Sansanmycins are members of uridyl-peptide antibiotics (UPAs) isolated from Streptomyces sp. SS (CPCC 200442) in our previous researches.1, 2, 3, 4 More than 10 related compounds have been identified, which share a common structure with pacidamycin,5 mureidomycin6 and napsamycin.7 They are composed of a 3′-deoxyuridyl attached via an unusual exocyclic enamide to a penta- or tetra-pseudopeptide backbone assembled by nonribosomal peptide synthetases.8 The uridyl-peptide antibiotics represent a family of promising leading compounds that they target a clinic unexplored target, MraY translocase, to inhibit the bacterial cell-wall synthesis and show good activity against highly refractory pathogens Pseudomonas aeruginosa and Mycobacterium tuberculosis.9

[4-Me–Phe]-sansanmycin H (1) is a white powder (melting point 204–206 °C) with a molecular weight of 838, two mass units smaller than that of sansanmycin H, which hinted at the replacement of the hydroxyl group in sansanmycin H with a methyl group in compound 1. Furthermore, the daughter ion m/z 658, corresponding to the loss of C-terminal amino acid of sansanmycin H, also appeared as base peak in the electrospray ionization mass/mass spectrum of compound 1, which indicated the 4-methylphenylalanine was incorporated into the C-terminus of 1. Compared with the 1H NMR spectrum of sansanmycin H,1 that of 1 showed an extra methyl proton signal at δ 2.29 (s, Ar−CH3), which further confirmed the above hypothesis. Interpretation of the 2D NMR and ESIMS/MS data (Table 1 and Figure 2) also confirmed this expected structure.

Table 1 1H NMR (600 MHz) and 13C NMR (125 MHz) data for [4-R–Phe]-sansanmycin H (1–4)
Full size table

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