Total Synthesis of Luminmycin A, a Cryptic Natural Product from Photorhabdus Luminescens

Synthesis and biological evaluation of moiramide B derivatives

Moiramide B is a peptide-polyketide hybrid with a bacterial origin and interesting antibiotic activity. Besides its structurally conserved peptide part, it contains a highly variable fatty acid side chain. We modified this part of the molecule by introducing a terminal alkyne, and we then subjected it to click reactions and Sonogashira couplings. This provided a library of moiramide B derivatives with high and selective in vivo activities against S. aureus.

Synthesis and late stage modifications of Cyl derivatives

A peptide Claisen rearrangement is used as key step to generate a tetrapeptide with a C-terminal double unsaturated side chain. Activation and cyclization give direct access to cyclopeptides related to naturally occurring histone deacetylase (HDAC) inhibitors Cyl-1 and Cyl-2. Late stage modifications on the unsaturated amino acid side chain allow the introduction of functionalities which might coordinate to metal ions in the active center of metalloproteins, such as histone deacetylases.

Total synthesis of apratoxin A and B using Matteson's homologation approach

Apratoxin A and B, two members of an interesting class of marine cyclodepsipeptides are synthesized in a straightforward manner via Matteson homologation. Starting from a chiral boronic ester, the polyketide fragment of the apratoxins was obtained via five successive homologation steps in an overall yield of 27% and very good diastereoselectivity. This approach is highly flexible and should allow modification also of this part of the natural products, while previous modifications have been carried out mainly in the peptide fragment.

Activation, Structure, Biosynthesis and Bioactivity of Glidobactin-like Proteasome Inhibitors from Photorhabdus laumondii

The glidobactin-like natural products (GLNPs) glidobactin A and cepafungin I have been reported to be potent proteasome inhibitors and are regarded as promising candidates for anticancer drug development. Their biosynthetic gene cluster (BGC) plu1881-1877 is present in entomopathogenic Photorhabdus laumondii but silent under standard laboratory conditions. Here we show the largest subset of GLNPs, which are produced and identified after activation of the silent BGC in the native host and following heterologous expression of the BGC in Escherichia coli. Their chemical diversity results from a relaxed substrate specificity and flexible product release in the assembly line of GLNPs. Crystal structure analysis of the yeast proteasome in complex with new GLNPs suggests that the degree of unsaturation and the length of the aliphatic tail are critical for their bioactivity. The results in this study provide the basis to engineer the BGC for the generation of new GLNPs and to optimize these natural products resulting in potential drugs for cancer therapy.

Natural product scaffolds as inspiration for the design and synthesis of 20S human proteasome inhibitors

The 20S proteasome is a valuable target for the treatment of a number of diseases including cancer, neurodegenerative disease, and parasitic infection. In an effort to discover novel inhibitors of the 20S proteasome, many reseaarchers have looked to natural products as potential leads for drug discovery. The following review discusses the efforts made in the field to isolate and identify natural products as inhibitors of the proteasome. In addition, we describe some of the modifications made to natural products in order to discover more potent and selective inhibitors for potential disease treatment.