Synthesis of N- and side chain protected aspartyl and glutamyl aldehyde derivatives. Reinvestigation of the reduction of Weinreb amides

Transition Metal-Mediated Annulation Approaches for Synthesis of Arylnaphthalene Lignan Lactones

Arylnaphthalene lignan lactones belong to a class of natural lignans, and more than 60 analogs have been isolated. Their pharmacological activities as well as unique structural features have attracted considerable attention from medicinal and synthetic chemists. Since the first synthesis in 1895, many synthetic methodologies with ionic or pericyclic reaction mechanisms have been reported. Transition metal catalysts sometimes provide exceptional synthetic versatility for the syntheses of natural compounds. Recently, transition metal-mediated methodologies were investigated for the construction of basic scaffolds of arylnaphthalene lignan lactones. Five kinds of transition metal catalysts containing gold, manganese, nickel, palladium, and silver have been explored. Most of the metal catalysts successfully created arylnaphthalene lactones by intermolecular or intramolecular annulative cyclization. In this review, all reports of transition metal-mediated annulative construction of arylnaphthalene lignan lactones were compiled, and synthetic approaches, mechanistic aspects, and successful applications were discussed.

How do haloarchaea synthesize aromatic amino acids?

Genomic analysis of H. salinarum indicated that the de novo pathway for aromatic amino acid (AroAA) biosynthesis does not follow the classical pathway but begins from non-classical precursors, as is the case for M. jannaschii. The first two steps in the pathway were predicted to be carried out by genes OE1472F and OE1475F, while the 3^rd step follows the canonical pathway involving gene OE1477R. The functions of these genes and their products were tested by biochemical and genetic methods. In this study, we provide evidence that supports the role of proteins OE1472F and OE1475F catalyzing consecutive enzymatic reactions leading to the production of 3-dehydroquinate (DHQ), after which AroAA production proceeds via the canonical pathway starting with the formation of DHS (dehydroshikimate), catalyzed by the product of ORF OE1477R. Nutritional requirements and AroAA uptake studies of the mutants gave results that were consistent with the proposed roles of these ORFs in AroAA biosynthesis. DNA microarray data indicated that the 13 genes of the canonical pathway appear to be utilised for AroAA biosynthesis in H. salinarum, as they are differentially expressed when cells are grown in medium lacking AroAA.

Progress in the preparation of peptide aldehydes via polymer supported IBX oxidation and scavenging by threonyl resin

Peptide aldehydes are of interest due to their inhibitory properties toward numerous classes of proteolytic enzymes such as caspases or the proteasome. A novel access to peptide aldehydes is described using a combination of solid phase peptide synthesis with polymer-assisted solution phase synthesis based on the oxidation of peptide alcohols with a mild and selective polymer-bound IBX derivative. The oxidation is followed by selective purification via scavenging the peptide aldehyde in a capture-release procedure using threonine attached to an aminomethyl resin. Peptide aldehydes are obtained in excellent purity and satisfying yield. The optical integrity of the C-terminal residue is conserved in a high degree. The procedures are compatible with the use of common side-chain protecting groups. The potential for using the method in parallel approaches is very advantageous. A small collection of new and known peptide aldehydes has been tested for inhibitory activity against caspases 1 and 3.

Peptidomimetic glutathione analogues as novel gammaGT stable GST inhibitors

Elevated levels of glutathione-S-transferase (GST) isoenzymes are found in many tumor cells and are thought to play a role in the onset of multidrug resistance (MDR). To evaluate the contribution of GST to this process, inhibitors are needed. Glutathione (GSH) conjugates, although good GST inhibitors, cannot be used in vivo, because they are eliminated rapidly. In this paper, we describe the synthesis of a series of novel peptidomimetic glutathione analogues that are stabilized against peptidase mediated breakdown. The peptide bonds in GSH were replaced by isosteres, such as the 'reduced' amide (which was prepared using a novel method), N-methylamide, urethane, and methylene linkages. The in vitro evaluation of the compounds focuses on GST inhibition and stability towards gamma-glutamyl-transpeptidase (gammaGT), the main enzyme involved in GSH breakdown. The compounds were conjugated to the model electrophile ethacrynic acid (EA) to resemble GS-EA, an efficient GST inhibitor. All novel GSH-analogues were shown to inhibit rat liver cytosolic GSTs. Furthermore, peptidomimetic changes of the gamma-glutamyl-cysteine amide bond greatly improved stability towards gammaGT. These compounds may therefore be useful in the design of novel in vivo applicable GST inhibitors.

A new amino acid derivative with a masked side-chain aldehyde and its use in peptide synthesis and chemoselective ligation

A new amino acid derivative with a diol side-chain, L-2-amino-4,5-dihydroxy-pentanoic acid (Adi), has been prepared from L-allylglycine by suitable protection, for use in peptide synthesis, as Fmoc-L-Adi(Trt)2. This building block enables the introduction of a side-chain aldehyde at any position in a given peptide sequence without use of specialized side-chain protection schemes. The aldehyde is revealed by mild oxidation with sodium periodate, circumventing the problematic release of reactive peptidic aldehydes in TFA solution. Peptides with aldehyde side-chains are useful for chemo-selective ligation, reacting selectively with oxyamines to yield oxime links, while all other peptide functions can be left unprotected. The utility of the new building block has been demonstrated by the synthesis of peptide dimers and a cyclo-peptide.