An efficient and practical synthesis of [2-11C]indole via superfast nucleophilic [11C]cyanation and RANEY® Nickel catalyzed reductive cyclization
- Brookhaven National Lab. (BNL), Upton, NY (United States). Biological, Environmental & Climate Sciences Department
- Brookhaven National Lab. (BNL), Upton, NY (United States). Biological, Environmental & Climate Sciences Department; Johannes Gutenberg Univ., Mainz (Germany). Institut fur Kernchemie
- Brookhaven National Lab. (BNL), Upton, NY (United States). Biological, Environmental & Climate Sciences Department; Massachusetts General Hospital, Harvard Medical School, Charlestown, MA (United States)
- Massachusetts General Hospital, Harvard Medical School, Charlestown, MA (United States)
We developed a rapid method for the synthesis of carbon-11 radiolabeled indole using a sub-nanomolar quantity of no-carrier-added [11C]cyanide as radio-precursor. Based upon a reported synthesis of 2-(2-nitrophenyl)acetonitrile (2), a highly reactive substrate 2-nitrobenzyl bromide (1) was evaluated for nucleophilic [11C]cyanation. Additionally, related reaction conditions were explored with the goal of obtaining of highly reactive 2-(2-nitrophenyl)-[1-11C]acetonitrile ([11C]-2) while inhibiting its rapid conversion to 2,3-bis(2-nitrophenyl)-[1-11C]propanenitrile ([11C]-3). Next, a Raney Nickel catalyzed reductive cyclization method was utilized for synthesizing the desired [2-11C]indole with hydrazinium monoformate as the active reducing agent. Extensive and iterative screening of basicity, temperature and stoichiometry was required to overcome the large stoichiometry bias that favored 2-nitrobenzylbromide (1) over [11C]cyanide, which both caused further alkylation of the desired nitrile and poisoned the Raney Nickel catalyst. The result is an efficient two-step, streamlined method to reliably synthesize [2-11C]indole with an entire radiochemical yield of 21 ± 2.2% (n = 5, ranging from 18 – 24%). The radiochemical purity of the final product was > 98% and specific activity was 176 ± 24.8 GBq/μmol (n = 5, ranging from 141 – 204 GBq/μmol). The total radiosynthesis time including product purification by semi-preparative HPLC was 50 – 55 min from end of cyclotron bombardment.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Biological and Environmental Research (BER)
- Grant/Contract Number:
- SC0012704
- OSTI ID:
- 1239796
- Report Number(s):
- BNL-111763-2016-JA; OBCRAK
- Journal Information:
- Organic and Biomolecular Chemistry, Vol. 13, Issue 46; ISSN 1477-0520
- Publisher:
- Royal Society of ChemistryCopyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
Synthesis of
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journal | April 2018 |
11 C-Labeling: Intracyclic Incorporation of Carbon-11 into Heterocycles: 11 C-Labeling: Intracyclic Incorporation of Carbon-11 into Heterocycles
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journal | October 2019 |
New trends and applications in cyanation isotope chemistry
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journal | May 2018 |
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