Biogenetically-Inspired Total Synthesis of Epidithiodiketopiperazines and Related Alkaloids

Natural products chemistry has historically been the prime arena for the discovery of new chemical transformations and the fountain of insights into key biological processes. It remains a fervent incubator of progress in the fields of chemistry and biology and an exchange mediating the flow of ideas between these allied fields of science. It is with this ethos that our group has taken an interest in and pursued the synthesis of a complex family of natural products termed the dimeric epipolythiodiketopiperazine (ETP) alkaloids. We present here an Account of the highly complex target molecules to which we pegged our ambitions, our systematic and relentless efforts toward those goals, the chemistry we developed in their pursuit, and the insight we have gained for their translational potential as potent anticancer molecules.National Institute of General Medical Sciences (U.S.) (Grant GM089732)Amgen Inc

Labeling of monoclonal antibodies with rhenium-186 using the MAG3 chelate for radioimmunotherapy of cancer: A technical protocol

A detailed technical protocol is provided for reproducible and aseptical production of stable 186Re-monoclonal antibody conjugates. Labeled Mab E48 IgG and its F(ab')2 fragment which are promising candidates for radioimmunotherapy of squamous cell carcinoma of the head and neck were used for evaluation. S-benzoylmercaptoacetyltriglycine (S-benzoyl-MAG3) was used as a precursor. Rhenium-186-MAG3 was prepared via a unique solid-phase synthesis, after which known strategies for esterification and conjugation to Mab IgG/F(ab')2 were applied. The biodistribution of 186Re-E48 F(ab')2 in tumor-bearing nude mice was found to be comparable to that of analogously labeled 99mTc-E48 F(ab')2 or 131I-E48 F(ab')2, indicating that the intrinsic behavior of the antibody remains preserved when using this labeling technique. Radiolytic decomposition of 186Re-E48 IgG/F(ab')2 solutions of 10 mCi · ml-1 was effectively reduced by the antioxidant ascorbic acid. Upon increase of the Re-MAG3 molar amount, a conjugation of seven to eight Re-MAG3 molecules per Mab molecule was generally the maximum ratio that could chemically be obtained. Such a ratio did not impair the immunoreactivity or alter the in vivo biodistribution characteristics of the immunoconjugate, making this labeling procedure suitable for general clinical application

Fast and reliable generation of [18F]triflyl fluoride, a gaseous [18F]fluoride source

A novel strategy for the production of reactive [18F]fluoride has been developed, omitting time consuming azeotropic drying procedures. Gaseous [18F]triflyl fluoride is formed instantaneously at room temperature from hydrated [18F]fluoride, followed by distillation in less than 5 minutes into a dry aprotic solvent, in which dry [18F]fluoride is released in presence of base with >90% radiochemical yield. The reactivity of the [18F]fluoride has been confirmed by reaction with several model compounds and by the synthesis of the PET tracers [18F]fluoroestradiol ([18F]FES) and O-2-[18F]fluoroethyl-l-tyrosine ([18F]FET), providing good isolated radiochemical yields and molar activities of up to 123 GBq μmol−1

Synthesis and biodistribution of [11C]R107474, a new radiolabeled α2-adrenoceptor antagonist

R107474, 2-methyl-3-[2-(1,2,3,4-tetrahydrobenzo[4,5]furo[3,2-c]pyridin-2-yl)ethyl]-4H-pyrido[1,2-a]pyrimidin-4-one, was investigated using in vitro and in vivo receptor assays and proved to be a potent and relatively selective α2-adrenoceptor antagonist. Performed assays in vitro were inhibition of binding to a large number of neurotransmitter receptor sites, drug receptor binding sites, ion channel binding sites, peptide receptor binding sites, and the monoamine transporters in membrane preparations of brain tissue or of cells expressing the cloned human receptors. The compound has subnanomolar affinity for hα2A- and hα2C-adrenoceptors (Ki = 0.13 and 0.15 nM, respectively) and showed nanomolar affinity for the hα2B-adrenoceptors and 5-hydroxytryptamine7 (h5-HT7) receptors (Ki = 1 and 5 nM, respectively). R107474 interacted weakly (Ki values ranging between 81 and 920 nM) with dopamine-hD2L, -hD3 and -hD4, h5-HT1D-, h5-HT1F-, h5-HT2A-, h5-HT2C-, and h5-HT5A receptors. The compound, tested up to 10 μM, interacted only at micromolar concentrations or not at all with any of the other receptor or transporter binding sites tested in this study. In vivo α2A- and α2C-adrenoceptor occupancy was measured by ex vivo autoradiography 1 h after subcutaneous (sc) administration of R107474. It was found that R107474 occupies the α2A- and α2C-adrenoceptors with an ED50 (95% confidence limits) of 0.014 mg/kg sc (0.009-0.019) and 0.026 mg/kg sc (0.022-0.030), respectively. Radiolabeled 2-methyl-3-[2-([1-11C]-1,2,3,4-tetrahydrobenzo[4,5]furo[3,2-c]pyridin-2-yl)ethyl]-4H-pyrido[1,2-a]pyrimidin-4-one ([11C]R107474) was prepared and evaluated as a potential positron emission tomography (PET) ligand for studying central α2-adrenoceptors. [11C]R107474 was obtained via a Pictet-Spengler reaction with [11C]formaldehyde in 33 ± 4% overall decay-corrected radiochemical yield. The total synthesis time was 55 min and the specific activity was 24-28 GBq/μmol. The biodistribution of [11C]R107474 in rats revealed that the uptake of [11C]R107474 after in vivo intravenous administration is very rapid; in most tissues (including the brain) it reaches maximum concentration at 5 min after tracer injection. In agreement with the known distribution of α2-adrenoceptors in the brain, highest uptake of radioactivity was observed in septum (3.54 ± 0.52 ID/g, 5 min pi) and entorhinal cortex (1.57 ± 0.10 ID/g, 5 min pi). Tissue/cerebellum concentration ratios for septum (5.38 ± 0.45, 30 min pi) and entorhinal cortex (3.43 ± 0.24, 30 min pi) increased with time due to rapid uptake followed by a slow washout. In vivo blocking experiments using the non-selective α2-adrenoceptor antagonist mirtazapine demonstrated specific inhibition of [11C]R107474 binding in selective brain areas. The receptor binding profile of mirtazapine is reported and the selectivity of inhibition of binding is discussed. These results suggest that [11C]R107474 deserves further investigation as a potential radioligand for studying α2-adrenoceptors using PET