Synthesis of the Anomers of Hepta‐ O ‐acetylcellobiosyl, ‐lactosyl, ‐maltosyl, and ‐melibiosyl Azide Synthesis and characterization by 13 C‐NMR spectroscopy of the O ‐acetylated 1,2‐ cis and 1,2‐ trans azides of cellobiose, lactose, maltose, and melibiose have been accomplished. 1,2‐ trans Azides 1c , 2b–4b result from the stannic chloride catalyzed reaction of the β‐octa‐ O ‐acetates 1a–4a with trimethylsilyl azide, whereas the β‐chlorohepta‐ O ‐acetyldisaccharides 1d, 2c–4c afford, in an S N 2 reaction in HMPT with lithium azide, the hitherto inaccessible 1,2‐ cis azides 1e, 2d–4d .
The titration of 13C labeled N-acetyl-D-ala-D-ala with the glycopeptide antibiotics ristocetin A and eremomycin, monitored by 13C NMR spectroscopy, demonstrates that the two distinct binding sites of the ristocetin A asymmetric dimer have different affinities, whereas those of eremomycin show no detectable difference.
Azidolysis of C-19 diastereoisomer tosylesters of morphine derivatives possessing a bridged ring C has been studied and 4-azatetracyclo[4.4.02,4.03,8]decanes 6b, 6d and 6f were formed via the substitution and subsequent intramolecular cyclization of the (R)-C-19 tosylesters 4b, 4d and 4f, and primarily the ethylidene derivatives 7a, 7b and 7c were obtained from (S)-C-19 tosylesters 4c, 4e and 4g. According to our experience the course of the reaction depends on the configuration of the C-19 centre of chirality and on the spatial requirement of the substitutent on C-6
The formation of supramolecular polymeric aggregates with a molecular mass of 100 kDa in a nonaqueous solution from a telechelic dimer of isopropylidene guanosine in the presence of K+ ions is reported. The possible structure of macromonomers resulting from the development of G4 quartets was deduced from DOSY NMR, circular dichroism spectra, and dynamic light scattering measurements.
P-glycoprotein (Pgp, ABCB1) is a member of one of the largest families of active transporter proteins called ABC transporters. Thanks to its expression in tissues with barrier functions and its broad substrate spectrum, it is an important determinant of the absorption, metabolism and excretion of many drugs. Pgp and/or some other drug transporting ABC proteins (e.g., ABCG2, MRP1) are overexpressed in nearly all cancers and cancer stem cells by which cancer cells become resistant against many drugs. Thus, Pgp inhibition might be a strategy for fighting against drug-resistant cancer cells. Previous studies have shown that certain polyphenols interact with human Pgp. We tested the effect of 15 polyphenols of sour cherry origin on the basal and verapamil-stimulated ATPase activity of Pgp, calcein-AM and daunorubicin transport as well as on the conformation of Pgp using the conformation sensitive UIC2 mAb. We found that quercetin, quercetin-3-glucoside, narcissoside and ellagic acid inhibited the ATPase activity of Pgp and increased the accumulation of calcein and daunorubicin by Pgp-positive cells. Cyanidin-3O-sophoroside, catechin, naringenin, kuromanin and caffeic acid increased the ATPase activity of Pgp, while they had only a weaker effect on the intracellular accumulation of fluorescent Pgp substrates. Several tested polyphenols including epicatechin, trans-ferulic acid, oenin, malvin and chlorogenic acid were ineffective in all assays applied. Interestingly, catechin and epicatechin behave differently, although they are stereoisomers. We also investigated the effect of quercetin, naringenin and ellagic acid added in combination with verapamil on the transport activity of Pgp. In these experiments, we found that the transport inhibitory effect of the tested polyphenols and verapamil was additive or synergistic. Generally, our data demonstrate diverse interactions of the tested polyphenols with Pgp. Our results also call attention to the potential risks of drug-drug interactions (DDIs) associated with the consumption of dietary polyphenols concurrently with chemotherapy treatment involving Pgp substrate/inhibitor drugs.
alpha-CD was converted into hexakis[2,6-di-O-(methoxydimethyl)methyl]-alpha-CD by a proton-catalyzed reaction with 2-methoxypropene. Subsequent benzylation under Brimacombe conditions resulted in the fully protected compound, from which the acid-sensitive acetal groups were removed to obtain hexakis(3-O-benzyl)-alpha-cyclodextrin. The structure of all of the compounds synthesized was confirmed by 13C J-ECHO, COSY, HETCOR and HMBC NMR measurements.
Fungal pathogens, from phytopathogenic fungus to human pathogens, are able to alternate between the yeast-like form and filamentous forms. This morphological transition (dimorphism) is in close connection with their pathogenic lifestyles and with their responses to changing environmental conditions. The mechanisms governing these morphogenetic conversions are still not fully understood. Therefore, we studied the filamentous growth of the less-known, non-pathogenic dimorphic fission yeast, S. japonicus, which belongs to an ancient and early evolved branch of the Ascomycota. Its RNA sequencing revealed that several hundred genes were up- or down-regulated in the hyphae compared to the yeast-phase cells. These genes belonged to different GO categories, confirming that mycelial growth is a rather complex process. The genes of transport- and metabolic processes appeared especially in high numbers among them. High expression of genes involved in glycolysis and ethanol production was found in the hyphae, while other results pointed to the regulatory role of the protein kinase A (PKA) pathway. The homologues of 49 S. japonicus filament-associated genes were found by sequence alignments also in seven distantly related dimorphic and filamentous species. The comparative genomic analyses between S. japonicus and the closely related but non-dimorphic S. pombe shed some light on the differences in their genomes. All these data can contribute to a better understanding of hyphal growth and those genomic rearrangements that underlie it.
