Carbon-11 radiolabeling of an oligopeptide containing tryptophan hydrochloride via a Pictet-Spengler reaction using carbon-11 formaldehyde

Copper-Mediated Radiocyanation of Unprotected Amino Acids and Peptides

This report describes a copper-mediated radiocyanation of aryl halides that is applicable to complex molecules. This transformation tolerates an exceptionally wide range of functional groups, including unprotected amino acids. As such, it enables the site-specific introduction of [¹¹C]CN into peptides at an iodophenylalanine residue. The use of a diamine-ligated copper(I) mediator is crucial for achieving high radiochemical yield under relatively mild conditions, thus limiting racemization and competing side reactions of other amino acid side chains. The reaction has been scaled and automated to deliver radiolabeled peptides, including analogues of adrenocorticotropic hormone 1-27 (ACTH) and nociceptin (NOP). For instance, this Cu-mediated radiocyanation was leveraged to prepare >40 mCi of [¹¹C]cyano-NOP to evaluate biodistribution in a primate using positron emission tomography. This investigation provides preliminary evidence that nociceptin crosses the blood-brain barrier and shows uptake across all brain regions (SUV > 1 at 60 min post injection), consistent with the known distribution of NOP receptors in the rhesus brain.

Special radionuclide production activities – recent developments at QST and throughout Japan

National Institutes for Quantum Science and Technology (QST), formerly known as the National Institute of Radiological Sciences (NIRS), has been engaged in work on radiopharmaceutical science using cyclotrons since 1974. Eight pioneering researchers founded the basis of this field of research at NIRS, and to the present, many researchers and technicians have accumulated both scientific and technical achievements, as well as inherited the spirit of research. Besides, in recent years, we have developed production systems with AVF-930 cyclotron for various ‘non-standard’ radioisotopes applied in both diagnosis and therapy. Here, we review the past 50 years of our activities on radioisotope and radiopharmaceutical development, as well as more recent activities.

The Pictet-Spengler Reaction Updates Its Habits

The Pictet-Spengler reaction (P-S) is one of the most direct, efficient, and variable synthetic method for the construction of privileged pharmacophores such as tetrahydro-isoquinolines (THIQs), tetrahydro-β-carbolines (THBCs), and polyheterocyclic frameworks. In the lustro (five-year period) following its centenary birthday, the P-S reaction did not exit the stage but it came up again on limelight with new features. This review focuses on the interesting results achieved in this period (2011-2015), analyzing the versatility of this reaction. Classic P-S was reported in the total synthesis of complex alkaloids, in combination with chiral catalysts as well as for the generation of libraries of compounds in medicinal chemistry. The P-S has been used also in tandem reactions, with the sequences including ring closing metathesis, isomerization, Michael addition, and Gold- or Brønsted acid-catalyzed N-acyliminium cyclization. Moreover, the combination of P-S reaction with Ugi multicomponent reaction has been exploited for the construction of highly complex polycyclic architectures in few steps and high yields. The P-S reaction has also been successfully employed in solid-phase synthesis, affording products with different structures, including peptidomimetics, synthetic heterocycles, and natural compounds. Finally, the enzymatic version of P-S has been reported for biosynthesis, biotransformations, and bioconjugations.

Direct 11CN-Labeling of Unprotected Peptides via Palladium-Mediated Sequential Cross-Coupling Reactions

A practical procedure for ¹¹CN-labeling of unprotected peptides has been developed. The method was shown to be highly chemoselective for cysteine over other potentially nucleophilic residues, and the radiolabeled products were synthesized and purified in less than 15 min. Appropriate for biomedical applications, the method could be used on an extremely small scale (20 nmol) with a high radiochemical yield. The success of the protocol stems from the use of a Pd-reagent based on a dihaloarene, which enables direct "nucleophile-nucleophile" coupling of the peptide and [¹¹C]cyanide by temporal separation of nucleophile addition.