Daryamide Analogues from a Marine-Derived Streptomyces species

Natural epoxyquinoids: isolation, biological activity and synthesis. An update

Epoxyquinoids are of continuing interest due to their wide natural distribution and diverse biological activities, including, but not limited to, antibacterial, antifungal, anticancer, enzyme inhibitory, and others. The last review on their total synthesis was published in 2017. Since then, almost 100 articles have been published on their isolation from nature and their biological profile. In addition, the review specifically considers synthesis, including total and enantioselective, as well as the development of shorter approaches for the construction of epoxyquinoids with complex chemical architecture. Thus, this review focuses on progress in this area in order to stimulate further research.

Regioselective C(sp2)-H imidation of arenes by redox neutral visible-light photocatalysis

We report herein a redox neutral visible light-induced regioselective C(sp²)-H imidation of electron-rich arenes and heteroarenes using conceptually designed redox-active 1 as a source of the N-centered imidyl radical. Structurally diverse aromatic imides were obtained in moderate to good yields. This methodology has been successfully employed for the late stage imidation of complex molecules and has also been applied towards the formal total synthesis of the marine natural products carpatamides A, B and D. It has further been shown that the generated imides can easily be converted to the corresponding anilines in situ directly.

Streptomyces: The biofactory of secondary metabolites

Natural products derived from microorganisms serve as a vital resource of valuable pharmaceuticals and therapeutic agents. Streptomyces is the most ubiquitous bacterial genus in the environments with prolific capability to produce diverse and valuable natural products with significant biological activities in medicine, environments, food industries, and agronomy sectors. However, many natural products remain unexplored among Streptomyces. It is exigent to develop novel antibiotics, agrochemicals, anticancer medicines, etc., due to the fast growth in resistance to antibiotics, cancer chemotherapeutics, and pesticides. This review article focused the natural products secreted by Streptomyces and their function and importance in curing diseases and agriculture. Moreover, it discussed genomic-driven drug discovery strategies and also gave a future perspective for drug development from the Streptomyces.

Structure and Candidate Biosynthetic Gene Cluster of a Manumycin-Type Metabolite from Salinispora pacifica

A new manumycin-type natural product named pacificamide (1) and its candidate biosynthetic gene cluster (pac) were discovered from the marine actinobacterium Salinispora pacifica CNT-855. The structure of the compound was determined using NMR, electronic circular dichroism, and bioinformatic predictions. The pac gene cluster is unique to S. pacifica and found in only two of the 119 Salinispora genomes analyzed across nine species. Comparative analyses of biosynthetic gene clusters encoding the production of related manumycin-type compounds revealed genetic differences in accordance with the unique pacificamide structure. Further queries of manumycin-type gene clusters from public databases revealed their limited distribution across the phylum Actinobacteria and orphan diversity that suggests additional products remain to be discovered in this compound class. Production of the known metabolite triacsin D is also reported for the first time from the genus Salinispora. This study adds two classes of compounds to the natural product collective isolated from the genus Salinispora, which has proven to be a useful model for natural product research.

Marine natural products

Covering: January to December 2017This review covers the literature published in 2017 for marine natural products (MNPs), with 740 citations (723 for the period January to December 2017) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1490 in 477 papers for 2017), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. Geographic distributions of MNPs at a phylogenetic level are reported.

Nitrosopyridine Probe To Detect Polyketide Natural Products with Conjugated Alkenes: Discovery of Novodaryamide and Nocarditriene

An optimized nitroso-based probe that facilitates the discovery of conjugated alkene-containing natural products in unprocessed extracts was developed. It chemoselectively reacts with conjugated olefins via a nitroso-Diels-Alder cyclization to yield derivatives with a distinct chromophore and an isotopically unique bromine atom that can be rapidly identified using liquid chromatography/mass spectrometry and a bioinformatics tool called MeHaloCoA (Marine Halogenated Compound Analysis). The probe is ideally employed when genome-mining techniques identify strains containing polyketide gene clusters with two or more repeating KS-AT-DH-KR-ACP domain sequences, which are required for the biosynthesis of conjugated alkenes. Comparing the reactivity and spectral properties of five brominated arylnitroso reagents with model compounds spiramycin, bufalin, rapamycin, and rifampicin led to the identification of 5-bromo-2-nitrosopyridine as the most suitable probe structure. The utility of the dienophile probe was then demonstrated in bacterial extracts. Tylactone, novodaryamide and daryamide A, piperazimycin A, and the saccharamonopyrones A and B were cleanly labeled in extracts from their respective bacterial producers, in high regioselectivity but with varying degrees of diastereoselectivity. Further application of the method led to the discovery of a new natural product called nocarditriene, containing an unprecedented epoxy-2,3,4,5-tetrahydropyridine structure, from marine-derived Nocardiopsis strain CNY-503.

Carpatizine, a novel bridged oxazine derivative generated by non-enzymatic reactions

Carpatizine (1), a new bridged oxazine derivative, was isolated from a marine-derived Streptomyces strain SNE-011. The structure was fully determined by spectroscopic analysis, ECD calculations and chemical methods. A plausible non-enzymatic reaction mechanism from daryamide D leading to carpatizine was presented, which was confirmed by chemical transformation.