Facile synthesis and evaluation of C-functionalized benzyl-1-oxa-4,7,10-triazacyclododecane-N,N′,N″-triacetic acid as chelating agent for 111In-labeled polypeptides

Synthesis and evaluation of a para-carboxylated benzyl-DOTA for labeling peptides and polypeptides

INTRODUCTION

Radiolabeled peptides and low-molecular-weight (LMW) polypeptides show high and persistent radioactivity levels in the kidney. To develop a DOTA-based bifunctional chelating agent that provides a radiometabolite with a rapid elimination rate from the kidney, a para-carboxyl Bn-DOTA (p-COOH-Bn-DOTA) was designed, synthesized, and evaluated.

METHODS

A precursor compound, p-COOH-Bn-DOTA(^tBu)₄, was synthesized in 9 steps using N-Boc-p-iodo-L-phenylalanine as the starting material. A synthetic somatostatin analog (TOC) was used as a representative peptide metabolized in the renal lysosomes. p-COOH-Bn-DOTA-conjugated TOC (DOTA-Bn-TOC) was synthesized by the conventional solid-phase peptide synthesis using p-COOH-Bn-DOTA(^tBu)₄. DOTA-tris(^tBu ester) was also conjugated with TOC to prepare DOTATOC. ¹¹¹In-labeling of the peptides was conducted under similar conditions. The radiochemical conversions, stability against apo-transferrin (apoTf), and in vivo behaviors were compared.

RESULTS

[¹¹¹In]In-DOTA-Bn-TOC was obtained with higher radiochemical conversions than [¹¹¹In]In-DOTATOC. Both ¹¹¹In-labeled TOC derivatives remained stable against apoTf. In biodistribution studies, [¹¹¹In]In-DOTA-Bn-TOC exhibited higher initial uptake in the kidney, followed by a faster elimination rate of radioactivity into the urine than [¹¹¹In]In-DOTATOC. The metabolic studies showed that the shorter residence time of the radiometabolite from [¹¹¹In]In-DOTA-Bn-TOC was responsible for the renal radioactivity decline.

CONCLUSION

p-COOH-Bn-DOTA provides stable ¹¹¹In-labeled peptides in high yields at low peptide concentrations. p-COOH-Bn-DOTA also provides a radiometabolite with a short residence time in the kidney. Such characteristics would render p-COOH-Bn-DOTA useful to the future application to radiolabeled LMW polypeptides with low renal radioactivity levels.

Peptoids as tools and sensors

A review of molecular tools and sensors assembled on N-substituted glycine, or α-peptoid, oligomers between 2013 and November 2018 with the following sections: (a) Peptoids as crystal growth modifiers, (b) Peptoids as catalysts, (c) Ion and molecule sequestration and transport, (d) Peptoid sensors, (e) Macromolecule recognition, (f) Cellular transporters, (g) Medical imaging, (h) Future direction and (i) Summary and outlook. Peptoids are a promising class of peptide mimic making them an excellent platform for functional molecule preparation. Attributes of peptoid oligomers include: (a) the ease of precise sequence definition and mono-dispersity; (b) access to a vast chemical space within simple and repeating chemical preparative steps and (c) thermal, chemical and biological stability all lending support for their application in a number of areas, with some that have been realised to date. The peptoid tool and sensor examples selected have realised practical utility. They serve to illustrate the rapidity of new insight that can generate in many disparate areas of science and technology, enabling the quick assembly of design criteria for efficient peptoid molecular tools and sensors.

Tailoring Bicelle Morphology and Thermal Stability with Lanthanide-Chelating Cholesterol Conjugates

Bicelles composed of DMPC and phospholipids capable of chelating lanthanide ions, such as 1,2-dimyristoyl-sn-glycero-3-phospho-ethanolamine-diethylene triaminepentaacetate (DMPE-DTPA), are highly tunable magnetically responsive soft materials. Further doping of these systems with cholesterol-DTPA conjugates complexed to a lanthanide ion considerably enhances the bicelle's size and magnetic alignability. The high value of these cholesterol conjugates for bicelle design remains largely unexplored. Herein, we examine how molecular structural alterations within the cholesterol-DTPA conjugates lead to contrasting self-assembled polymolecular aggregate structures when incorporated into DMPC/DMPE-DTPA/Tm(3+) bilayers. The nature of the linker connecting the DTPA-chelating moiety to the sterol backbone is examined by synthesizing conjugates of various linker lengths and polarities. The incorporation of these compounds within the bilayer results in polymolecular aggregate geometries of higher curvature. The increasing degrees of freedom for conformational changes conveyed to the chelator headgroup with increasing linker atomic length reduce the cholesterol-DTPA conjugate's critical packing parameter. Consequently, an inverse correlation between the number of carbon atoms in the linker and the bicelle radius is established. The introduction of polarity into the carbon chain of the linker did not cause major changes in the polymolecular aggregate architecture. Under specific conditions, the additives permit the formation of remarkably temperature-resistant bicelles. The versatility of design offered by these amphiphiles gives rise to new and viable tools for the growing field of magnetically responsive soft materials.