Semi-synthesis and structure-activity relationship study yield antibacterial vicenistatin derivatives with low cytotoxicity

Vicenistatin (1) is a 20-membered polyketide macrocyclic antibiotic with potent antimicrobial and cytotoxic activities. In this study, to further explore the potential of 1 as candidates of antibacterial drug development, 4'-N-demethyl vicenistatin (2), a secondary metabolite obtained from the ∆vicG mutant strain of Monodonata labio-associated Streptomyces parvus SCSIO Mla-L010, was utilized as a starting material for modifications of 4'-amino group of vicenistatin. Six new vicenistatin derivatives (3-8) were semi-synthesized through a concise route of amino modification with various aliphatic and aromatic aldehydes. Our study reveals that the bioactivity of vicenistatin is closely related to amino modification in sugar moiety, which results from the length of alkyl side chain as well as the presence of electron withdrawing/denoting group on the benzene ring. Importantly, compounds 4 with a butyl group and 8 with a 3,5-dihydroxyl-benzyl group at 4'-amino group, respectively, exhibited good antimicrobial activities, with MIC values spanning 0.5-4 μg ml-1 to Gram-positive pathogens, including methicillin-resistant Staphylococcus aureus, methicillin-resistant Staphylococcus epidermidis, Micrococcus luteus and Bacillus subtilis, with low cytotoxicity. This research promotes the further exploration of structure-activity relationships of vicenistatin and provides new vicenistatin derivatives for development of future anti-infectious agents with reduced cytotoxicity.

PEGylated and Acylated Elabela Analogues Show Enhanced Receptor Binding, Prolonged Stability, and Remedy of Acute Kidney Injury

Acute kidney injury (AKI), mostly caused by renal ischemia-reperfusion (I/R) injury and nephrotoxins, is characterized by rapid deterioration in renal-functions without effective drug treatment available. Through activation of a G protein-coupled receptor APJ, a furin-cleaved fragment of Elabela (ELA[22-32], E11), an endogenous APJ ligand, protects against renal I/R injury. However, the poor plasma stability and relatively weak APJ-binding ability of E11 limit its application. To address these issues, we rationally designed and synthesized a set of E11 analogues modified by palmitic acid (Pal) or polyethylene glycol; improved plasma stability and APJ-binding capacity of these analogues were achieved. In cultured renal tubular cells, these analogues protected against hypoxia-reperfusion or cisplatin-caused injury. For renal I/R-injured mice, these analogues showed improved reno-protective effects than E11; notably, Pal-E11 showed therapeutic effects at 24 h post I/R injury. These results present ELA analogues as potential therapeutic options in managing AKI.

Natural polyenic macrolactams and polycyclic derivatives generated by transannular pericyclic reactions: optimized biogenesis challenging chemical synthesis

Covering from 1992 to the end of 2020-11-20.Genetically-encoded polyenic macrolactams, which are constructed by Nature using hybrid polyketide synthase/nonribosomal peptide synthase (PKSs/NRPSs) assembly lines, are part of the large collection of natural products isolated from bacteria. Activation of cryptic (i.e., silent) gene clusters in these microorganisms has more recently allowed to generate and eventually isolate additional members of the family. Having two unsaturated fragments separated by short saturated chains, the primary macrolactam is posited to undergo transannular reactions and further rearrangements thus leading to the generation of a structurally diverse collection of polycyclic (natural) products and oxidized derivatives. The review will cover the challenges that scientists face on the isolation of these unstable compounds from the cultures of the producing microorganisms, their structural characterization, biological activities, optimized biogenetic routes, as well as the skeletal rearrangements of the primary structures of the natural macrolactams derived from pericyclic reactions of the polyenic fragments. The efforts of the synthetic chemists to emulate Nature on the successful generation and structural confirmation of these natural products will also be reported.

Application of The Dess-Martin Oxidation in Total Synthesis of Natural Products

Dess-Martin periodinane (DMP), a commercially available chemical, is frequently utilized as a mild oxidative agent for the selective oxidation of primary and secondary alcohols to their corresponding aldehydes and ketones, respectively. DMP shows several merits over other common oxidative agents such as chromiumand DMSO-based oxidants; thus, it is habitually employed in the total synthesis of natural products. In this review, we try to underscore the applications of DMP as an effective oxidant in an appropriate step (steps) in the multi-step total synthesis of natural products.

Asymmetric total synthesis of (+)-astellatol and (−)-astellatene

Here we describe the full account of the total synthesis of (+)-astellatol, as well as the first total synthesis of (−)-astellatene.

Total Synthesis of Astellatol

A nearly-30-year-old unanswered synthetic puzzle, astellatol, has been solved in an enantiospecific manner. The highly congested pentacyclic skeleton of this rare sesterterpenoid, which possesses a unique bicyclo[4.1.1]octane motif, ten stereocenters, a cyclobutane that contains two quaternary centers, an exo-methylene group, and a sterically encumbered isopropyl trans-hydrindane motif, makes astellatol arguably one of the most challenging targets for sesterterpenoid synthesis. An intramolecular Pauson-Khand reaction was exploited to construct the right-hand side scaffold of this sesterterpenoid. An unprecedented reductive radical 1,6-addition, mediated by SmI₂ , forged the cyclobutane motif. Last, a strategic oxidation/reduction step provided not only the decisive solution for the remarkably challenging late-stage transformations, but also a highly valuable unravelling of the notorious issue of trans-hydrindane synthesis. Importantly, the synthesis of astellatol showcases a rapid, scalable strategy to access diverse complex isopropyl trans-hydrindane sesterterpenoids.

O-Glycosylation methods in the total synthesis of complex natural glycosides

We highlight the total syntheses of 33 complex natural O-glycosides, with a particular focus on the O-glycosylation methods that enable the connection of the saccharides and aglycones.

Systematic comparison of sets of (13)C NMR spectra that are potentially identical. Confirmation of the configuration of a cuticular hydrocarbon from the cane beetle Antitrogus parvulus

A systematic process is introduced to compare (13)C NMR spectra of two (or more) candidate samples of known structure to a natural product sample of unknown structure. The process is designed for the case where the spectra involved can reasonably be expected to be very similar, perhaps even identical. It is first validated by using published (13)C NMR data sets for the natural product 4,6,8,10,16,18-hexamethyldocosane. Then the stereoselective total syntheses of two candidate isomers of the related 4,6,8,10,16-pentamethyldocosane natural product are described, and the process is applied to confidently assign the configuration of the natural product as (4S,6R,8R,10S,16S). This is accomplished even though the chemical shift differences between this isomer and its (16R)-epimer are only ±5-10 ppb (±0.005-0.01 ppm).

Carbon-carbon bonding made easy

The palladium-catalyzed cross-coupling reaction between organoboranes and organic electrophiles in the presence of base was first developed 30 years ago. It offers a powerful and general methodology for forming carbon-carbon bonds. The scope of the reaction has continued to evolve and broaden to meet modern synthetic requirements.

SuperQuat N-acyl-5,5-dimethyloxazolidin-2-ones for the asymmetric synthesis of alpha-alkyl and beta-alkyl aldehydes

The proclivity of alpha-branched N-2'-benzyl-3'-phenylpropionyl derivatives of (S)-4-benzyl-5,5-dimethyl-, (S)-4-phenyl-5,5-dimethyl-, (S)-4-isopropyl-5,5-dimethyl-, (S)-4-benzyl- and (S)-4-benzyl-5,5-diphenyl-oxazolidin-2-ones to generate directly 2-benzyl-3-phenylpropionaldehyde upon hydride reduction with DIBAL is investigated. The (S)-4-benzyl-5,5-dimethyl-derivative proved optimal for inhibition of endocyclic nucleophilic attack, giving 2-benzyl-3-phenylpropionaldehyde in good yield upon reduction. Application of this methodology for the asymmetric synthesis of chiral aldehydes via diastereoselective enolate alkylation of a range of (S)-N-acyl-4-benzyl-5,5-dimethyloxazolidin-2-ones to afford and array of alpha-substituted-N-acyl-5,5-dimethyloxazolidin- 2-ones (85-94% de) and subsequent reduction with DIBAL afforded directly non-racemic alpha-substituted aldehydes without loss of stereochemical integrity (87-94% ee). The extension of this protocol for the asymmetric synthesis of beta-substituted aldehydes is demonstrated, via the diastereoselective conjugate addition of a range of organocuprates to (S)-N-acyl-4-phenyl-5,5-dimethyloxazolidin-2-ones which proceeds with high diastereoselectivity (generally > 95% de). Reduction of the conjugate addition products with DIBAL gives non-racemic beta-substituted aldehydes in high yields and in high ee (generally > 95% ee). This methodology is exemplified by the asymmetric synthesis of (R)-3-isopropenylhept-6-enal, which has previously been used in the synthesis of (3Z,6R)-3-methyl-6-isopropenyl-3,9-decadien-1-yl acetate, a component of the sex pheromones of the California red scale.