Asymmetric Total Synthesis of Neoxaline

A first asymmetric total synthesis and determination of the absolute configuration of neoxaline has been accomplished through the highly stereoselective introduction of a reverse prenyl group to create a quaternary carbon stereocenter using (−)-3a-hydroxyfuroindoline as a building block, construction of the indoline spiroaminal via cautious stepwise oxidations with cyclizations from the indoline, assembly of (<i>Z</i>)-dehydrohistidine, and photoisomerization of unnatural (<i>Z</i>)-neoxaline to the natural (<i>E</i>)-neoxaline as the key steps

Actinoallolides A-E, new anti-trypanosomal macrolides, produced by an endophytic actinomycete, actinoallomurus fulvus MK10-036

d broth of Actinoallomurus fulvus MK10-036. The structures of the actinoallolides, including absolute stereochemistry, were elucidated by a combination of spectroscopic analyses and a series of chemical derivatization studies. Actinoallolide A showed the most potent and selective in vitro anti-trypanosomal activity without cytotoxicity. A new class of promising lead compounds was identified for the development of drugs for both sleeping sickness and Chagas disease

Total Synthesis and Determination of the Absolute Configuration of Naturally Occurring Mangromicin A, with Potent Antitrypanosomal Activity

An enantioselective total synthesis of (+)-mangromicin A has been accomplished. The tetrahydrofuran ring of mangromicin A, possessing a tetrasubstituted carbon center, was constructed by Mukaiyama-type vinylogous alkylation via a cyclic oxocarbenium intermediate derived from a γ-hydroxy ketone with ideal stereoselectivity, and the 4-hydroxydihydropyrone scaffold was generated via Dieckmann cyclization at a late stage of the total synthesis. The reliable asymmetric synthesis of (+)-mangromicin A has revealed the absolute configuration of naturally occurring mangromicin A

Molecular Insights into the Biosynthesis of Guadinomine: A Type III Secretion System Inhibitor

Guadinomines are a recently discovered family of anti-infective compounds produced by Streptomyces sp. K01-0509 with a novel mode of action. With an IC(50) of 14 nM, guadinomine B is the most potent known inhibitor of the type III secretion system (TTSS) of Gram-negative bacteria. TTSS activity is required for the virulence of many pathogenic Gram-negative bacteria including Escherichia coli , Salmonella spp., Yersinia spp., Chlamydia spp., Vibrio spp., and Pseudomonas spp. The guadinomine (gdn) biosynthetic gene cluster has been cloned and sequenced and includes 26 open reading frames spanning 51.2 kb. It encodes a chimeric multimodular polyketide synthase, a nonribosomal peptide synthetase, along with enzymes responsible for the biosynthesis of the unusual aminomalonyl-acyl carrier protein extender unit and the signature carbamoylated cyclic guanidine. Its identity was established by targeted disruption of the gene cluster as well as by heterologous expression and analysis of key enzymes in the biosynthetic pathway. Identifying the guadinomine gene cluster provides critical insight into the biosynthesis of these scarce but potentially important natural products

Isolation and Total Synthesis of Hoshinolactam, an Antitrypanosomal Lactam from a Marine Cyanobacterium

In the search for new antiprotozoal substances, hoshinolactam, an antitrypanosomal lactam, was isolated from a marine cyanobacterium. The gross structure was elucidated by spectroscopic analyses, and the absolute configuration was determined by the first total synthesis. Hoshinolactam showed potent antitrypanosomal activity with an IC₅₀ value of 3.9 nM without cytotoxicity against human fetal lung fibroblast MRC-5 cells (IC₅₀ > 25 μM)

Synthesis and Evaluation of Antibacterial Activity of Bottromycins

Total synthesis of bottromycin A₂ can be accomplished through a diastereoselective Mannich reaction of a chiral sulfinamide, mercury-mediated intermolecular amidination, and cyclization of a constrained tetracyclic peptide. Exploitation of this process allowed the synthesis of several novel bottromycin analogs. The antimicrobial activity of these analogs was evaluated in vitro against Gram-positive bacteria, such as methicillin resistant <i>Staphylococcus aureus</i> (MRSA) and vancomycin resistant <i>enterococci</i> (VRE). Structure–activity relationships were explored taking into consideration the unique three-dimensional structure of the compounds. Notably, one of the new analogs devoid of a methyl ester, which is known to lower the in vivo efficacy of bottromycin, exhibited antibacterial bioactivity comparable to that of vancomycin

Aogacillins A and B Produced by <i>Simplicillium</i> sp. FKI-5985: New Circumventors of Arbekacin Resistance in MRSA

Aogacillins A and B, capable of overcoming arbekacin resistance in methicillin-resistant <i>Staphylococcus aureus</i> (MRSA), were isolated from a culture broth of <i>Simplicillium</i> sp. FKI-5985. Their structures were elucidated by NMR spectroscopic studies and ECD analyses. The aogacillins possessed a novel carbon skeleton, including a β-keto-γ-methyliden-δ-lactone ring connected to a 2-ethyl-6-methylcyclohexane ring by spiro conjugation

Design and <i>De Novo</i> Synthesis of 6‑Aza-artemisinins

Development of designer natural product variants, 6-aza-artemisinins, enabled us to achieve structural modification of the hitherto unexplored cyclohexane moiety of artemisinin and concise <i>de novo</i> synthesis of the tetracyclic scaffold in just four steps from the modular assembly of three simple building blocks. This expeditious catalytic asymmetric synthetic approach generated lead candidates exhibiting superior <i>in vivo</i> antimalarial activities to artemisinin