合成路线1

Condensation of amine (I) with N,N’-di-Boc-thiourea (II) using HgCl2 and Et3N in DMF (1) or with di-Boc-amidinopyrazole (III) in THF gives the protected guanidine derivative (IV), which by deacetylation with methanolic sodium methoxide followed by saponification of the deacylated methyl pyranosoate (V) leads to the carboxylic acid (VI). Alternatively, acid (VI) is prepared by direct hydrolysis of compound (IV) by means of aqueous NaOH or K2CO3 in H2O/MeOH. After conversion of acid (VI) to the corresponding benzhydryl ester (VII) by treatment with diphenyldiazomethane and BF3·Et2O, selective acylation of the primary hydroxyl group with octanoyl chloride (VIII) and Et3N in CH2Cl2 yields the 9-octanoate ester (IX) (1). Finally, compound (IX) is deprotected by removal of N-Boc and O-benzhydryl protecting groups by treatment with trifluoroacetic acid in CH2Cl2, followed by basification of the obtained TFA salt with NaHCO3 (2-8). Scheme 1.
Alternatively, reaction of the 4-amino-5,6-dihydropyran derivative (X) with di-Boc-amidinopyrazole (III) provides the corresponding 4-guanidinodihydropyran, which is hydrolyzed with K2CO3 in MeOH/H2O to give carboxylic acid (VI). In an alternative strategy, carboxylic acid (VI) is prepared by hydrolysis of the 4-amino-5,6-dihydropyrancarboxylate ester (X) with NaOH followed by reaction with the amidinopyrazole derivative (III). Deprotection of di-Boc intermediate (VI) by stirring at 80 °C in MeOH gives laninamivir (XI), which is finally selectively acylated with trimethyl orthooctanoate (XII) in the presence of methanolic HCl. Laninamivir (XI) can also be obtained by hydrolysis of intermediate (X) with NaOH followed by reaction of the resulting free amine (XIII) with pyrazole-1-carboxamidine HCl (XIV) or, alternatively, by treatment of 4-amino-5,6-dihydropyran (X) with pyrazole-1-carboxamidine HCl (XIV), and then hydrolysis of the methyl ester with K2CO3 in MeOH (3). Scheme 1.