Electrophilic reactivities of cyclic enones and α,ß-unsaturated lactones.

The reactivities of cyclic enones and α,ß-unsaturated lactones were characterized by following the kinetics of their reactions with colored carbon-centered reference nucleophiles in DMSO at 20 °C. The experimentally determined second-order rate constants k 2 were analyzed with the Mayr-Patz equation, lg k = s N(N + E), to furnish the electrophilicity descriptors E for the Michael acceptors. Cyclic enones and lactones show different reactivity trends than their acyclic analogs. While cyclization reduces the reactivity of enones slightly, α,ß-unsaturated lactones are significantly more reactive Michael acceptors than analogously substituted open-chain esters. The observed reactivity trends were rationalized through quantum-chemically calculated Gibbs energy profiles (at the SMD(DMSO)/M06-2X/6-31+G(d,p) level of theory) and distortion interaction analysis for the reactions of the cyclic Michael acceptors with a sulfonium ylide. The electrophilicities of simplified electrophilic fragments reflect the general reactivity pattern of structurally more complex terpene-derived cyclic enones and sesquiterpene lactones, such as parthenolide.

A tailored phosphoaspartate probe unravels CprR as a response regulator in Pseudomonas aeruginosa interkingdom signaling.

Pseudomonas aeruginosa is a difficult-to-treat Gram-negative bacterial pathogen causing life-threatening infections. Adaptive resistance (AR) to cationic peptide antibiotics such as polymyxin B impairs the therapeutic success. This self-protection is mediated by two component systems (TCSs) consisting of a membrane-bound histidine kinase and an intracellular response regulator (RR). As phosphorylation of the key RR aspartate residue is transient during signaling and hydrolytically unstable, the study of these systems is challenging. Here, we apply a tailored reverse polarity chemical proteomic strategy to capture this transient modification and read-out RR phosphorylation in complex proteomes using a nucleophilic probe. In-depth mechanistic insights into an ideal trapping strategy were performed with a recombinant RR demonstrating the importance of fine-tuned acidic pH values to facilitate the attack on the aspartate carbonyl C-atom and prevent unproductive hydrolysis. Analysis of Bacillus subtilis and P. aeruginosa proteomes revealed the detection of multiple annotated phosphoaspartate (pAsp) sites of known RRs in addition to many new potential pAsp sites. With this validated strategy we dissected the signaling of dynorphin A, a human peptide stress hormone, which is sensed by P. aeruginosa to prepare AR. Intriguingly, our methodology identified CprR as an unprecedented RR in dynorphin A interkingdom signaling.

Effect of diet on infant subcutaneous tissue triglyceride fatty acids.

Having demonstrated a deficiency in infant cerebral cortex docosahexaenoic acid of formula fed compared with breast milk fed infants, we sought to identify why the extensive subcutaneous tissue triglyceride fatty acid reserves in term new-born infants appeared to be ineffectual in its prevention. In addition to 24 term and six preterm infants who died from 'cot death', tissue was analysed from four perinatal surgical patients and in the former the results were correlated with dietary milk intake. The higher amounts (about 15% by weight) of unsaturated linoleic acid supplied in the formula milks were quantitatively incorporated into the subcutaneous tissue largely at the expense of the saturated palmitic acid possibly compromising adipocyte fluidity. The six preterm infants were in two formula fed groups and there was only one significant difference, namely a higher subcutaneous tissue concentration of alpha-linolenic acid in one of the preterm groups, distinguishing them from their term counterparts. This may imply that the enzymes involved in absorption and digestion of fatty acids are mature in the preterm infant. From birth the mean weight percentage of docosahexaenoic acid (0.4%) fell rapidly to undetectable levels (< 0.05%) in the formula fed group after about two months. It is therefore concluded that if breast feeding is not possible then a minimum daily requirement of 30 mg docosahexaenoic acid (approximately 0.2 g/100 g fatty acids) should be supplied in formulas designed for term infants to prevent the cerebral cortical deficiency of docosahexaenoic acid.

Infant cerebral cortex phospholipid fatty-acid composition and diet.

It has not been established whether nutrition in early infancy affects subsequent neurodevelopment and function. If there is an effect, it seems probable that the essential fatty acids and their metabolites, the major constituents of brain structure, will be the most susceptible to dietary influence. We determined the phospholipid fatty-acid composition of cerebral cortex grey matter obtained from 20 term and 2 preterm infants who had died of "cot deaths" and related results to the milk diet the infants had received. Tissues were analysed by gas chromatography. The mean weight percentage of docosahexaenoic acid was significantly greater (p less than 0.02) in 5 breast-milk-fed infants (9.7%) than in 5 age-comparable formula-milk-fed infants (7.6%). In these formula-fed babies, the overall percentage of long-chain polyunsaturated fatty acids was maintained by increased incorporation of the major n-6 series fatty acids. In 1 formula-fed preterm infant, in whom the lowest concentration of cortical docosahexaenoic acid was found, the compensatory effect was only partial with both n-9 series eicosatrienoic acid or Mead acid and docosatrienoic acid also detected in the phospholipid. Supplementation of formula milks for term infants with docosahexaenoic acid and those for preterm infants with both docosahexaenoic and arachidonic acid could prove beneficial to subsequent neurodevelopment.