Serine racemase (SR) is a brain enzyme present in glial cells, where it isomerizes L-serine into D-serine that, in turn, diffuses and coactivates the N-methyl-D-aspartate receptor through the binding to the so-called "glycine site." We have developed a method for the slow expression of SR in a eukaryotic vector that permits the correct insertion of the prosthetic group into the active site, rendering functional SR with a K m toward L-serine of 4.8 mM. Divalent cations such as calcium or manganese were necessary for complete enzyme activity, whereas the presence of chelators such as EDTA completely inhibited the enzyme. Moreover, direct binding of calcium to SR was evidenced using 45 Ca 2؉ . Gel filtration of the recombinant SR revealed the protein to be in a dimer-tetramer equilibrium. The addition of EDTA to a calcium-saturated serine racemase evokes a profound conformational change, as monitored by both fluorescence and circular dichroism techniques. Fluorescence titration allowed us to calculate a binding constant for calcium of 6.2 M. Reagents that react with sulfhydryl groups, such as cystamine, were potent inhibitors of SR, in a clear reflection that one or more cysteine residues are important for enzyme activity. Additionally, 16 serine analogues were tested as a putative SR substrate or inhibitors. Significant inhibition was only observed for L-Ser-O-sulfate, L-cycloserine, and L-cysteine. Finally, activation of brain SR as a result of the changes in calcium concentration was studied in primary astrocytes. Treatment of astrocytes with the calcium ionophore A23187, as well as with compounds that augment the intracellular calcium levels such as glutamate or kainate led to an increase in the amount of D-serine present in the extracellular medium. These results suggest that there might be a glutamatergic-mediated regulation of SR activity by intracellular calcium concentration.D-Amino acids have been known for decades to be present in bacteria, where they are important constituents of peptidoglycan in the cell wall. Interestingly, recent improvement in the detection techniques has allowed the identification of significant levels of both D-serine (1-3) and D-aspartic acid (3, 4) in the nervous system of vertebrates. Snyder and co-workers (5, 6) have elegantly purified and subsequently cloned the cDNA for a novel enzyme responsible for the synthesis of D-serine in the brain and identified it as a 37-kDa pyridoxal phosphate-containing racemase present in astrocytes. These protoplasmic astrocytes typically ensheath synapses, strongly suggesting a role for D-serine in synaptic transmission. Serine racemase is highly enriched in the brain and co-localizes with D-serine according to immunohistochemical analysis (6). Additionally, D-serine is concentrated in regions enriched in N-methyl-Daspartate (NMDA) 1 receptors (i.e. highest in the forebrain), whereas the levels of the previously identified NMDA receptor coactivator, glycine, are lowest in this region (7,8). Remarkably, recent reports have also identified D-ser...

This communication describes a mild, amide-directed fluorination of benzylic, allylic, and unactivated C-H bonds mediated by iron. Upon exposure to a catalytic amount of iron(II) triflate (Fe(OTf)), N-fluoro-2-methylbenzamides undergo chemoselective fluorine transfer to provide the corresponding fluorides in high yield. The reaction demonstrates broad substrate scope and functional group tolerance without the use of any noble metal additives. Mechanistic and computational experiments suggest that the reaction proceeds through short-lived radical intermediates with F-transfer mediated directly by iron.

Malaria represents one of the most medically and economically debilitating diseases present in the world today. Fortunately, there exists a highly effective treatment based on the natural product artemisinin. Despite the development of several synthetic approaches to the natural product, a streamlined synthesis that utilizes low-cost chemical inputs has yet to materialize. Here we report an efficient, cost-effective approach to artemisinin. Key to the success of the strategy was the development of mild, complexity-building reaction cascades that allowed the use of readily available, affordable cyclohexenone as the key starting material.

The use of low-cost iron(III) acetoacetate (Fe(acac)3) and tetramethylethylenediamine (TMEDA) enables the direct cross-coupling of alkyl halides with bis(pinacolato)diboron. This approach allows for the borylation of activated or unactivated primary, secondary, and tertiary bromides. Moreover, even the borylation of benzylic or allylic chlorides, tosylates, and mesylates are possible. The reactions proceed under mild conditions at room temperature and show broad functional-group compatibility and "robustness" as measured by a modified Glorius robustness screen.

The use of low-cost manganese­(II) bromide (MnBr2) and tetramethyl­ethylene­diamine (TMEDA) catalyzes the cross coupling of (bis)­pinacolato­diboron with a wide range of alkyl halides, demonstrating the first manganese-catalyzed coupling with alkyl electrophiles. This method allows access to primary, secondary, and tertiary boronic esters from the parent chlorides, which were previously inaccessible as coupling partners. The reaction proceeds in high yield with as little as 1000 ppm catalyst loading, while 5 mol % can provide high yields in as little as 30 min. Finally, radical-clock experiments revealed that at 0 °C direct borylation outcompetes alternative radical processes, thereby providing synthetically useful, temperature-controlled reaction outcomes.