Short and versatile route to a key intermediate for lactacystin synthesis

Synthesis of Tetramic Acid Derivatives via a Tandem Umpolung Alkylation/Reduction/Cyclization Reaction of γ-Hydrazono β-Ketoester

An efficient method for the one-pot synthesis of tetramic acid derivatives was developed utilizing tandem umpolung N-alkylation/reduction/cyclization of γ-hydrazono β-ketoester. By using this reaction as a key step, the total synthesis of the 3-spiro 7-hydroxamic acid tetralin which possesses an HDAC inhibitory activity was also achieved.

Tropane alkaloids biosynthesis involves an unusual type III polyketide synthase and non-enzymatic condensation

The skeleton of tropane alkaloids is derived from ornithine-derived N-methylpyrrolinium and two malonyl-CoA units. The enzymatic mechanism that connects N-methylpyrrolinium and malonyl-CoA units remains unknown. Here, we report the characterization of three pyrrolidine ketide synthases (PYKS), AaPYKS, DsPYKS, and AbPYKS, from three different hyoscyamine- and scopolamine-producing plants. By examining the crystal structure and biochemical activity of AaPYKS, we show that the reaction mechanism involves PYKS-mediated malonyl-CoA condensation to generate a 3-oxo-glutaric acid intermediate that can undergo non-enzymatic Mannich-like condensation with N-methylpyrrolinium to yield the racemic 4-(1-methyl-2-pyrrolidinyl)-3-oxobutanoic acid. This study therefore provides a long sought-after biosynthetic mechanism to explain condensation between N-methylpyrrolinium and acetate units and, more importantly, identifies an unusual plant type III polyketide synthase that can only catalyze one round of malonyl-CoA condensation.

Tropane alkaloids are medicinally significant plant metabolites generated by an unusual condensation of ornithine-derived and malonyl-CoA precursors. Here, Huang et al. show that pyrrolidine ketide synthase catalyzes a single round of condensation, which is followed by a non-enzymatic Mannich-like condensation.

Formal synthesis of (+)-lactacystin from l-serine

A formal, stereocontrolled synthesis of lactacystin has been completed from t-Bu-O-l-serine, providing the key intermediate 13, also useful for the generation of a range of C-9 analogues.

A formal, stereocontrolled synthesis of lactacystin has been completed from t-Bu-O-l-serine.

Ag NPs decorated on a COF in the presence of DBU as an efficient catalytic system for the synthesis of tetramic acids via CO2 fixation into propargylic amines at atmospheric pressure

Ag NPs are decorated at the surface of a COF material TpPa-1 and the resulting Ag@TpPa-1 catalyzes efficiently for the synthesis of tetramic acids from a variety of propargylic amines using CO₂ as reagent.

Synthesis of a leopolic acid-inspired tetramic acid with antimicrobial activity against multidrug-resistant bacteria

The increasing emergence of multidrug-resistant pathogens is one of the biggest threats to human health and food security. The discovery of new antibacterials, and in particular the finding of new scaffolds, is an imperative goal to stay ahead of the evolution of antibiotic resistance. Herein we report the synthesis of a 3-decyltetramic acid analogue of the ureido dipeptide natural antibiotic leopolic acid A. The key step in the synthetic strategy is an intramolecular Lacey–Dieckmann cyclization reaction of a linear precursor to obtain the desired 3-alkyl-substituted tetramic acid core. The synthesized analogue is more effective than the parent leopolic acid A against Gram-positive (Staphylococcus pseudintermedius) and Gram-negative (E. coli) bacteria (MIC 8 µg/mL and 64 µg/mL, respectively). Interestingly, the compound shows a significant activity against Staphylococcus pseudintermedius strains expressing a multidrug-resistant phenotype (average MIC 32 µg/mL on 30 strains tested). These results suggest that this molecule can be considered a promising starting point for the development of a novel class of antibacterial agents active also against resistant strains.

Novel method of tetramic acid synthesis: silver-catalyzed carbon dioxide incorporation into propargylic amine and intramolecular rearrangement

Tetramic acid derivatives have been studied as biologically active heterocycle structures for pharmaceutical or agricultural chemicals. Conventional preparative approaches often require highly functionalized starting materials and harsh heating conditions in basic media. The present report provides a conceptually new synthetic strategy for the synthesis of tetramic acid derivatives from easily available propargylic amines and carbon dioxide with a silver salt and DBU under mild reaction conditions.

Neurotrophic natural products: chemistry and biology

Neurodegenerative diseases and spinal cord injury affect approximately 50 million people worldwide, bringing the total healthcare cost to over 600 billion dollars per year. Nervous system growth factors, that is, neurotrophins, are a potential solution to these disorders, since they could promote nerve regeneration. An average of 500 publications per year attests to the significance of neurotrophins in biomedical sciences and underlines their potential for therapeutic applications. Nonetheless, the poor pharmacokinetic profile of neurotrophins severely restricts their clinical use. On the other hand, small molecules that modulate neurotrophic activity offer a promising therapeutic approach against neurological disorders. Nature has provided an impressive array of natural products that have potent neurotrophic activities. This Review highlights the current synthetic strategies toward these compounds and summarizes their ability to induce neuronal growth and rehabilitation. It is anticipated that neurotrophic natural products could be used not only as starting points in drug design but also as tools to study the next frontier in biomedical sciences: the brain activity map project.

Biosynthesis of HSAF, a tetramic acid-containing macrolactam from Lysobacter enzymogenes

HSAF was isolated from Lysobacter enzymogenes , a bacterium used in the biological control of fungal diseases of plants. Structurally, it is a tetramic acid-containing macrolactam fused to a tricyclic system. HSAF exhibits a novel mode of action by disrupting sphingolipids important to the polarized growth of filamentous fungi. Here we describe the HSAF biosynthetic gene cluster, which contains only a single-module polyketide synthase/nonribosomal peptide synthetase (PKS/NRPS), although the biosynthesis of HSAF apparently requires two separate polyketide chains that are linked together by one amino acid (ornithine) via two amide bonds. Flanking the PKS/NRPS are six genes that encoding a cascade of four tightly clustered redox enzymes on one side and a sterol desaturase/fatty acid hydroxylase and a ferredoxin reductase on the other side. The genetic data demonstrate that the four redox genes, in addition to the PKS/NRPS gene and the sterol desaturase/fatty acid hydroxylase gene, are required for HSAF production. The biochemical data show that the adenylation domain of the NRPS specifically activates L-ornithine and that the four-domain NRPS is able to catalyze the formation of a tetramic acid-containing product from acyl-S-ACP and ornithinyl-S-NRPS. These results reveal a previously unrecognized biosynthetic mechanism for hybrid PK/NRP in prokaryotic organisms.

Evaluation of the bioactivity of novel spiroisoxazoline typecompounds against normal and cancer cell lines

The aim of this study was to investigate the in vitro cellular activity of novel spiroisoxazoline type compounds against normal and cancer cell lines from lung tissue (Hs888Lu), neuron-phenotypic cells (SH-SY5Y), neuroblastoma (SH-SY5Y), human histiocytic lymphoma (U937), lung cancer (A549), and leukaemia (HL-60). Our bioassay program revealed that the spiroisoxazoline type compounds show cytotoxicity only in lymphoma cell lines, which is in contrast with the pyrrolidine precursor of these spiroisoxazoline compounds, where significant cytotoxicity is seen in all normal and cancer cell lines. These data suggest a tumour-specific mechanism of action. In addition these data also show that spiroisoxazoline compounds are non-toxic in the human neuronphenotypic neuroblastoma SH-SY5Y cell line, and furthermore that they might protect cells from neurodegenerative disease.

Synthesis of 2,3-dioxo-5-(substituted)-arylpyrroles and their 2-oxo-5-aryl-3-hydrazone pyrrolidine derivatives

Some novel 2,3-dioxo-5-(substituted)arylpyrroles have been synthesized. Among these, pyrrolidine compound 1b was converted to 2,3-dioxo-5-aryl pyrrolidine 2b. Finally a set of hydrazone derivatives was obtained from the reaction of 2b with various hydrazine salts. The structures of all the new synthesized compounds were confirmed by elemental analyses, IR and ¹H-NMR spectra.

A formal synthesis of (+)-lactacystin

A synthetic route to the neurotrophic agent (+)-lactacystin has been developed utilizing a base-promoted intramolecular alkylidenecarbene C-H insertion as the key transformation.