HygY Is a Twitch Radical SAM Epimerase with Latent Dehydrogenase Activity Revealed upon Mutation of a Single Cysteine Residue.

HygY is a SPASM/twitch radical SAM enzyme hypothesized to catalyze the C2'-epimerization of galacamine during the biosynthesis of hygromycin B. This activity is confirmed via biochemical and structural analysis of the derivatized reaction products using chemically synthesized deuterated substrate, high-resolution mass spectrometry and 1H NMR. Electron paramagnetic resonance spectroscopy of the reduced enzyme is consistent with ligation of two [Fe4S4] clusters characteristic of the twitch radical SAM subgroup. HygY catalyzed epimerization proceeds with incorporation of a single solvent Hydron into the talamine product facilitated by the catalytic cysteine-183 residue. Mutation of this cysteine to alanine converts HygY from a C2'-epimerase to an C2'-dehydrogenase with comparable activity. The SPASM/twitch radical SAM enzymes often serve as anaerobic oxidases making the redox-neutral epimerases in this class rather interesting. The discovery of latent dehydrogenase activity in a twitch epimerase may therefore offer new insights into the mechanistic features that distinguish oxidative versus redox-neutral SPASM/twitch enzymes and lead to the evolution of new enzyme activities.

Dearomatization Reactions Using Phthaloyl Peroxide.

A new oxidative dearomatization reaction has been developed using phthaloyl peroxide to chemoselectively install two oxygen-carbon bonds into aromatic precursors. The oxidation reaction proceeds only once; addition of superstoichiometric equivalents of phthaloyl peroxide does not react further with the newly generated 1,3-cyclohexadiene. The reaction has been challenged by the addition of different functional groups and shown to maintain chemoselectivity. Due to the broad reactivity with 1,2-methylenedioxybenzene derivatives, linear free energy correlations were determined and support a mechanism proceeding through diradicals analogous to arene-hydroxylation reactions using phthaloyl peroxide.

Plasma is ineffective in correcting mildly elevated PT-INR in critically ill children: a retrospective observational study.

BACKGROUND: Fresh frozen plasma transfusion is widely utilized in pediatric clinical practice to correct mild coagulopathy. Several studies on adult population have shown that transfusion of plasma cannot effectively correct mild coagulopathy when international normalized ratio (INR) is ≤1.5. Much controversy exists about the generalization of this finding for pediatric populations, especially since pediatric dosages often exceed those in adults. The aim of this study is to determine the prevalence of plasma transfusion with mild coagulopathy (INR ≤ 1.5) and its effectiveness in a pediatric setting. METHODS: In our tertiary referral hospital, we retrospectively reviewed the electronic medical records of all patients who received plasma (April to October 2011) for mildly elevated prothrombin time (PT)-INR levels (≤1.5) and had post-transfusion PT-INR measurements; patients who received intraoperative, ECMO, or plasma exchange-related plasma transfusions were excluded from this study. We abstracted demographic data and pre- and post coagulation test results for the patients included in our study. RESULTS: Among 468 plasma transfusions administered to 285 patients from April to June 2011, 60 plasma transfusions (12.8%) were given to patients with PT-INR ≤ 1.5 (range 1.3-1.5). Forty-one patients [median age 2.5 years (IQR, 0.14 to 13.75 years), median weight of 16.0 kg (IQR, 8.0 to 69.3 kg)] who received 41 single plasma transfusions [median dose 11 mL/Kg (IQR, 6-15)] had post-transfusion PT-INR measurements and were included in our study. There was no significant difference in their PT-INR values (p = 0.34) pre- and post-transfusion. Of our study, only 15.4% patients showed post-transfusion normalization [median change in PT-INR 0.15 (IQR, 0.1-0.2)] and were not different from the remaining 85% in age, plasma dose, and bleeding status. CONCLUSIONS: The prevalence of plasma transfusion for correction of mildly elevated PT-INR levels in critically ill children is high (12.8%). Plasma transfusion showed no significant effect in correcting minor prolongation of PT-INR in pediatric patients regardless of age, volume of plasma transfused per kilogram (dosage), or bleeding status.

Indoles synthesized from amines via copper catalysis.

N-substituted indoles are synthesized from primary amines through a tandem reaction sequence. Initial condensation of the amine with an α-(o-haloaryl)ketone or aldehyde is followed by intramolecular aryl amination catalyzed by CuI. A variety of anilines and alkyl amines, including those with significant steric demands, are converted to indoles in high yields and with varying indole substitution.