Synthesis

In 2011, Collier and co-workers published a communication describing both the original synthesis of bilastine and an improved route which was amenable to gram-scale production. Collier’s second generation route, shown below, relies upon a convergent approach involving the union of piperidinyl benzimidazole 49 with fully functionalized phenethyl electrophile 48.Coupling the commercially available bromophenyl acetate 44 with cyclic trioxatriborinane 45 under conventional Suzuki conditions furnished styrene 46 in good yield. Alternatively, this vinylation reaction was also performed under Stille conditions with tributyl vinyl stannane in 83% yield. Hydroboration–oxidation of 46 delivered phenethyl alcohol 47 which was then immediately mesylated under basic conditions in toluene to produce adduct 48. This sulfonate was then reacted with piperidine 49 (whose preparation is described in Scheme 7) followed by saponification of the resulting ester 50 to arrive at bilastene (VI) in 26% overall yield from 44. For the preparation of bilastine piperidine 49, commercially available piperidine 51 was first protected as the Boc-carbamate 52 prior to alkylation of the benzimidazole nitrogen atom with 1-chloro-2-ethoxyethane 53, providing compound 54. The Boc group of 54 was removed under acidic conditions to give fragment 49. This sequence produced the desired piperidine component in 86% overall yield from 51.

Drug interactions

Potentially hazardous interactions with other drugs Antivirals: concentration possibly increased by ritonavir. Grapefruit juice: concentration of bilastine reduced.

Metabolism

Not significantly metabolised. Almost 95% of the administered dose was recovered in urine (28.3%) and faeces (66.5%) as unchanged bilastine

Brand name

Bilaxten