Diphenylethanediamine (DPEDA) as chiral selector: VII. Efficient HPLC resolution of a series of underivatized diarylcarbinols on a chiral stationary phase based on C5-amide-bonded N-3,5-dinitrobenzoyl-DPEDA

Fast and efficient baseline separation of asymmetrically substituted diarylmethanols and 1,1-diarylethanols was achieved on an endcapped, amide-linked N-3,5-dinitrobenzoylated, (R, R)-1,2-diphenyl-1,2-ethanediamine-derived chiral stationary phase (CSP). Optimal enantioselectivities on this CSP were obtained using 1% 2-propanol in n-heptane as the mobile phase. Enantiorecognition was found to be governed by π-basicity and the substitution pattern of the aromatic substituents. © 1996 Wiley-Liss, Inc.     

The Life Histories of Two Temporarily Coexisting,Pond Dwelling Cladocerans

Investigations on the life histories of two cladocerans, Moina brachiata and Daphnia obtusa, in a small, nearly temporary pond in South Germany revealed that M. brachiata is better adapted to fluctuating environmental conditions; the species dominated from May to October. D. obtusa was present in spring and autumn/winter but disappeared completely during the summer months. Both species coexisted for extended periods in spring and autumn; abundance of D. obtusa was generally by an order of magnitute lower. Four periods of low water level were slightly preceded by or coincided with a decrease of clutch size, a decrease of the proportion of egg bearing females indicating that both species suffered from food shortage. Laboratory investigations on life history parameters showed that the two species have different temperature tolerances and preferences. M. brachiata showed its highest reproductive success at 25 and 30°C but died at temperatures <15°C and ≥ 35°C. D. obtusa experienced a broader temperature range (2 to 25°C) but could not withstand temperatures ≥ 30°C. Short term starvation periods (3d) caused the death of M. brachiata females, while D. obtusa soon recovered and reproduced when being refed. M. brachiata is a typical r-species with early reproduction, rapid development, high population growth rates and a high tendency to produce resting eggs; D. obtusa pursues more the concept of k-selection.     

Regulating peroxisome–ER contacts via the ACBD5-VAPB tether by FFAT motif phosphorylation and GSK3β

Peroxisomes and the endoplasmic reticulum (ER) cooperate in cellular lipid metabolism. They form membrane contacts through interaction of the peroxisomal membrane protein ACBD5 (acyl-coenzyme A–binding domain protein 5) and the ER-resident protein VAPB (vesicle-associated membrane protein–associated protein B). ACBD5 binds to the major sperm protein domain of VAPB via its FFAT-like (two phenylalanines [FF] in an acidic tract) motif. However, molecular mechanisms, which regulate formation of these membrane contact sites, are unknown. Here, we reveal that peroxisome–ER associations via the ACBD5-VAPB tether are regulated by phosphorylation. We show that ACBD5-VAPB binding is phosphatase-sensitive and identify phosphorylation sites in the flanking regions and core of the FFAT-like motif, which alter interaction with VAPB—and thus peroxisome–ER contact sites—differently. Moreover, we demonstrate that GSK3β (glycogen synthase kinase-3 β) regulates this interaction. Our findings reveal for the first time a molecular mechanism for the regulation of peroxisome–ER contacts in mammalian cells and expand the current model of FFAT motifs and VAP interaction.     

Chirality matters: stereo-defined phosphorothioate linkages at the termini of small interfering RNAs improve pharmacology in vivo

A critical challenge for the successful development of RNA interference-based therapeutics therapeutics has been the enhancement of their in vivo metabolic stability. In therapeutically relevant, fully chemically modified small interfering RNAs (siRNAs), modification of the two terminal phosphodiester linkages in each strand of the siRNA duplex with phosphorothioate (PS) is generally sufficient to protect against exonuclease degradation in vivo. Since PS linkages are chiral, we systematically studied the properties of siRNAs containing single chiral PS linkages at each strand terminus. We report an efficient and simple method to introduce chiral PS linkages and demonstrate that Rp diastereomers at the 5′ end and Sp diastereomers at the 3′ end of the antisense siRNA strand improved pharmacokinetic and pharmacodynamic properties in a mouse model. In silico modeling studies provide mechanistic insights into how the Rp isomer at the 5′ end and Sp isomer at the 3′ end of the antisense siRNA enhance Argonaute 2 (Ago2) loading and metabolic stability of siRNAs in a concerted manner.