Co-produced natural ketolides methymycin and pikromycin inhibit bacterial growth by preventing synthesis of a limited number of proteins.

Antibiotics methymycin (MTM) and pikromycin (PKM), co-produced by Streptomyces venezuelae, represent minimalist macrolide protein synthesis inhibitors. Unlike other macrolides, which carry several side chains, a single desosamine sugar is attached to the macrolactone ring of MTM and PKM. In addition, the macrolactone scaffold of MTM is smaller than in other macrolides.

Synthesis of (-)-oseltamivir phosphate (Tamiflu) starting from cis-2,3-bis(hydroxymethyl)aziridine.

Oseltamivir phosphate (Tamiflu) has been synthesized from cis-2,3-bis(hydroxymethyl)aziridine. After protection of the cis-2,3-bis(hydroxymethyl)aziridine with a Boc group, desymmetrization provided a chiral aziridine, which was a key intermediate to install the required stereogenic center containing a nitrogen atom. Allylation and ring closing metathesis are the key reactions to obtain the cyclic product that was successfully converted to the desired oseltamivir phosphate.

Total synthesis of pikromycin.

The total synthesis of pikromycin (6), the first isolated macrolide antibiotic, was achieved. The target macrolide was retrosynthetically divided into two parts, pikronolide (6a) (aglycon) and D-desosamine. The aglycon was synthesized using key reactions such as an asymmetric aldol reaction, Yamaguchi esterification, and ring-closing metathesis.

Total synthesis of methymycin.

Methynolide and 10-epi-methynolide were synthesized from the necessary segments, which were prepared by the addition of Grignard reagents to the corresponding alpha-alkoxyketones utilizing 1,2-stereochemical selection based on Cram chelation control. Ring-closing metathesis, as the key reaction, was carried out to combine the segments for the synthesis of methynolide and 10-epi-methynolide. The total synthesis of methymycin was also achieved by the glycosylation of methynolide with the trichloroimidate derivative of D-desosamine.

Exploiting the natural metabolic diversity of Streptomyces venezuelae to generate unusual reduced macrolides.

An unusual set of reduced macrolide antibiotics was discovered by combination of organic synthesis and a biosynthetic approach using the unique metabolic diversity of Streptomyces venezuelae; two unnatural 16-membered ring macrolides are also created by employing this bio-catalyst.

Synthesis of chroman-2-carboxylic acid N-(substituted)phenylamides and their inhibitory effect on nuclear factor-kappaB (NF-kappaB) activation.

A series of chroman-2-carboxylic acid N-(substituted)phenylamides (2a-s, 3a-j) were synthesized. Their ability to inhibit nuclear factor-kappaB (NF-kappaB) activity was evaluated in lipopolysaccharide (LPS)-stimulated macrophage RAW 264.7 cells and their antioxidant activity was examined.

Total synthesis of 10-deoxymethynolide and narbonolide.

A flexible and convenient approach was developed for the synthesis of 10-deoxymethynolide (1) and narbonolide (2), which are aglycones of the methymycin and the pikromycin families of macrolide antibiotics. These lactones are produced by pikromycin polyketide synthase from Streptomyces venezuelae. Polyketide lactones, 10-deoxymethynolide and narbonolide, which contain 12- and 14-membered rings, respectively, were synthesized efficiently.

Coupled expression of MhpE aldolase and MhpF dehydrogenase in Escherichia coli.

MhpE (4-hydroxy-2-ketovalerate aldolase) and MhpF [acetaldehyde dehydrogenase (acylating)] are responsible for the last two reactions in the 3-(3-hydroxyphenyl)propionate (3-HPP) catabolic pathway in Escherichia coli, which is homologous to the meta-cleavage pathway in Pseudomonas species. Here, we report that the MhpE aldolase is associated with the MhpF dehydrogenase and that MhpF is indispensable for the folding of MhpE. Moreover, our results suggest that the mhpF and mhpE genes are translationally coupled through a reinitiation mechanism.

Generation of multiple bioactive macrolides by hybrid modular polyketide synthases in Streptomyces venezuelae.

The plasmid-based replacement of the multifunctional protein subunits of the pikromycin PKS in S. venezuelae by the corresponding subunits from heterologous modular PKSs resulted in recombinant strains that produce both 12- and 14-membered ring macrolactones with predicted structural alterations. In all cases, novel macrolactones were produced and further modified by the DesVII glycosyltransferase and PikC hydroxylase, leading to biologically active macrolide structures.