Macrolide antibiotics, such as tylosin (Fig. 1), a 16-membered macrolide antibiotic produced by Streptomyces fradiae, consist of polyketide lactones substituted with 6-deoxysugars and are widely used in veterinary and human medicine. The number, nature and relative distribution of the sugar moieties determine the pharmacokinetic properties of the macrolide antibiotics [1]. Biosynthesis of tylosin involves the attachment of three deoxyhexose sugars (d-mycaminose, 6-deoxy-d-allose and l-mycarose) to a 16-atom lactone (protylonolide, synonym tylactone) [2]. Addition of the sugars proceeds in a preferred but not mandatory order (although mycaminose is always added first) [3] (Fig. 1). Concurrently with glycosylation, the polyketide lactone is also hydroxylated at C-20 and C-23, the latter being the site a deoxyallose is subsequently added [4]. Six genes were known to be involved in the biosynthesis of l-mycarose in S. fradiae. Deletion of tylCV from the chromosome of S. fradiae, which encodes mycarosyltransferase, results in the accumulation of desmycosin [5], the direct precursor of semisynthetic macrolide antibiotic—tilmicosin (Fig. 1). Tilmicosin is an important drug developed exclusively for veterinary health, which is synthesized by the introduction of a 3,5-dimethylpiperidine moiety at C-20 of desmycosin via reductive amination [6]. As a result of long half-life, tilmicosin is effective for the treatment of respiratory disease in cattle.