Novel tetracycline SBR-22 is a functional moiety deviation and bioactive against multidrug resistant strains

Abstract A new tetracycline analogue SBR-22 was isolated using bioactivity guided screening of the Streptomyces psammoticus 125-vr, from sea residues of the Visakhapatnam coast of South India. Based on spectral data, the name and structure of the antibiotic SBR-22 were identified as 1,5-dihydroxy- 5-methyl- 7- (N,N-dimethyl) amino- 6,8,11,12- tetraoxo- 7,9,10 –hexahydro- naphthacene. Unlike the standard oxytetracycline pharmacophore (OTP) at C2 and C1 positions, the SBR-22 molecule lacked (C9) -carbamido and (C10) keto functional groups. Furthermore, the oxidation of the B-ring, caused by the presence of two keto carbonyls at opposite positions, resulted in a Quinone ring system, making it an effective antibiotic. Unlike the OTP molecule, four prime functional groups in the A and B-rings were either absent or altered in this native novel molecule SBR-22, which successfully retained its bioactivity against inhibit multidrug resistant strains of bacteria. Hence, this new analogue SBR-22 is effective (64 µg/ml -1 minimum inhibitory concentration (MIC 90 )) against methicillin resistant Gram-positive bacteria Staphylococcus aureus and human pathogenic fungi Aspergillus wentii and A. niger (42 µg/ml -1 of MIC 90 ). Interestingly, it can also inhibit MDRS of Pseudomonas aeruginosa and yeast Candida albicans (MIC 90 of 128 µg/ml -1 ), respectively.