Radiosynthesis of [13N]dantrolene, a positron emission tomography probe for breast cancer resistant protein, using no-carrier-added [13N]ammonia

Synthesis, X-ray crystallography and antimicrobial activity of 2-cyanoguanidinophenytoin

The optimized synthesis of [5-oxo-4,4-diphenylimidazolidin-2-ylidene]cyanamide, which is known as 2-cyanoguanidinophenytoin (CNG-DPH) (3), and (imidazo[4,5-d]imidazole-2,5-diylidine)dicyanamide (4) has been reported in the present work. Furthermore, new Mannich bases derived from CNG-DPH were synthesized via its reaction with formaldehyde and using the corresponding amines, piperidine (base 5), and morpholine (base 6). Also, the antimicrobial activity and X-ray crystal structures for CNG-DPH and their Mannich bases were studied. The bases 3 and 6 crystallized in a monoclinic system; the crystal structure of 3 containing four molecules in the unit cell with a P21/c space group. The unit cell of 6 has eight molecules with a C2/c space group. The inter and intra hydrogen bond contacts packed and stabilized both of the structures. The morpholine ring of base 6 demonstrated a distinctive chair configuration. Mannich bases 5 and 6 showed promising antimicrobial effects. base 4 has a greater percentage for in vitro cytotoxicity (IC50) against normal cells, whereas 3 has the lowest ratio.

A decade review of triphosgene and its applications in organic reactions

This review article highlights selected advances in triphosgene-enabled organic synthetic reactions that were reported in the decade of 2010-2019. Triphosgene is a versatile reagent in organic synthesis. It serves as a convenient substitute for the toxic phosgene gas. Despite its first known preparation in the late 19th interestingly began only three decades ago. Despite the relatively short history, triphosgene has been proven to be very useful in facilitating the preparation of a vast scope of value-added compounds, such as organohalides, acid chlorides, isocyanates, carbonyl addition adducts, heterocycles, among others. Furthermore, applications of triphosgene in complex molecules synthesis, polymer synthesis, and other techniques, such as flow chemistry and solid phase synthesis, have also emerged in the literature.

Connective synthesis of 5,5-disubstituted hydantoins by tandem α-amination and α-arylation of silyl ketene acetals

Amination of a silylated ester generates an intermediate urea that transfers an aryl ring to the aminated centre and cyclises to a hydantoin.

5,5-Disubstituted hydantoins, formally the cyclisation products of quaternary amino acids, were formed connectively from simple ester-derived starting materials by a one-pot tandem method. Amination of the silyl ketene acetal derivative of a methyl ester takes place by silver-catalysed addition to the N Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> N bond of an azocarboxamide, generating a N-amino-N′-aryl urea derivative of a substituted aminoester. Treatment with a base forms an ester enolate which undergoes arylation by intramolecular migration of an aryl ring to the α-position of the ester. The product undergoes ring closure to a hydantoin, which may itself be deprotected and functionalised. Aryl migration is successful with rings of various electronic character and with esters bearing functionalised and unfunctionalised chains, and the products have features in common with several bioactive compounds.

Convergent synthesis of 13N-labelled Peptidic structures using aqueous [13N]NH3

Background

Nitrogen-13 has a 10-min half-life which places time constraints on the complexity of viable synthetic methods for its incorporation into PET imaging agents. In exploring ways to overcome this limitation, we have used the Ugi reaction to develop a rapid one-pot method for radiolabelling peptidic molecules using [¹³N]NH₃ as a synthetic precursor.

Methods

Carrier-added [¹³N]NH₃ (50 μL) was added to a solution of carboxylic acid, aldehyde, and isocyanide in 2,2,2-TFE (200 μL). The mixture was heated in a microwave synthesiser at 120 °C for 10 min. Reactions were analysed by radio-HPLC and radio-LCMS. Isolation of the target ¹³N–labelled peptidic Ugi compound was achieved via semi-preparative radio-HPLC as demonstrated for Ugi1.

Results

Radio-HPLC analysis of each reaction confirmed the formation of radioactive products co-eluting with their respective reference standards with radiochemical yields of the crude products ranging from 11% to 23%. Two cyclic γ-lactam structures were also achieved via intra-molecular reactions. Additional radioactive by-products observed in the radio-chromatogram were identified as ¹³N–labelled di-imines formed from the reaction of [¹³N]NH₃ with two isocyanide molecules. The desired ¹³N–labelled Ugi product was isolated using semi-preparative HPLC.

Conclusion

We have developed a one-pot method that opens up new routes to radiolabel complex, peptidic molecules with ¹³N using aqueous [¹³N]NH₃ as a synthetic precursor.

Electronic supplementary material

The online version of this article (10.1186/s41181-017-0035-7) contains supplementary material, which is available to authorized users.

Recent Advances in the Synthesis of Hydantoins: The State of the Art of a Valuable Scaffold

The review highlights the hydantoin syntheses presented from the point of view of the preparation methods. Novel synthetic routes to various hydantoin structures, the advances brought to the classical methods in the aim of producing more sustainable and environmentally friendly procedures for the preparation of these biomolecules, and a critical comparison of the different synthetic approaches developed in the last twelve years are also described. The review is composed of 95 schemes, 8 figures and 528 references for the last 12 years and includes the description of the hydantoin-based marketed drugs and clinical candidates.

Radioligands targeting P-glycoprotein and other drug efflux proteins at the blood-brain barrier

Brain penetration of radiopharmaceuticals or therapeutic drugs may be restricted by adenosine triphosphate-binding cassette (ABC) transporters, such as P-glycoprotein (Pgp), breast cancer resistance protein (BCRP), or the multidrug resistance-associated proteins. These transporters are expressed in the luminal membrane of brain capillary endothelial cells forming the blood-brain barrier (BBB), where they actively efflux a wide range of chemically unrelated compounds from the brain back into the blood. Most efforts to visualize ABC transporters at the BBB with positron emission tomography have concentrated on Pgp. Pgp imaging probes can be classified as radiolabeled substrates or inhibitors. The radiolabeled substrates (R)-[(11) C]verapamil and [(11) C]-N-desmethyl-loperamide have been successfully used to assess Pgp function at the BBB of animals and humans. Radiolabeled Pgp inhibitors, such as [(11) C]tariquidar, [(11) C]elacridar, or [(11) C]laniquidar, were developed to measure Pgp expression levels at the BBB, which has so far remained unsuccessful as these probes were unexpectedly recognized at tracer concentrations by Pgp and BCRP as substrates resulting in low brain uptake. Studies on positron emission tomography tracers for other ABC transporters than Pgp (BCRP and multidrug resistance-associated proteins) are still in their infancy. It is hoped that the experience gained with the imaging of Pgp will be successfully translated to the development of radiotracers to visualize other ABC transporters.

PET Tracers for Clinical Imaging of Breast Cancer

Molecular imaging of breast cancer has undoubtedly permitted a substantial development of the overall diagnostic accuracy of this malignancy in the last years. Accurate tumour staging, design of individually suited therapies, response evaluation, early detection of recurrence and distant lesions have also evolved in parallel with the development of novel molecular imaging approaches. In this context, positron emission tomography (PET) can be probably seen as the most interesting molecular imaging technology with straightforward clinical application for such purposes. Dozens of radiotracers for PET imaging of breast cancer have been tested in laboratory animals. However, in this review we shall focus mainly in the smaller group of PET radiopharmaceuticals that have lead through into the clinical setting. PET imaging can be used to target general metabolic phenomena related to tumoural transformation, including glucose metabolism and cell proliferation, but can also be directed to specific hormone receptors that are characteristic of the breast cancer cell. Many other receptors and transport molecules present in the tumour cells could also be of interest for imaging. Furthermore, molecules related with the tumour microenvironment, tumour induced angiogenesis or even hypoxia could also be used as molecular biomarkers for breast cancer imaging.