The Ascamycin has C2-chloroadenine as the base on C-1' which lacks the chlorine[1]. Ascamycin has a selective antibacterial activity against Xanthomonas species. When Ascamycin is dealanylated, Dealanylascamycin shows a broad antibacterial activity against various Gram-negative and Gram-positive bacteria. Xanthomonas citri is susceptible to Ascamycin by virtue of the Ascamycin-dealanylating enzyme on the cell surface[2].
References:
[1]. Isono K, et al. Ascamycin and dealanylascamycin, nucleoside antibiotics from Streptomyces sp. J Antibiot (Tokyo). 1984 Jun;37(6):670-2.
[2]. Osada H, rt al. Purification and characterization of ascamycin-hydrolysing aminopeptidase from Xanthomonas citri. Biochem J. 1986 Jan 15;233(2):459-63.
[3]. Zhao C, et al. Characterization of biosynthetic genes of ascamycin/dealanylascamycin featuring a 5'-O-sulfonamide moiety in Streptomyces sp. JCM9888. PLoS One. 2014 Dec 5;9(12):e114722.