Mer-N5075A, a potential HIV-1 protease inhibitor, produced by Streptomyces chromofuscus

Genomes and secondary metabolomes of Streptomyces spp. isolated from Leontopodium nivale ssp. alpinum

Bacterial endophytes dwelling in medicinal plants represent an as yet underexplored source of bioactive natural products with the potential to be developed into drugs against various human diseases. For the first time, several Streptomyces spp. were isolated from the rare and endangered traditional medicinal plant Leontopodium nivale ssp. alpinum, also known as Edelweiss. In the search for novel natural products, nine endophytic Streptomyces spp. from Edelweiss were investigated via genome sequencing and analysis, followed by fermentation in different media and investigation of secondary metabolomes. A total of 214 secondary metabolite biosynthetic gene clusters (BGCs), of which 35 are presumably unique, were identified by the bioinformatics tool antiSMASH in the genomes of these isolates. LC-MS analyses of the secondary metabolomes of these isolates revealed their potential to produce both known and presumably novel secondary metabolites, whereby most of the identified molecules could be linked to their cognate BGCs. This work sets the stage for further investigation of endophytic streptomycetes from Edelweiss aimed at the discovery and characterization of novel bioactive natural products.

A practical total synthesis of the microbial alkaline proteinase inhibitor (MAPI)

Diverse serine and cysteine proteases as well as alkaline proteinases and elastases play a crucial role in numerous biological processes. Natural peptide aldehydes such as the "microbial alkaline proteinase inhibitor" (MAPI, 1) are valuable tools to characterize novel enzymes and to study their function in nature. Within a drug discovery program we wanted to design and explore non-natural MAPI congeners with novel biological profiles. To that end we devised a simple, practical, and scalable synthesis of MAPI 1 from readily available amino acid building blocks. The modular nature of our approach allows convenient structural modification of the MAPI backbone.

Preparation, isolation, and characterization of Nalpha-Fmoc-peptide isocyanates: solution synthesis of oligo-alpha-peptidyl ureas

The N(alpha)-Fmoc-peptide isocyanates 3a-q, 4a-c, and 5a-c were prepared by the Curtius rearrangement of N(alpha)-Fmoc-peptide acid azides in toluene under thermal, microwave, and ultrasonic conditions. All the N(alpha)-Fmoc-oligo-peptide isocyanates made were isolated as stable crystalline solids with 71 to 94% yield and were fully characterized by 1H NMR, 13C NMR, and mass spectroscopy. Their utility for the synthesis of oligo-alpha-peptidyl ureas 7a-f and 8a-c by the divergent coupling approach was demonstrated. The coupling of N(alpha)-Fmoc-dipeptide isocyanates with amino acid ester or with N,O-bis(trimethylsilyl)amino acids resulted in N(alpha)-Fmoc-tripeptidyl urea ester and acids containing one each of peptide bond and urea bond. The divergent approach is extended to the synthesis of tetrapeptidyl ureas by the 2 + 2 strategy using bis-TMS-peptide acid as an amino component. To incorporate urea bonds in adjacent positions, N(alpha)-Fmoc-peptidyl urea isocyanates 9a-d were prepared and employed in the synthesis of three tetrapeptidyl ureas 10a-b and 11 containing one peptide bond and two urea bonds in series from the N-terminal end. The protocol was then employed for the synthesis of five urea analogues 13-15, 18, and 21 of [Leu5]enkephalin containing urea bonds at the 2, 3, 4 positions as well as at the 2, 4 and 2, 3, 4 positions. The analogue 2l was made by the convergent synthesis by the N --> C terminal chain extension. Finally, two urea analogues 22 and 23 of repeat units of bioelasto polymers, namely Val-Pro-Gly-Val-Gly-OH and Pro-Gly-Val-Gly-Val-OH, were synthesized incorporating the urea bond by the concomitant isocyanate generation and urea bond formation under thermal conditions.

Hinnuliquinone, a C2-symmetric dimeric non-peptide fungal metabolite inhibitor of HIV-1 protease

HIV-1 protease is one of several key enzymes required for the replication and maturation of HIV-1 virus. An almost two-decade research effort by academic and pharmaceutical institutions resulted in the successful commercialization of seven drugs that are potent inhibitors of HIV-1 protease activity and which, if used correctly, are highly effective in managing viral load. However, identification of clinical viral isolates that are resistant to these drugs indicates that this is a significant problem and that new classes of inhibitors are continually needed. Screening of microbial extracts followed by bioassay-guided isolation led to the discovery of a natural hinnuliquinone, a C(2)-symmetric bis-indolyl quinone natural product that inhibited the wild-type and a clinically resistant (A44) strain of HIV-1 protease with K(i) values of 0.97 and 1.25microM, respectively. Crystallographic analysis of the inhibitor-bound HIV-1 protease helped explain the importance of the C(2)-symmetry of hinnuliquinone for activity. Details of the isolation, biological activity, and crystallographic analysis of the inhibitor-bound protease are herein described.

Recent examples of novel secondary metabolites

Modern trends in the detection, isolation and characterization of leads for novel therapeutic compounds are reviewed. Some current biological test systems (immunological, chemical, enzymic, receptor, etc.) and examples of their successful application are highlighted including the structures of selected novel and prospective metabolites.