A bis-boron boramino acid PET tracer for brain tumor diagnosis

PURPOSE

Boramino acids are a class of amino acid biomimics that replace the carboxylate group with trifluoroborate and can achieve the 18F-labeled positron emission tomography (PET) and boron neutron capture therapy (BNCT) with identical chemical structure.

METHODS

This study reports a trifluoroborate-derived boronophenylalanine (BBPA), a derived boronophenylalanine (BPA) for BNCT, as a promising PET tracer for tumor imaging.

RESULTS

Competition inhibition assays in cancer cells suggested the cell accumulation of [18F]BBPA is through large neutral amino acid transporter type-1 (LAT-1). Of note, [18F]BBPA is a pan-cancer probe that shows notable tumor uptake in B16-F10 tumor-bearing mice. In the patients with gliomas and metastatic brain tumors, [18F]BBPA-PET shows good tumor uptake and notable tumor-to-normal brain ratio (T/N ratio, 18.7 ± 5.5, n = 11), higher than common amino acid PET tracers. The [18F]BBPA-PET quantitative parameters exhibited no difference in diverse contrast-enhanced status (P = 0.115-0.687) suggesting the [18F]BBPA uptake was independent from MRI contrast-enhancement.

CONCLUSION

This study outlines a clinical trial with [18F]BBPA to achieve higher tumor-specific accumulation for PET, provides a potential technique for brain tumor diagnosis, and might facilitate the BNCT of brain tumors.

Highly stereoselective synthesis of spirocyclopropylthiooxindoles and biological evaluation

We present a novel highly stereoselective Rh-catalyzed cyclopropanation of diazothiooxindoles with a broad range of α-functionalized styrenes, enabling facile access of chiral spirocyclopropylthiooxindoles in high to excellent enantiomeric excess.

Me2(CH2CH)SiCN: a bifunctional ethylene equivalent for Diels–Alder reaction based controllable tandem synthesis

A bifunctional silyl reagent Me₂(CH₂CH)SiCN has been developed as a novel ethylene equivalent for the Diels–Alder (DA) reaction. The use of this reagent enables the controllable synthesis of value-added cyclohexenyl ketones or 2-acyl cyclohexancarbonitrile derivatives through a five- or six-step tandem sequence based on a Wittig/cyanosilylation/DA reaction/retro-cyanosilylation/isomerization sequence that involves a temporary silicon-tethered intramolecular DA reaction.

We report an unprecedented tandem Wittig/cyanosilylation/DA reaction/retro-cyanosilylation/isomerization sequence by using our designed bifunctional ethylene equivalent Me₂(CH₂CH)SiCN.

Organocatalytic enantioselective reactions involving prochiral carbocationic intermediates

Since the discovery of carbocations in 1901, the past 120 years have witnessed many marvelous advances in the chemistry of carbocations. The state-of-the-art research in this field is to overcome the intrinsic instability and high reactivity of the prochiral carbocationic intermediates to develop catalytic asymmetric reactions. Such transformations enable the facile synthesis of structurally diverse value-added products from readily available starting materials such as alkenes, alcohols, and carbonyl derivatives, and enjoy high and even perfect atom-economy in most cases. Notably, such allows catalytic stereoconvergent synthesis from racemic substrates and can realize regioselectivity in olefin functionalization reactions complementary to radical processes. With the rapid developments in modern asymmetric organocatalysis, a variety of highly enantioselective protocols evolving prochiral carbocationic intermediates have been achieved by employing three strategies, namely chiral ion-pairing, chiral nucleophile, or chiral carbenium ion strategy. This feature article aims to summarize the exciting advances in this emerging area and briefly showcase the possible mechanisms. The advantages and limitations of each strategy are presented as well as their synthetic applications in the synthesis of natural products or bioactive compounds.

Modular synthesis of chiral 1,2-dihydropyridines via Mannich/Wittig/cycloisomerization sequence that internally reuses waste

1,2-Dihydropyridines are valuable and reactive synthons, and particularly useful precursors to synthesize piperidines and pyridines that are among the most common structural components of pharmaceuticals. However, the catalytic enantioselective synthesis of structurally diverse 1,2-dihydropyridines is limited to enantioselective addition of nucleophiles to activated pyridines. Here, we report a modular organocatalytic Mannich/Wittig/cycloisomerization sequence as a flexible strategy to access chiral 1,2-dihydropyridines from N-Boc aldimines, aldehydes, and phosphoranes, using a chiral amine catalyst. The key step in this protocol, cycloisomerization of chiral N-Boc δ-amino α,β-unsaturated ketones recycles the waste to improve the yield. Specifically, recycling by-product water from imine formation to gradually release the true catalyst HCl via hydrolysis of SiCl₄, whilst maintaining a low concentration of HCl to suppress side reactions, and reusing waste Ph₃PO from the Wittig step to modulate the acidity of HCl. This approach allows facile access to enantioenriched 2-substituted, 2,3- or 2,6-cis-disubstituted, and 2,3,6-cis-trisubstituted piperidines.