Carboxylation and decarboxylation of active site Lys 84 controls the activity of OXA-24 ß-lactamase of Acinetobacter baumannii: Raman crystallographic and solution evidence.

The class D ß-lactamases are characterized by the presence of a carboxylated lysine in the active site that participates in catalysis. Found in Acinetobacter baumannii, OXA-24 is a class D carbapenem hydrolyzing enzyme that exhibits resistance to most available ß-lactamase inhibitors. In this study, the reaction between a 6-alkylidiene penam sulfone inhibitor, SA-1-204, in single crystals of OXA-24 is followed by Raman microscopy. Details of its reaction with SA-1-204 provide insight into the enzyme's mode of action and help define the mechanism of inhibition. When the crystal is maintained in HEPES buffer, the reaction is fast, shorter than the time scale of the Raman experiment. However, when the crystal holding solution contains 28% PEG 2000, the reaction is slower and can be recorded by Raman microscopy in real time; the inhibitor's Raman bands quickly disappear, transient features are seen due to an early intermediate, and, at approximately 2-11 min, new bands appear that are assigned to the late intermediate species. At about 50 min, bands due to all intermediates are replaced by Raman signals of the unreacted inhibitor. The new population remains unchanged indicating (i) that the OXA-24 is no longer active and (ii) that the decarboxylation of Lys84 occurred during the first reaction cycle. Using absorbance spectroscopy, a one-cycle reaction could be carried out in aqueous solution producing inactive OXA-24 as assayed by the chromogenic substrate nitrocefin. However, activity could be restored by reacting aqueous OXA-24 with a large excess of NaHCO(3), which recarboxylates Lys84. In contrast, the addition of NaHCO(3) was not successful in reactivating OXA-24 in the crystalline state; this is ascribed to the inability to create a concentration of NaHCO(3) in large excess over the OXA-24 that is present in the crystal. The finding that inhibitor compounds can inactivate a class D enzyme by promoting decarboxylation of an active site lysine suggests a novel function that could be exploited in inhibitor design.

Regulation of leucine catabolism by metabolic fuels in mammary epithelial cells.

Lactation is associated with elevated catabolism of branched-chain amino acids (BCAA) in mammary glands to produce glutamate, glutamine, alanine, aspartate, and asparagine. This study determined effects of metabolic fuels on the catabolism of leucine (a representative BCAA) in bovine mammary epithelial cells. Cells were incubated at 37 °C for 2 h in Krebs buffer containing 0.5 mM L-leucine and either L-[1-(14)C]leucine or L-[U-(14)C]leucine. The medium also contained 0-5 mM D-glucose, 0-2 mM L-glutamine, 0-4 mM DL-ß-hydroxybutyrate, or 0-2 mM oleic acid. Rates of leucine decarboxylation were 60 % lower, but rates of α-ketoisocaproate production were 34 % higher, in the presence of 2 mM glucose than in its absence. All variables of leucine catabolism did not differ between 2 and 5 mM glucose or between 0 and 4 mM DL-ß-hydroxybutyrate. Compared with 0-0.25 mM glutamine, 0.5 and 2 mM L-glutamine reduced leucine transport, transamination, and decarboxylation. In contrast, increasing the concentration of oleic acid from 0 to 2 mM dose-dependently stimulated leucine transamination, decarboxylation, and oxidation of carbons 2-6. Oleic acid also enhanced the abundance of cytosolic BCAA transaminase, while reducing the phosphorylated level (inactive state) of the E1α subunit of the mitochondrial branched-chain α-ketoacid dehydrogenase complex. Thus, hypoglycemia or ketosis in early lactation does not likely affect BCAA metabolism in mammary epithelial cells. Increasing circulating levels of BCAA and oleic acid may have great potential to increase the syntheses of glutamate, glutamine, aspartate, alanine, and asparagine by lactating mammary glands, thereby leading to enhanced production of milk for suckling neonates.

Structural and mechanistic studies on Klebsiella pneumoniae 2-Oxo-4-hydroxy-4-carboxy-5-ureidoimidazoline decarboxylase.

The stereospecific oxidative degradation of uric acid to (S)-allantoin was recently shown to proceed via three enzymatic steps. The final conversion is a decarboxylation of the unstable intermediate 2-oxo-4-hydroxy-4-carboxy-5-ureidoimidazoline (OHCU) and is catalyzed by OHCU decarboxylase. Here we present the structures of Klebsiella pneumoniae OHCU decarboxylase in unliganded form and with bound allantoin. These structures provide evidence that ligand binding organizes the active site residues for catalysis. Modeling of the substrate and intermediates provides additional support for this hypothesis. In addition we characterize the steady state kinetics of this enzyme and report the first OHCU decarboxylase inhibitor, allopurinol, a structural isomer of hypoxanthine. This molecule is a competitive inhibitor of K. pneumoniae OHCU decarboxylase with a K(i) of 30 ± 2 µM. Circular dichroism measurements confirm structural observations that this inhibitor disrupts the necessary organization of the active site. Our structural and biochemical studies also provide further insights into the mechanism of catalysis of OHCU decarboxylation.

Branched-chain amino acid metabolon: interaction of glutamate dehydrogenase with the mitochondrial branched-chain aminotransferase (BCATm).

The catabolic pathway for branched-chain amino acids includes deamination followed by oxidative decarboxylation of the deaminated product branched-chain alpha-keto acids, catalyzed by the mitochondrial branched-chain aminotransferase (BCATm) and branched-chain alpha-keto acid dehydrogenase enzyme complex (BCKDC). We found that BCATm binds to the E1 decarboxylase of BCKDC, forming a metabolon that allows channeling of branched-chain alpha-keto acids from BCATm to E1. The protein complex also contains glutamate dehydrogenase (GDH1), 4-nitrophenylphosphatase domain and non-neuronal SNAP25-like protein homolog 1, pyruvate carboxylase, and BCKDC kinase. GDH1 binds to the pyridoxamine 5'-phosphate (PMP) form of BCATm (PMP-BCATm) but not to the pyridoxal 5'-phosphate-BCATm and other metabolon proteins. Leucine activates GDH1, and oxidative deamination of glutamate is increased further by addition of PMP-BCATm. Isoleucine and valine are not allosteric activators of GDH1, but in the presence of 5'-phosphate-BCATm, they convert BCATm to PMP-BCATm, stimulating GDH1 activity. Sensitivity to ADP activation of GDH1 was unaffected by PMP-BCATm; however, addition of a 3 or higher molar ratio of PMP-BCATm to GDH1 protected GDH1 from GTP inhibition by 50%. Kinetic results suggest that GDH1 facilitates regeneration of the form of BCATm that binds to E1 decarboxylase of the BCKDC, promotes metabolon formation, branched-chain amino acid oxidation, and cycling of nitrogen through glutamate.

Thiamine supplementation in the critically ill.

PURPOSE OF REVIEW: To summarize the properties of thiamine and evaluate current evidence on thiamine status and supplementation, for different populations of critically ill patients. RECENT FINDINGS: Thiamine, in the form of thiamine pyrophosphate, is a critical co-factor in the glyocolysis and oxidative decarboxylation of carbohydrates for energy production. Different studies have shown that critical illness in adults and children is characterized by absolute or relative thiamine depletion, which is associated with an almost 50% increase in mortality. Thiamine deficiency should be suspected in different clinical scenarios such as severe sepsis, burns, unexplained heart failure or lactic acidosis, neurological disorder in patients with previous history of alcoholism, starvation, chronic malnutrition, long-term parenteral feeding, hyperemesis gravidarum, or bariatric surgery. Nonetheless, thiamine supplements are not routinely given to critically ill patients. Clinicians should be able to suspect and recognize risk factors for the occurrence of severe neurological disorders secondary to thiamine deficiency, as early treatment can prevent the appearance of permanent neurological damage. SUMMARY: Symptoms and signs associated with thiamine deficiency lack sensitivity and specificity in critically ill patients. Consequently, depletion is frequently unrecognized and underdiagnosed by clinicians. Potentially deleterious consequences of thiamine depletion should be avoided by early and appropriate supplementation.

Discovery and inhibition of an interspecies gut bacterial pathway for Levodopa metabolism.

The human gut microbiota metabolizes the Parkinson's disease medication Levodopa (l-dopa), potentially reducing drug availability and causing side effects. However, the organisms, genes, and enzymes responsible for this activity in patients and their susceptibility to inhibition by host-targeted drugs are unknown. Here, we describe an interspecies pathway for gut bacterial l-dopa metabolism. Conversion of l-dopa to dopamine by a pyridoxal phosphate-dependent tyrosine decarboxylase from Enterococcus faecalis is followed by transformation of dopamine to m-tyramine by a molybdenum-dependent dehydroxylase from Eggerthella lenta These enzymes predict drug metabolism in complex human gut microbiotas. Although a drug that targets host aromatic amino acid decarboxylase does not prevent gut microbial l-dopa decarboxylation, we identified a compound that inhibits this activity in Parkinson's patient microbiotas and increases l-dopa bioavailability in mice.

Induction of dopamine biosynthesis by l-DOPA in PC12 cells: implications of L-DOPA influx and cyclic AMP.

The effects of 3,4-dihydroxyphenylalanine (l-DOPA) on dopamine biosynthesis and cytotoxicity were investigated in PC12 cells. l-DOPA treatment (20-200 microM) increased the levels of dopamine by 226%-504% after 3-6 h of treatment and enhanced the activities of tyrosine hydroxylase (TH) and aromatic l-amino acid decarboxylase (AADC). l-DOPA (20-200 muM) treatment led to a 562%-937% increase in l-DOPA influx at 1 h, which inhibited the activity of TH, but not AADC, during the same period. The extracellular releases of dopamine were also increased by 231%-570% after treatment with 20 and 200 microM l-DOPA for 0.5-3 h. l-DOPA at a concentration of 100-200 microM, but not 20 microM, exerted apoptotic cytotoxicity towards PC12 cells for 24-48 h. l-DOPA (20-200 microM) increased the intracellular cyclic AMP levels by 318%-557% after 0.5-1 h in a concentration-dependent manner. However, the elevated cyclic AMP levels by l-DOPA could not protect against l-DOPA (100-200 microM)-induced cytotoxicity after 24-48 h. In addition, l-DOPA (20-200 microM)-induced increases in cyclic AMP and dopamine were significantly reduced by treatment with SCH23390 (dopamine D(1) receptor antagonist). The increased levels of dopamine by l-DOPA were also reduced by H89 (protein kinase A, PKA, inhibitor) and GF109203X (protein kinase C inhibitor); however, the reduction by GF109203X was not significant. l-DOPA at 20-200 microM stimulated the phosphorylation of PKA and cyclic AMP-response element binding protein and induced the biosynthesis of the TH protein. These results indicate that 20-200 microM l-DOPA induces dopamine biosynthesis by two pathways. One pathway involves l-DOPA directly entering the cells to convert dopamine through AADC activity (l-DOPA decarboxylation). The other pathway involves l-DOPA and/or released dopamine activating TH to enhance dopamine biosynthesis by the dopamine D(1) receptor-cyclic AMP-PKA signaling system (dopamine biosynthesis by TH).

Multiple modes of inhibition of human cytochrome P450 2J2 by dronedarone, amiodarone and their active metabolites.

Dronedarone, a multiple ion channel blocker is prescribed for the treatment of paroxysmal and persistent atrial fibrillation. While dronedarone does not precipitate toxicities like its predecessor amiodarone, its clinical use has been associated with idiosyncratic hepatic and cardiac adverse effects and drug-drug interactions (DDIs). As dronedarone is a potent mechanism-based inactivator of CYP3A4 and CYP3A5, a question arose if it exerts a similar inhibitory effect on CYP2J2, a prominent cardiac CYP450 enzyme. In this study, we demonstrated that CYP2J2 is reversibly inhibited by dronedarone (Ki=0.034 µM), amiodarone (Ki=4.8µM) and their respective pharmacologically active metabolites namely N-desbutyldronedarone (NDBD) (Ki=0.55 µM) and N-desethylamiodarone (NDEA) (Ki=7.4 µM). Moreover, time-, concentration- and NADPH-dependent irreversible inactivation of CYP2J2 was investigated where inactivation kinetic parameters (KI, kinact) and partition ratio (r) of dronedarone (0.05 µM, 0.034 min(-1), 3.3), amiodarone (0.21 µM, 0.015 min(-1), 20.7) and NDBD (0.48 µM, 0.024 min(-1), 21.7) were observed except for NDEA. The absence of the characteristic Soret peak, lack of recovery of CYP2J2 activity upon dialysis, and biotransformation of dronedarone and NDBD to quinone-oxime reactive metabolites further confirmed the irreversible inactivation of CYP2J2 by dronedarone and NDBD is via the covalent adduction of CYP2J2. Our novel findings illuminate the possible mechanisms of DDIs and cardiac adverse effects due to both reversible inhibition and irreversible inactivation of CYP2J2 by dronedarone, amiodarone and their active metabolites.

Arginine decarboxylase: A novel biological target of mercury compounds identified in PC12 cells.

Mercury compounds are well-known toxic environmental pollutants and potently induce severe neurotoxicological effects in human and experimental animals. Previous studies showed that one of the mechanisms of mercury compounds neurotoxicity arose from the over-activation of the N-methyl d-aspartate (NMDA)-type glutamate receptor induced by increased glutamate release. In this work, we aimed to investigate the molecular mechanisms of Hg compounds neurotoxicities by identifying their biological targets in cells. Firstly, the inhibitory effects of four Hg compounds, including three organic (methyl-, ethyl- and phenyl-mercury) and one inorganic (Hg2+) Hg compounds, on the activity of arginine decarboxylase (ADC), a key enzyme in the central agmatinergic system, were evaluated. They were found to inhibit the ADC activity significantly with methylmercury (MeHg) being the strongest (IC50=7.96nM). Furthermore, they showed remarkable inhibitory effects on ADC activity in PC12 cells (MeHg>EtHg>PhHg>HgCl2), and led to a marked loss in the level of agmatine, an endogenous neuromodulatory and neuroprotective agent that selectively blocks the activation of NMDA receptors. MeHg was detected in the immunoprecipitated ADC from the cells, providing unequivocal evidence for the direct binding of MeHg with ADC in the cell. Molecular dynamics simulation revealed that Hg compounds could form the coordination bond not only with cofactor PLP of ADC, but also with substrate arginine. Our finding indicated that MeHg could attenuate the neuroprotective effects of agmatine by the inhibition of ADC, a new cellular target of MeHg, which might be implicated in molecular mechanism of MeHg neurotoxicity.

NADPH activates a decarboxylation reaction catalysed by lamb liver 6-phosphogluconate dehydrogenase.

NADP-dependent lamb liver 6-phosphogluconate dehydrogenase catalyses the oxidative decarboxylation of 2-deoxy-6-phosphogluconate, an analogue of the natural substrate. The first products of the reaction are NADPH and 3-keto-2-deoxy-6-phosphogluconate. The NADPH, released from the enzyme, binds to the coenzyme site of the same or the other subunit, activating the decarboxylation reaction in which has not a redox role, since it can be substituted by an analogue devoid of enzymatic redox power. These findings are compared to those obtained with other NADP-dependent decarboxylating dehydrogenases.

CD95 (Fas/APO-1) induces an increased phosphatidylserine synthesis that precedes its externalization during programmed cell death.

CD95 (Fas, APO-1)-induced programmed cell death (apoptosis) in T cell lines is accompanied by a rapid flip-flop of phosphatidylserine (PtdSer). Externalization of this phospholipid has been previously recognized as one of the early detectable events of cells undergoing apoptosis. We show here that CD95 induces a rapid (detectable at time < 15 min), strong (2.5-fold) but transitory neosynthesis of PtdSer in the Jurkat cell line that precedes its externalization. PtdSer decarboxylation, a mitochondrial specific process, was strongly inhibited by CD95 suggesting that changes in mitochondrial activity take place in the early events of Fas-induced apoptosis and participate in the increased PtdSer synthesis observed. In cells undergoing apoptosis, newly synthesized PtdSer first exposed at the cell surface was in part shed with CD95-induced plasma membrane vesicles, a process that likely explains the transitory effect observed.

Leptin inhibits insulin-stimulated incorporation of glucose into lipids and stimulates glucose decarboxylation in isolated rat adipocytes.

Leptin is an adipocyte hormone involved in the regulation of energy homeostasis. Generally accepted biological effects of leptin are inhibition of food intake and stimulation of metabolic rate in ob/ob mice, that are defective in the leptin gene. In contrast to these centrally mediated effects of leptin, we are reporting here on leptin effects on glucose incorporation into lipids and glucose decarboxylation in adipocytes isolated from male lean albino rats. Adipocytes previously cultivated (15 h) in the presence of leptin presented a 25% (P < 0.05) reduction of the insulin stimulated incorporation of glucose into lipids. Concurrently, the basal conversion of (U-14C)D-glucose into 14CO2 increased (110%) in the leptin cultivated adipocytes and reached values (1.54 nmol/10(5) cells) similar to the insulin stimulated group (not cultivated with leptin) (1.40 nmol/10(5) cells). In addition, in the presence of insulin, the leptin cultivated adipocytes elicited a 162% (P < 0.05) increase in 14CO2 production that was significantly higher than the increase observed for the not-leptin-cultivated insulin group (92%). We conclude that leptin: 1) directly inhibits the insulin stimulated glucose incorporation into lipids; 2) stimulates glucose decarboxylation, and also potentiates the effect of insulin on glucose decarboxylation in isolated adipocytes. Leptin per se does not alter glucose incorporation into lipids.

Defective 3,4-dihydroxyphenylalanine decarboxylation to dopamine in hydralazine-treated hypertensive patients may be pyridoxine remediable.

The previously observed defective dopamine (DA) generation from 3,4-dihydroxyphenylalanine (DOPA) can also be seen in patients treated for many years by hydralazine. This may be due to a hydralazine-induced depletion of pyridoxine, an essential coenzyme of the aromatic L-amino acid decarboxylase (LAAD). Eleven hydralazine-treated stable essential hypertensive (EH) patients, initially found to have a defect in the DOPA decarboxylation to DA, tested by a single DOPA administration (500 mg, orally), were retested by the same test 4 days after pyridoxine pretreatment (100 mg/day) for data on blood pressure (BP), pulse rate, and renal and plasma catecholamines and their metabolites, as well as plasma atrial natriuretic factor (ANF), cyclic GMP (cGMP), plasma renin activity (PRA), and plasma aldosterone (PA). Initially, hydralazine-treated stable EH patients manifested, following DOPA administration, lower DOPA decarboxylation to DA than control subjects. Pyridoxine pretreatment accelerated DA generation from exogenous DOPA and attenuated the DOPA-induced increases in plasma and urinary DOPA and its metabolite 3-O-methyl-DOPA, but accentuated the increase in free DA and its main metabolites, dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), while BP, ANF, cGMP, PRA, and PA remained unaffected. The DOPA-induced increments of urinary DA were, in contrast to plasma DA changes, blunted by pyridoxine pretreatment. The attenuation of the sodium excretion by pyridoxine pretreatment exceeded that of the DA excretion, suggesting that pyridoxine suppressed a natriuretic factor, other than ANF, or activated a sodium-retaining factor, other than renin or aldosterone.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of L-aspartate 4-carboxy-lyases of Cunninghamella elegans and Penicillium citrinum.

L-Aspartate 4-carboxy-lyase of Cunninghamella elegans and Penicillium citrinum has a pH optimum of 5.5. Maximal activity of both enzymes is obtained at 40 degrees C, and both are thermolabile. The Km of the C. elegans enzyme for L-aspartate is 25 mM, while that of the P. citrinum enzyme is 27 mM. The two enzymes are specific for L-aspartate. They are activated by pyridoxal 5-phosphate and a number of alpha-keto acids. The catalytic activity of both enzymes is stimulated by Co2+, Fe2+, Ni2+ and Mn2+ ions and inhibited by Zn2+ and Cu2+. Inhibition by iodoacetate and activation by SH-compounds suggest that sulfhydryl groups may participate in enzyme activity.

[Inactivation of yeast pyruvate decarboxylase in the presence of substrate and quinone electron acceptors]. / Inaktivatsiia drozhzhevoi piruvatdekarboksilazy v prisutstvii substrata i khinonovykh aktseptorov élektronov.

The rate constants of paracatalytic inactivation of pyruvate decarboxylase in the presence of 1,4-naphthoquinones and 1,4-benzoquinones are determined by redox potentials of the oxidant. The logarithm of k2 depends hyperbolically on the redox potential of quinone E0(Q/Q-.) with the coefficient of proportionality which approximates 8.4, The absence of considerable deviations in this correlation for the oxidants of different structures with closed values Eo(Q/Q-.) indicates that the enzyme produces no additional steric barrier.

Metabolic engineering of Candida glabrata for diacetyl production.

In this study, Candida glabrata, an efficient pyruvate-producing strain, was metabolically engineered for the production of the food ingredient diacetyl. A diacetyl biosynthetic pathway was reconstructed based on genetic modifications and medium optimization. The former included (i) channeling carbon flux into the diacetyl biosynthetic pathway by amplification of acetolactate synthase, (ii) elimination of the branched pathway of α-acetolactate by deleting the ILV5 gene, and (iii) restriction of diacetyl degradation by deleting the BDH gene. The resultant strain showed an almost 1∶1 co-production of α-acetolactate and diacetyl (0.95 g L(-1)). Furthermore, addition of Fe3+ to the medium enhanced the conversion of α-acetolactate to diacetyl and resulted in a two-fold increase in diacetyl production (2.1 g L(-1)). In addition, increased carbon flux was further channeled into diacetyl biosynthetic pathway and a titer of 4.7 g L(-1) of diacetyl was achieved by altering the vitamin level in the flask culture. Thus, this study illustrates that C. glabrata could be tailored as an attractive platform for enhanced biosynthesis of beneficial products from pyruvate by metabolic engineering strategies.

Purification and properties of malic enzyme from herring Clupea harengus spermatozoa.

Herring spermatozoa exhibit higher activity of malic enzyme (ME) than Atlantic salmon (Salmo salar), brown trout (Salmo trutta), carp (Cyprinus carpio) and African catfish (Clarias gariepinus) spermatozoa. Two molecular forms of ME are present in herring spermatozoa: an NAD-preferring malic enzyme with very high activity and an NADP-specific malic enzyme with much lower activity (ratio about 33:1). NAD-preferring ME was purified by chromatography on DEAE-Sepharose, Red Agarose and Sephadex G-200 to a specific activity of 36 µmol/min/mg protein and NADP-specific ME on DEAE-Sepharose and 2'5'-ADP Sepharose. The molecular mass for NAD-preferring and NADP-specific ME determined by SDS-PAGE was equal to 61 and 64 kDa, respectively. High activity of ME suggests adaptation of herring spermatozoa to metabolism at high oxygen tension for herring spawn.

Effects of adrenergic agents on intracellular Ca2+ homeostasis and metabolism of glucose in astrocytes with an emphasis on pyruvate carboxylation, oxidative decarboxylation and recycling: implications for glutamate neurotransmission and excitotoxicity.

Glucose and glycogen are essential sources of energy for maintaining glutamate homeostasis as well as glutamatergic neurotransmission. The metabolism of glycogen, the location of which is confined to astrocytes, is affected by norepinephrine (NE), and hence, adrenergic signaling in the astrocyte might affect glutamate homeostasis with implications for excitatory neurotransmission and possibly excitotoxic neurodegeneration. In order to study this putative correlation, cultured astrocytes were incubated with 2.5 mM [U-(13)C]glucose in the presence and absence of NE as a time course for 1 h. Employing mass spectrometry, labeling in intracellular metabolites was determined. Moreover, the involvement of Ca(2+) in the noradrenergic response was studied. In unstimulated astrocytes, the labeling pattern of glutamate, aspartate, malate and citrate confirmed important roles for pyruvate carboxylation and oxidative decarboxylation in astrocytic glucose metabolism. Importantly, pyruvate carboxylation was best visualized at 10 min of incubation. The abundance and pattern of labeling in lactate and alanine indicated not only an extensive activity of malic enzyme (initial step for pyruvate recycling) but also a high degree of compartmentalization of the pyruvate pool. Stimulating with 1 µM NE had no effect on labeling patterns and glycogen metabolism, whereas 100 µM NE increased glutamate labeling and decreased labeling in alanine, the latter supposedly due to dilution from degradation of non-labeled glycogen. It is suggested that further experiments uncovering the correlation between adrenergic and glutamatergic pathways should be performed in order to gain further insight into the role of astrocytes in brain function and dysfunction, the latter including excitotoxicity.

Palladium-catalyzed decarboxylative rearrangements of allyl 2,2,2-trifluoroethyl malonates: direct access to homoallylic esters.

Homoallylic esters are obtained in a single transformation from allyl 2,2,2-trifluoroethyl malonates by using a Pd(0) catalyst. Facile decarboxylation of allyl 2,2,2-trifluoroethyl malonates is attributed to a decrease in pK(a) compared to allyl methyl malonates. Subsequent reduction of the homoallylic 2,2,2-trifluoroethyl ester provides a (hydroxyethyl)cyclopentenyl derivative that represents a key intermediate in the synthesis of carbocyclic nucleosides. A select allyl 2,2,2-trifluoroethyl malonate undergoes a decarboxylative Claisen rearrangement to provide a regioisomeric homoallylic ester.

Silver-catalysed protodecarboxylation of carboxylic acids.

A silver-based catalyst system has been discovered that effectively promotes the protodecarboxylation of various carboxylic acids at temperatures of 80-120 degrees C--more than 50 degrees C below those of the best known copper catalysts.