Synthesis of 1,2-cis- and 1,2-trans-glycosides of 2-acetamido-4,6-O-benzylidene-2-deoxy-d-glucopyranose by anomeric O-alkylation

The reaction of a partially protected 1-hydroxy derivative of N-acetyl-d-glucosamine with benzyl bromide under conditions of anomeric O-alkylation was studied. It was found that the stereoselectivity of the reaction depended on the nature of the alkali metal cation constituent of a transient ion pair. The substitution of the Li⁺ cation for K⁺ or complexation with a crown ether allowed the steric outcome to be shifted from β- to α-selectivity.     

Ultrastructural patterns of photoacclimation and photodamage to photosynthetic algae cell under environmental stress

In oxygenic phototrophs including unicellular algae, acclimation to and damage by diverse environmental stresses induce profound changes in the ultrastructural organization of the cell. These alterations reflect acclimation of the photosynthetic apparatus to unfavorable conditions (mainly reduction of the chloroplast and its membranal system) and rewiring of the photo‐fixed carbon fluxes in the cell. These changes, eventually pursuing mitigation of the photooxidative damage risk, are manifested by the formation of diverse carbon‐rich inclusions. Although the physiological and molecular basis of these processes are well understood, the ultrastructural manifestations of the stress responses are often fragmented and frequently controversial. This minireview attempts to generalize on the ultrastructural patterns accompanying stresses in the photosynthetic cell, involving the concerted rearrangements of its assimilatory and storage compartments. The changes characteristic of normal functioning and emergency reduction of the chloroplast thylakoids under harsh stress are also addressed. Special attention is paid to the manifestations of the engagement of photoprotection via active (energy‐dependent non‐photochemical quenching) and passive mechanisms (e.g. optical shielding by secondary carotenoids). We also underline the potentially important role of autophagy‐like processes and provide a more integral view of ultrastructural rearrangements under stress.     

Intranasal insulin affects adenyl cyclase system in rat tissues in neonatal diabetes

The changes in hormone-regulated adenylyl cyclase (AC) signaling system implicated in control of the nervous, cardiovascular and reproductive systems may contribute to complications of diabetes mellitus (DM). We investigated the functional state of AC system in the brain, myocardium, ovary and uterus of rats with neonatal DM and examined the influence of intranasally administered insulin on the sensitivity of this system to biogenic amines and polypeptide hormones. The regulatory effects of somatostatin and 5-HT_1BR-agonist 5-nonyloxytryptamine acting via G_i protein-coupled receptors were significantly decreased in DM and partially restored in insulin-treated rats. The effects of hormones, activators of AC, are changed in tissue- and receptorspecific manner, and intranasal insulin restored the effects rather close to the level in control. In insulin-treated non-diabetic rats, AC stimulating effects of isoproterenol and relaxin in the myocardium and of human chorionic gonadotropin in the ovaries were decreased, while the effects of hormones, inhibitors of AC, were increased. These data indicate that with intranasal insulin, Gi protein-mediated signaling pathways continue to gain strength. The obtained data on the influence of hormones on AC system in the brain, myocardium, ovary and uterus allow looking anew into the mechanisms of therapeutic effects of intranasal insulin.     

Blood pressure and survival of a Chromosome 7 congenic strain bred from Dahl rats

11β-hydroxylase (Cyp11b1) mutations were previously linked to altered steroid biosynthesis and blood pressure in Dahl salt-resistant (R) and Dahl salt-sensitive (S) rats. In the present work, interval mapping identified a putative blood pressure quantitative trait locus (QTL) near Cyp11b1 in an F₁(S×R)×S population (LOD = 2.0). Congenic rats (designated S.R-Cyp11b) were constructed by introgressing the R-rat Cyp11b1 allele into the S strain. S.R-Cyp11b rats had significantly lower blood pressure and heart weight compared with S rats, proving the existence of a blood pressure QTL on Chromosome (Chr) 7 despite the fact that QTL linkage analysis of blood pressure never achieved stringent statistical criteria for significance. To test the effects of the introgressed region on blood pressure and survival, S.R.-Cyp11b and S rats were maintained on a 4% NaCl diet until they died or became moribund. Analysis of variance (ANOVA) indicated significant strain differences in blood pressure and days survived (P < 0.0001 for both) as well as gender differences in days survived (P = 0.0003). Kaplan-Meier survival analysis also found significant strain (P < 0.0001) and gender (P = 0.007) differences in days survived. However, when the effects of blood pressure were removed, significant strain differences in survival essentially disappeared. This suggests that the increased survival of S.R-Cyp11b rats was largely due to their decreased blood pressure and thus strongly corroborates the existence of a blood pressure QTL on Chr 7 near or at Cyp11b1. Received: 7 April 1997 / Accepted: 10 August 1997