Rapid and Systematic Exploration of Chemical Space Relevant to Artemisinins: Anti-malarial Activities of Skeletally Diversified Tetracyclic Peroxides and 6-Aza-artemisinins.

To achieve both structural changes and rapid synthesis of the tetracyclic scaffold relevant to artemisinins, we explored two kinds of de novo synthetic approaches that generate both skeletally diversified tetracyclic peroxides and 6-aza-artemisinins. The anti-malarial activities of the tetracyclic peroxides with distinct skeletal arrays, however, were moderate and far inferior to artemisinins. Given the privileged scaffold of artemisinins, we next envisioned element implantation at the C6 position with a nitrogen without the trimmings of substituents and functional groups. This molecular design allowed the deep-seated structural modification of the hitherto unexplored cyclohexane moiety (C-ring) while keeping the three-dimensional structure of artemisinins. Notably, this approach induced dramatic changes of retrosynthetic transforms that allow an expeditious catalytic asymmetric synthesis with generation of substitutional variations at three sites (N6, C9, and C3) of the 6-aza-artemisinins. These de novo synthetic approaches led to the lead discovery with substantial intensification of the in vivo activities, which undermine the prevailing notion that the C-ring of artemisinins appears to be merely a structural unit but to be a functional area as the anti-malarial pharmacophore. Furthermore, we unexpectedly found that racemic 6-aza-artemisinin (33) exerted exceedingly potent in vivo efficacies superior to the chiral one and the first-line drug, artesunate.

Synthesis of the Antimalarial Peptide Aldehyde, a Precursor of Kozupeptin A, Utilizing a Designed Hydrophobic Anchor Molecule.

This Letter describes an efficient method of synthesizing highly bioactive peptide aldehydes without any concern about epimerization by liquid-phase peptide synthesis through the use of newly designed hydrophobic anchor molecules. Peptide elongation reactions effectively proceeded in less polar solvents, and direct crystallization by the addition of polar solvents enabled easy purification. This method also represents a new concept for the efficient synthesis of peptide derivatives. The development of new antimalarial drug candidates will be accelerated using this methodology.

Sarpeptins A and B, Lipopeptides Produced by Streptomyces sp. KO-7888 Overexpressing a Specific SARP Regulator.

Whole genome analysis of Streptomyces sp. KO-7888 has revealed various pathway-specific transcriptional regulatory genes associated with silent biosynthetic gene clusters. A Streptomyces antibiotic regulatory protein gene, speR, located adjacent to a novel nonribosomal peptide synthetase (NRPS) gene cluster, was overexpressed in the wild-type strain. The resulting recombinant strain of Streptomyces sp. KO-7888 produced two new lipopeptides, sarpeptins A and B. Their structures were elucidated by high-resolution electrospray ionization mass spectrometry, NMR analysis, and the advanced Marfey's method. The distinct modular sections of the corresponding NRPS biosynthetic gene cluster were characterized, and the assembly line for production of the lipopeptide chain was proposed.

Kozupeptins, Antimalarial Agents Produced by Paracamarosporium Species: Isolation, Structural Elucidation, Total Synthesis, and Bioactivity.

Kozupeptins A and B, novel antimalarial lipopeptides, were isolated from the culture broths of Paracamarosporium sp. FKI-7019. They exhibited potent antimalarial activity against chloroquine-sensitive and -resistant Plasmodium falciparum strains in vitro. The structural elucidation was accomplished by a combination of spectroscopic analyses and chemical approaches including a total synthesis of kozupeptin A. Synthetic kozupeptin A demonstrated a therapeutic effect in vivo, and an intermediate exhibited much higher antimalarial activity than kozupeptin A.

Pestynol, an Antifungal Compound Discovered Using a Saccharomyces cerevisiae 12geneΔ0HSR-iERG6-Based Assay.

The multidrug-sensitive budding yeast, Saccharomyces cerevisiae 12geneΔ0HSR-iERG6, is very useful in antifungal screens. A novel compound, named pestynol (1), was discovered from a culture of the fungus Pestalotiopsis humus FKI-7473 using the multidrug-sensitive yeast. The structure of 1 was elucidated by NMR studies and modified Mosher's method as (1 R,2 R,3 R,4 R)-( E)-5-(7,11-dimethyl-3-methylenedodeca-6,10-dien-1-yn-1-yl)cyclohex-5-ene-1,2,3,4-tetraol. Compound 1 showed antimicrobial activity against the Gram-positive bacteria, Klebsiella pneumoniae, and S. cerevisiae 12geneΔ0HSR-iERG6 and Mucor racemosus, but displayed only weak cytotoxicity against various human cancer cell lines. Compound 1 displayed antifungal activities against S. cerevisiae 12geneΔ0HSR-iERG6 and Mucor racemosus at 10 µg/disc.

Design and De Novo 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 de novo 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 in vivo antimalarial activities to artemisinin.

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 Staphylococcus aureus (MRSA) and vancomycin resistant enterococci (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.

Sucupiranins A-L, Furanocassane Diterpenoids from the Seeds of Bowdichia virgilioides.

Twelve new furanocassane diterpenoids, sucupiranins A-L (1-12), and three known compounds (13-15) were isolated from the seeds of Bowdichia virgilioides. The structures of the compounds were elucidated via 1H and 13C NMR analysis, including 2D NMR (1H-1H COSY, HSQC, HMBC, and NOESY); HRMS data; and X-ray crystallographic analysis. The absolute configurations were defined using their electronic circular dichroism (ECD) spectra by applying the exciton chirality method to the bis-p-bromobenzoate of compound 13. Sucupiranin J (10) inhibited lipopolysaccharide-induced nitric oxide production (IC50 30.6 µM), whereas sucupiranins J (10), K (11), and 13 exhibited weak antimalarial activity against Plasmodium falciparum K1 with IC50 values of 32.2, 23.5, and 22.9 µM and selectivity indices of 4.3, 1.9, and >12.0 (MRC-5/K1), respectively.

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).

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.

Proposal of Sphaerimonospora cavernae gen. nov., sp. nov. and transfer of Microbispora mesophila (Zhang et al., 1998) to Sphaerimonospora mesophila comb. nov. and Microbispora thailandensis (Duangmal et al., 2012) to Sphaerimonospora thailandensis comb. nov.

The actinomycete strain N74T, isolated from cave soil, was studied using a polyphasic taxonomic approach. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain N74T formed a stable, distinct lineage cluster together with Microbispora thailandensis NN276T (99.3% similarity) and Microbispora mesophila JCM 3151T (97.5%). Strain N74T was observed to produce single spherical spores on aerial mycelium as reported for M. mesophila JCM 3151T and M. thailandensis NN276T but different from other known species of the genus Microbispora, which are characterized by pairs of spores on aerial hyphae. Multilocus sequence analyses based on concatenated partial gyrB, rpoB, atpD, recA and 16S rRNA gene sequences showed a clear distinction of strain N74T, M. mesophila JCM 3151T and M. thailandensis NN276T from other members of the genus Microbispora, although the chemotaxonomic characteristics of strain N74T were similar to the genus Microbispora; the cell wall contained meso-diaminopimelic acid and the whole-cell hydrolysate contained madurose as the diagnostic sugar. The major menaquinone was MK-9(H4). The fatty acid profile contained iso-C16:0. On the basis of morphological, chemotaxonomic and phylogenetic evidence, strain N74T is assigned to a novel species of a new genus, for which the name Sphaerimonospora cavernae gen. nov., sp. nov. is proposed. The type strain of Sphaerimonospora cavernae is N74T (=BCC 77604T=NBRC 111481T). It is also proposed that M. mesophila and M. thailandensis be transferred to this genus as Sphaerimonospora mesophila comb. nov. (type strain JCM 3151T=NBRC 14179T=DSM 43048T) and Sphaerimonospora thailandensis comb. nov. (type strain NN276T=BCC 41490T=NBRC 107569T), respectively.

Purification of Shiga-like toxin 1 by pigeon egg white glycoproteins immobilized on Sepharose gels.

The galabiose structure Galalpha1-4Gal is rarely found in natural glycoproteins, but is abundantly present in pigeon egg white proteins as Galalpha(1-4)Galbeta(1-4)GlcNAc termini. Pigeon ovalbumin, ovomucoid, or the whole egg white were immobilized on periodate-oxidized Sepharose CL-6B gels by reductive amination. These gels were found to bind Shiga-like toxin type 1 (SLT-1) specifically and efficiently. SLT-1 was eluted from the gel beads with 0.5 M melibiose, which was more efficient and milder than elution with 4.5 M MgCl(2). SLT-1 was purified to homogeneity from the crude extract of Escherichia coli SLT100 expressing SLT-1 by a single affinity chromatographic step in 83-88% yield. The capacity of the gel was estimated to be ca. 1mg toxin/ml gel. Interestingly, SLT-2 was not bound by these affinity gels containing Galalpha1-4Galbeta1-4GlcNAc termini. Since SLT-2 has been shown to bind to Galalpha1-4Galbeta1-4Glc-terminating compounds, our results suggest that Glc in globotriose moiety is important for binding SLT-2, and replacing the Glc with GlcNAc in this triose renders it ineffective for binding SLT-2.