase, reversibly blocks activation of Ca2+ current by agonist, again without affecting the content of Ca2+ stores or Ca2+ release. Rp-8-pCPT-cGMPS, an inhibitory analog of cGMP, also reduces the Ca2+ current and reduces Ca2+ influx during muscarinic activation. It is concluded that cGMP is the necessary and sufficient intermediate in the pathway linking muscarinic receptor occupancy to the activation of voltage-independent Ca2+ current. The pathway involves positive feedback. Calcium entering via voltage-independent channels preferentially stimulates NO-synthase, which leads to enhanced cGMP production and greater Ca2+ influx. Positive feedback may explain the rapid increase in cGMP that occurs during muscarinic receptor activation.

The relationship between depletion of intracellular Ca2+ stores and activation of Ca2+ current by muscarinic receptors in neuroblastoma cells

The relationship between the depletion of IP3-releasable intracellular Ca2+ stores and the activation of Ca(2+)-selective membrane current was determined during the stimulation of M1 muscarinic receptors in N1E-115 neuroblastoma cells. External Ca2+ is required for refilling Ca2+ stores and the voltage-independent, receptor-regulated Ca2+ current represents a significant Ca2+ source for refilling. The time course of Ca2+ store depletion was measured with fura-2 fluorescence imaging, and it was compared with the time course of Ca2+ current activation measured with nystatin patch voltage clamp. At the time of maximum current density (0.18 + .03 pA/pF; n = 48), the Ca2+ content of the IP3-releasable Ca2+ pool is reduced to 39 + 3% (n = 10) of its resting value. Calcium stores deplete rapidly, reaching a minimum Ca2+ content in 15-30 s. The activation of Ca2+ current is delayed by 10-15 s after the beginning of Ca2+ release and continues to gradually increase for nearly 60 s, long after Ca2+ release has peaked and subsided. The delay in the appearance of the current is consistent with the idea that the production and accumulation of a second messenger is the rate-limiting step in current activation. The time course of Ca2+ store depletion was also measured after adding thapsigargin to block intracellular Ca2+ ATPase. After 15 min in thapsigargin, IP3-releasable Ca2+ stores are depleted by > 90% and the Ca2+ current is maximal (0.19 + 0.05 pA/pF; n = 6). Intracellular loading with the Ca2+ buffer EGTA/AM (10 microM; 30 min) depletes IP3-releasable Ca2+ stores by between 25 and 50%, and it activates a voltage-independent inward current with properties similar to the current activated by agonist or thapsigargin. The current density after EGTA/AM loading (0.61 + 0.32 pA/pF; n = 4) is three times greater than the current density in response to agonist or thapsigargin. This could result from partial removal of Ca(2+)-dependent inactivation.

Calcium requirement for cGMP production during muscarinic activation of N1E-115 neuroblastoma cells

Muscarinic agonists elicit large increases in intracellular Ca2+ and guanosine 3',5'-cyclic monophosphate (cGMP) in N1E-115 neuroblastoma cells. Both signals are blocked in cells loaded with the Ca2+ buffer 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid showing that the increase in intracellular Ca2+ concentration ([Ca2+]i) is necessary to stimulate cGMP accumulation. Inhibition of nitric oxide synthase (NOS) blocks the cGMP response without affecting the peak amplitude of the intracellular Ca2+ signal, and it is concluded that Ca(2+)-dependent activation of NOS is required for cGMP production. cGMP accumulation is reduced by 60% when cells are bathed in Ca(2+)-free saline, but the peak change in [Ca2+]i is not affected. This suggests that Ca2+ influx is strongly coupled to the activation of cGMP production, even though it makes a smaller contribution to the intracellular Ca2+ signal than does Ca2+ release. Thapsigargin, which releases Ca2+ from intracellular stores, activates Ca2+ influx and increases cGMP. The cGMP increase is transient and follows approximately the same time course as Ca2+ store depletion. Ca2+ influx remains activated after store depletion, however, which indicates that influx alone cannot sustain cGMP production. It is concluded that summation of Ca2+ influx and Ca2+ release is necessary to reach a threshold Ca2+ level needed to stimulate cGMP accumulation. Because of the large contribution from Ca2+ influx, we suggest that NOS or a cofactor necessary for its activation may be located close to Ca2+ channels in the membrane.

Calcium current activated by muscarinic receptors and thapsigargin in neuronal cells

The activation of muscarinic receptors in N1E-115 neuroblastoma cells elicits a voltage-independent calcium current. The current turns on slowly, reaches its maximum value approximately 45 s after applying the agonist, is sustained as long as agonist is present, and recovers by one half in approximately 10 s after washing the agonist away. The current density is 0.11 +/- 0.08 pA/pF (mean +/- SD; n = 12). It is absent in zero-Ca++ saline and reduced by Mn++ and Ba++. The I(V) curve characterizing the current has an extrapolated reversal potential > +40 mV. The calcium current is observed in cells heavily loaded with BAPTA indicating that the calcium entry pathway is not directly gated by calcium. In fura-2 experiments, we find that muscarinic activation causes an elevation of intracellular Ca++ that is due to both intracellular calcium release and calcium influx. The component of the signal that requires external Ca++ has the same time course as the receptor operated calcium current. Calcium influx measured in this way elevates (Ca++)i by 89 +/- 41 nM (n = 7). Thapsigargin, an inhibitor of Ca++/ATPase associated with the endoplasmic reticulum (ER), activates a calcium current with similar properties. The current density is 0.22 +/- 0.20 pA/pF (n = 6). Thapsigargin activated current is reduced by Mn++ and Ba++ and increased by elevated external Ca++. Calcium influx activated by thapsigargin elevates (Ca++)i by 82 +/- 35 nM. The Ca++ currents due to agonist and due to thapsigargin do not sum, indicating that these procedures activate the same process. Carbachol and thapsigargin both cause calcium release from internal stores and the calcium current bears strong similarity to calcium-release-activated calcium currents in nonexcitable cells (Hoth, M., and R. Penner. 1993. Journal of Physiology. 465:359-386; Zweifach, A., and R. S. Lewis, 1993. Proceedings of the National Academy of Sciences, USA. 90:6295-6299).

Membrane toxicity of the protein kinase C inhibitor calphostin A by a free-radical mechanism

The effects of calphostin A on cytoplasmic calcium levels, receptor-mediated calcium release, and membrane input resistance were measured in neuroblastoma cells. Calphostin A is a lipophilic, light-sensitive perylenequinone that generates singlet oxygen when illuminated. It inhibits the activity of protein kinase C (IC50 = 250 nM), but only in the presence of light. Phorbol esters normally attenuate carbachol-evoked calcium release. This effect was blocked by simultaneous exposure to light and calphostin A (40 nM) for 30 min. At higher doses (0.5-1 microM) calphostin A also approximately doubled the resting calcium level and decreased cell input resistance by 51%. These toxic effects did not occur in the dark or after preincubation with the antioxidant alpha-tocopherol. These data support the hypothesis that the calphostins act by partitioning into the membrane and producing singlet oxygen and endoperoxides which then irreversibly modify protein kinase C and other membrane proteins and lipids.

Membrane toxicity of the protein kinase C inhibitor calphostin A by a free-radical mechanism

The effects of calphostin A on cytoplasmic calcium levels, receptor-mediated calcium release, and membrane input resistance were measured in neuroblastoma cells. Calphostin A is a lipophilic, light-sensitive perylenequinone that generates singlet oxygen when illuminated. It inhibits the activity of protein kinase C (IC50 = 250 nM), but only in the presence of light. Phorbol esters normally attenuate carbachol-evoked calcium release. This effect was blocked by simultaneous exposure to light and calphostin A (40 nM) for 30 min. At higher doses (0.5-1 microM) calphostin A also approximately doubled the resting calcium level and decreased cell input resistance by 51%. These toxic effects did not occur in the dark or after preincubation with the antioxidant alpha-tocopherol. These data support the hypothesis that the calphostins act by partitioning into the membrane and producing singlet oxygen and endoperoxides which then irreversibly modify protein kinase C and other membrane proteins and lipids.

Intracellular calcium release in N1E-115 neuroblastoma cells is mediated by the M1 muscarinic receptor subtype and is antagonized by McN-A-343

Experiments using muscarinic receptor antagonists were done to determine which muscarinic receptor subtypes(s) mediate carbachol-evoked calcium release in N1E-115 cells. McN-A-343 and a new analog, (+/-)BN228, were weak antagonists and neither compound caused release on its own. The rank order of potency was 4-DAMP greater than pirenzepine greater than AFDX116 greater than (+/-)BN228 and McN-A-343. This profile, pirenzepine's high potency (19-fold greater than AFDX116) and its IC50 of 31 nM suggest that calcium release in this neuronal cell line is mediated by the M1 muscarinic receptor subtype.

Sodium current and membrane potential in EDL muscle fibers from normal and dystrophic (mdx) mice

The macroscopic and single-channel properties of sodium currents and membrane potential were studied in intact extensor digitorum longus (EDL) muscle fibers from mdx (C57BL/10ScSn-mdx) and normal (C57BL/10SnJ) mice. The voltage dependence of activation and inactivation were determined and the associated gating charges were calculated to determine if the lack of dystrophin associated with the mdx condition has any influence on sodium channels either directly or by effects on the membrane environment of the channel. Sodium currents were recorded from cell-attached patches on EDL muscle fibers isolated by collagenase treatment and manual dissection. Both macroscopic and single-channel currents were studied. We found no apparent difference in the sodium channel properties from the two types of muscle. In addition, microelectrode measurements in both mdx and normal muscle fibers indicated similar resting membrane potentials (Vm around -95 mV), which suggests that the normal behavior of sodium channels in the muscle sarcolemma is unaffected by the X-linked gene defect.