Several synthetic materials exhibiting contrast imaging properties have become vital to the field of biomedical imaging. Polymeric biomaterials and metals are commonly used imaging agents and can assist in the monitoring of therapy response, migration, degradation, changes in morphology, defects, and image-guided surgery. In comparison to metals, most bio and synthetic polymers lack inherent imaging properties. Polymeric biomaterials, specifically polyesters, have gained a considerable amount of attention due to their unique properties including biocompatibility, biodegradation, facile synthesis, and modification capability. Polyester implants and nanomaterials are available on the market or are in clinical trials for many applications including: dental implants, cranio-maxilofacial implants, soft tissue sutures and staples, abdominal wall repair, tendon and ligament reconstruction, fracture fixation devices, and coronary drug eluting stents. This review aims to provide a summary of the recent developments of polyesters with bioimaging contrast properties. The three main approaches to prepare bioimaging polyesters (coating, encapsulation, and functionalization) are discussed in depth. Furthermore, commonly used imaging modalities including X-ray computed tomography, magnetic resonance imaging, ultrasound, fluorescence, and radionucleotide polyester contrast agents are highlighted. In each section, examples of impactful bioimaging polyesters in the five major imaging modalities are evaluated.

A formal [2 + 2] cycloaddition of 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) with electron-rich alkynyl sulfides and selenides is described. These investigations provide a convenient method to access diazacyclobutenes in good yield while tolerating a relatively broad substrate scope of thio-acetylenes. This method provides ready access to a unique and hitherto rarely accessible class of heterocycles. A combination of dynamic NMR, X-ray crystallography, and computation sheds light on the potential aromaticity of the scaffold.

A series of rate studies were conducted to evaluate the steric and electronic properties that govern the reactivity of iodoarene amide catalysts in the α-oxytosylation of propiophenone. A meta-substituted benzamide catalyst emerged as the most reactive. This catalyst was employed in the α-oxytosylation of a series of substituted propiophenones, returning the α-tosyloxy ketone products in excellent isolated yield.

Synthetic materials exhibiting contrast imaging properties have become vital to the field of biomedical imaging. However, polymeric biomaterials are lacking imaging contrast properties for deep tissue imaging. this report details the synthesis and characterization of a suite of aryl-iodo monomers, which were used to prepare iodinated polyesters using a pre-functionalization approach. commercially available 4-iodo-phenylalanine or 4-iodobenzyl bromide served as the starting materials for the synthesis of three iodinated monomeric moieties (a modified lactide, morpholine-2,5-dione, and caprolactone), which under a tin-mediated ring-opening polymerization (Rop), generated their respective polyesters (pe) or poly(ester amides) (peA). An increase in X-ray intensity of all synthesized iodine-containing polymers, in comparison to non-iodinated poly(lactic acid) (pLA), validated their functionality as radio-opaque materials. the iodinated-poly(lactic acid) (ipLA) material was visualized through varying thicknesses of chicken tissue, thus demonstrating its potenial as a radio-opaque biomaterial. Medical imaging, a technique that provides structural visualization inside the body, aides in the study of specific morphological changes within living and nonliving systems 1,2. One particular imaging modality, X-ray radiography, is frequently used as a diagnostic tool for non-invasive, in vivo, real-time examinations of three-dimensional opaque objects. X-ray imaging can be used to monitor response, degradation, and defects of biomedical devices 3. Concerns over the long-term stability of prolonged or permanent implantable devices have led to the development of polyester-based materials due to their desirable properties (i.e. biocompatibility, biodegradability, and facile synthesis) 4-8. The evolution of biodegradable polyester devices, like staples, stents, sutures, and implants, have had a significant impact on the biomedical field 4,9,10. Perhaps the most noteworthy advantage is their ability to be degraded and excreted from the body, obviating the need for their removal or surgical revision. This can be vital in major surgical procedures such as fracture fixation, spinal fixation, and abdominal wall repair 4,10. While commercially available polyester devices have seen a considerable amount of use in the biomedical field, their in vivo performance can be difficult to predict and evaluate due to the complex biological environment associated with tissues 10,11. Therefore, the real-time monitoring of these devices is critical in order to understand their performance and fate in the body. The major drawback of polyester-based devices is that they lack inherent contrast imaging properties, making it difficult to visualize the area of interest. Imaging techniques are useful only when the intensity of a signal is sufficient enough to distinguish the target from surrounding tissues or materials. This issue becomes even more evident when imaging materials through deep tissue or when monitoring minor defects in biomaterials 12. Recent ...

The α-oxidized thioimidates are useful bidentate ligands and are important motifs in pharmaceuticals, pesticides, and fungicides. Despite their broad utility, a direct route for their synthesis has been elusive. Herein, we describe a one-step synthesis of N,Ndicarbamoyl 2-iminothioimidates from easily accessible thioacetylenes and commercially available azodicarboxylates (20 examples, ≤99% yield). Additionally, the mechanism of the transformation was extensively explored by variable-temperature NMR, in situ IR, and quantum mechanical simulations. These experiments suggest that the reaction commences with a highly asynchronous [2 + 2] cycloaddition, which leads to a four-membered diazacyclobutene intermediate with a barrier consistent with the observed reaction rate. This intermediate was then isolated for subsequent kinetic measurements, which yielded an experimental barrier within 1 kcal/mol of the calculated barrier for a subsequent 4π electrocyclic ring opening leading to the observed iminothioimidate products. This method represents the first direct route to α-oxidized thioimidates from readily accessible starting materials.

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