Radioiodination of 7-methoxy- and 6,7-dimethoxy-4-bromomethylcoumarins

✍ Scribed by Janina Baranowska-Kortylewicz; Zbigniew P. Kortylewicz

• Book ID: 102375791
• Publisher: John Wiley and Sons
• Year: 1991
• Tongue: French
• Weight: 278 KB
• Volume: 29
• Category: Article
• ISSN: 0022-2135
• DOI: 10.1002/jlcr.2580291206

✦ Synopsis

Abstract

Two coumarins, 4‐bromomethyl‐6,7‐dimethoxy‐2‐oxo‐2__H__‐benzopyran (1) and 4‐bromomethyl‐7‐methoxy‐2‐oxo‐2__H__‐benzopyran (3), were radioiodinated using trifluoroacetyl hypoiodite. The dimethoxy derivative 1 gave only a single regioisomer 3‐[^125^I]iodo‐4‐bromo‐methyl‐6,7‐dimethoxy‐2‐oxo‐2__H__‐benzopyran (2). The average yield for no‐carrier‐added preparations of 2 was 30%. ^125/127^I‐2 and ^127^I‐2 were produced in over 50% yield. In no‐carrier‐added syntheses 7‐methoxy‐coumarin 3 gave 3‐[^125^I]iodo‐4‐bromomethyl‐7‐methoxy‐2‐oxo‐2__H__‐benzopyran(5) as the major product (30%) accompanied by a small amount (3–7%) of the 6‐[^125^I]iodo‐analog 4. When an equimolar amount of iodide was used (i.e. carrier‐added syntheses) 4 and 5 were produced in over 20% yield each. Under these conditions the 8‐iodo‐regioisomer was not formed from either 1 or 3 possibly as the result of steric effects. Sonication greatly accelerated rates of radioiodination reducing the time required to achieve quantitative substitution of ^127^I from about 4 h to 20 min.