Singlet molecular oxygen ( 1 O 2 ) has well-established roles in photosynthetic plants, bacteria and fungi 1-3 , but not in mammals. Chemically generated 1 O 2 oxidizes the amino acid tryptophan to precursors of a key metabolite called N-formylkynurenine 4 , while enzymatic oxidation of tryptophan to N-formylkynurenine is catalyzed by a family of dioxygenases, including indoleamine 2,3-dioxygenase 1 5 . Under inflammatory conditions, this hemecontaining enzyme becomes expressed in arterial endothelial cells, where it contributes to the regulation of blood pressure 6 . However, whether indoleamine 2,3-dioxygenase 1 forms 1 O 2 and whether this contributes to blood pressure control is unknown. Here we show that arterial indoleamine 2,3-dioxygenase 1 regulates blood pressure via formation of 1 O 2 . We observed that in the presence of hydrogen peroxide, the enzyme generates 1 O 2 and that this is associated with the stereoselective oxidation of L-tryptophan to a tricyclic hydroperoxide via a previously unrecognized oxidative activation of the dioxygenase activity. The tryptophanderived hydroperoxide acts as a hitherto undiscovered signaling molecule in vivo, which induces arterial relaxation and decreases blood pressure dependent on cysteine residue 42 of protein kinase G1α. Our findings demonstrate a pathophysiological role for 1 O 2 in mammals through formation of an amino acid-derived hydroperoxide that regulates vascular tone and blood pressure under inflammatory conditions. Several small molecules, such as nitric oxide and hydrogen peroxide (H 2 O 2 ) regulate cellular signaling via interaction with proteins containing redox active metals and/or cysteine residues. Of these molecules, nitric oxide, formed from L-arginine by endothelial nitric oxide synthase, is an important regulator of vascular tone 7 . Sustained increases in nitric oxide synthesis by inducible nitric oxide synthase, as observed in pathological settings such as sepsis, are associated with profound hypotension 8 . Paradoxically, inhibitors of the nitric oxide pathway have generally failed to ameliorate severe septic shock 9,10 , suggesting involvement of additional mediators of hypotension.Based on functional similarity with the metabolism of L-arginine by nitric oxide synthase, we 3 reported previously that metabolism of L-tryptophan (Trp) to N-formylkynurenine (NFK) and kynurenine by endothelial indoleamine 2,3-dioxygenase 1 (IDO1) ( Fig. 1a) contributes to the regulation of vascular tone and blood pressure in inflammation 6 . We also showed that commercial kynurenine relaxed pre-constricted arteries, which suggested that kynurenine is an endotheliumderived relaxant factor 6 . Although others have since confirmed these findings 11,12 , we noticed that recently purchased kynurenine no longer caused arterial relaxation, and that HPLC-purified kynurenine and NFK also failed to relax naïve mouse arteries ( Fig. 1b). However, purified Trp relaxed pre-constricted mouse abdominal aortas that expressed IDO1, irrespective of whether IDO1 expression was...

A total synthesis of ageladine A has been achieved by exploiting a Pictet-Spengler-type condensation between 2-aminohistamine and 4,5-dibromo-2-formylpyrrole as the key step.

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Background: Myeloperoxidase activity is commonly assessed in vivo by the accumulation of 3-chlorotyrosine. Results: Myeloperoxidase-derived chlorinating species specifically converted hydroethidine to 2-chloroethidium with efficiency superior to that of the corresponding conversion of tyrosine to 3-chlorotyrosine. Conclusion: Hydroethidine is useful to assess myeloperoxidase activity in vivo, in parallel with its simultaneous use to detect superoxide. Significance: 2-Chloroethidium is a useful additional marker of myeloperoxidase activity.

A one-pot synthesis of ageladine A and analogues is reported. The key Pictet-Spengler reaction between 2-aminohistamine and aryl aldehydes has been successfully utilized for the synthesis of the natural product and 14 analogues. These compounds were screened for their matrix metalloprotease (MMP) and kinase inhibition to develop the first structure-activity relationship of ageladine A analogues. One compound, which showed significant kinase activity but little MMP inhibitory activity, was found to be highly active in an antiangiogenic screen, suggesting that the angiogenic activity of ageladine A is not associated with MMP inhibition but rather kinase inhibitory activity. Cytotoxicity was excluded as a mode of action by the assay of ageladine A and an analogue against 60 human cell lines.