The bone resorption inhibitor minodronic acid hydrate was
approved and introduced last year in Japan, bringing the total
number of bis-phosphonates marketed for this indication to seven.
There are an estimated 10 million current and potential osteoporosis
sufferers in Japan, a number that is expected to continue
growing due to the country’s aging population. Minodronic acid is the first drug to show a significant effect in preventing bone fractures
as compared to placebo in a Japanese patient population.
Minodronic acid was co-developed by Astellas and Ono, who are
marketing the drug as Bonoteo and Recalbon, respectively.
Synthesis
Several syntheses of minodronic acid have been reported,a scalable preparation is described in the scheme. Commercially
available acid chloride 71 was first reduced with lithium
tritertbutoxy aluminum hydride to the aldehyde 72 at 80??C in
61% yield. Next, reaction of aldehyde 72 with TMSCl and triethylamine
generated the corresponding silyl enol ether, which was
then treated with bromine to give a-bromoaldehyde 73 in 62% yield. Condensation with 2-amino pyridine furnished imidazopyridine
74, which was hydrolyzed with HCl to acid 75 in 58% yield.
Reaction with H3PO3 at 120??C to provide minodronic acid hydrate
(XII) in 53% yield.
