Synthesis and Evaluation of Paromomycin Derivatives Modified at C(4′)

The 2‐amino‐2‐deoxy‐α‐D ‐glucopyranosyl moiety (ring I) of paromomycin was replaced by a 2,4‐diamino‐2,4‐dideoxy‐α‐D ‐glucopyranosyl, 2,4‐diamino‐2,4‐dideoxy‐α‐D ‐galactopyranosyl, 2‐amino‐2‐deoxy‐α‐D ‐galactopyranosyl, or 3,4,5‐trideoxy‐4‐aza‐α‐D ‐erythro‐heptoseptanosyl moiety to investigate the effect of the substituent at C(4′) on the interaction with ribosomal RNA. The triflate 6 was prepared from the key intermediate pentaazido 3′,6′‐dibenzyl ether 5 , and the hexosulose 10 was obtained by oxidation of 5 with Dess–Martin's periodinane. Stereoselective reduction of 10 with NaBH₄ gave the alcohol 11 that was transformed into the triflate 12 . The epimeric hexaazides 7 and 13 were obtained by treating the triflates 6 and 12 , respectively, with tetrabutylammonium azide. Periodate cleavage of glycol 2 yielded the dialdehyde 24 that was reductively aminated with aniline and benzylamine to give the 3,4,5‐trideoxy‐4‐aza‐α‐D ‐erythro‐heptoseptanosides 25 and 26 , respectively. Standard azide reduction and debenzylation yielded 9 (2,4‐diamino‐2,4‐dideoxy‐α‐D ‐galactopyranosyl ring I), 13 (2‐amino‐2‐deoxy‐α‐D ‐galactopyranosyl ring I), 17 (2,4‐diamino‐2,4‐dideoxy‐α‐D ‐glucopyranosyl ring I), and 27 and 28 (3,4,5‐trideoxy‐4‐aza‐α‐D ‐erythro‐heptoseptanosyl ring I). The derivatives 9 and 13 possessing a D ‐galacto‐configured ring I were less active than the corresponding D ‐gluco‐analogues 17 and paromomycin ( 1 ), respectively. The C(4′)‐aminodeoxy derivative 17 (D ‐gluco ring I) and the known 4′‐deoxyparomomycin ( 23 ), prepared by a new route, displayed slightly lower antibacterial activities than paromomycin ( 1 ). Cell‐wall permeability is not responsible for the unexpectedly low activity for 17 , as shown by cell‐free translation assays. The results evidence that the orientation of the substituent at C(4′) is more important than its nature for drug binding and activity.