Archazolid and apicularen: Novel specific V-ATPase inhibitors

Background  

V-ATPases constitute a ubiquitous family of heteromultimeric, proton translocating proteins. According to their localization in a multitude of eukaryotic membranes, they energize many different transport processes. Since their malfunction is correlated with various diseases in humans, the elucidation of the properties of this enzyme for the development of selective inhibitors and drugs is one of the challenges in V-ATPase research.     

Synthesis and biological evaluation of cruentaren A analogues

The complex macrolide cruentaren A is a highly selective and potent inhibitor of F-ATPase (F-type adenosine triphosphatase). As it shows some resemblance to benzolactone enamides like apicularen A, it was of interest to perform some structure-activity studies to delineate the key functional groups that are responsible for the activity. Building upon our previously developed route to cruentaren A, which is based on a ring-closing alkyne metathesis reaction (RCAM), several cruentaren analogues were prepared. Replacement of the 3-hydroxy hexanoic part with acids that lack the hydroxy group function resulted in a significant drop in cytotoxicity and F-ATPase inhibition. Furthermore, two enamide analogues 23 and 50 were synthesized. However, these compounds were only cytotoxic in the micromolar range. Under the conditions for cleavage of the C3 aromatic methyl ether, the enamide function was transformed to the corresponding oxazinanone, resulting in analogues 25 and 52.     

Development of erbium phosphate doped poly(glycidyl methacrylate/ethylene dimethacrylate) spin columns for selective enrichment of phosphopeptides

In this study, a novel method for the highly selective enrichment of phosphopeptides using erbium phosphate doped poly(glycidyl methacrylate/ethylene dimethacrylate) spin columns is presented. Erbium phosphate was synthesized by precipitation from boiling phosphoric acid and incubated overnight in erbium chloride solutions. The resulting powder was embedded in a monolithic poly(glycidyl methacrylate/ethylene dimethacrylate) polymer. The monolith was synthesized in a spin column by radical polymerization. Erbium phosphate demonstrated a high affinity and selectivity for phosphopeptides due to the strong interaction of trivalent erbium ions with the phosphate groups of phosphopeptides. The high selectivity and performance of the designed spin columns were demonstrated by successfully enriching phosphopeptides from tryptically digested protein mixtures containing the model phosphoproteins α‐ and β‐casein, bovine milk, and human saliva. By the implementation of several washing steps, unspecific components were removed and the enriched phosphopeptides were effectively eluted from the spin columns under alkaline conditions. The selective performance of the presented method was further demonstrated by the enrichment of two synthetic phosphopeptides, which were spiked in tryptically digested and dephosphorylated HeLa cell lysates at low ratios. Finally, the presented approach was compared to conventional phosphopeptide enrichment by titanium oxide and revealed higher recoveries for the erbium phosphate doped monoliths.     

An Improved Route to (+)‐Tedanolide and Analysis of Its Subtle Effects Controlling Conformation and Biological Behaviour

The improved synthesis of the antitumor compound (+)‐tedanolide is described through an aldol coupling of bis‐ketone 7 . This modification shortens the synthetic steps in the endgame and provides rapid access to this biologically important natural product. Additionally, it serves as a probe in order to unravel the conformational effects that impede or enable its successful synthesis. Having this way access to des‐epoxy‐tedanolide, its biological characterization surprisingly unravelled the mode of action to resemble candidaspongiolide rather than deoxytedanolide.     

On the Cycle Spectrum of Cubic Hamiltonian Graphs

We prove lower bounds on the number of different cycle lengths of cubic Hamiltonian graphs that do not contain a fixed subdivision of a claw as an induced subgraph.     

Broad substrate specificity of the amide synthase in S. hygroscopicus--new 20-membered macrolactones derived from geldanamycin

The amide synthase of the geldanamycin producer, Streptomyces hygroscopicus, shows a broader chemoselectivity than the corresponding amide synthase present in Actinosynnema pretiosum, the producer of the highly cytotoxic ansamycin antibiotics, the ansamitocins. This was demonstrated when blocked mutants of both strains incapable of biosynthesizing 3-amino-5-hydroxybenzoic acid (AHBA), the polyketide synthase starter unit of both natural products, were supplemented with 3-amino-5-hydroxymethylbenzoic acid instead. Unlike the ansamitocin producer A. pretiosum, S. hygroscopicus processed this modified starter unit not only to the expected 19-membered macrolactams but also to ring enlarged 20-membered macrolactones. The former mutaproducts revealed the sequence of transformations catalyzed by the post-PKS tailoring enzymes in geldanamycin biosynthesis. The unprecedented formation of the macrolactones together with molecular modeling studies shed light on the mode of action of the amide synthase responsible for macrocyclization. Obviously, the 3-hydroxymethyl substituent shows similar reactivity and accessibility toward C-1 of the seco-acid as the arylamino group, while phenolic hydroxyl groups lack this propensity to act as nucleophiles in the macrocyclization. The promiscuity of the amide synthase of S. hygroscopicus was further demonstrated by successful feeding of four other m-hydroxymethylbenzoic acids, leading to formation of the expected 20-membered macrocycles. Good to moderate antiproliferative activities were encountered for three of the five new geldanamycin derivatives, which matched well with a competition assay for Hsp90α.