An Abundant New Saponin-Polybromophenol Antibiotic (CU1) from Cassia fistula Bark Against Multi-Drug Resistant Bacteria Targeting RNA Polymerase

Spread of multidrug-resistant infections is a threat to human race and need for new drug development is great. Bark ethanol extract of Cassia fistula inhibited MDR bacteria isolated from Ganga River water, human and animal. On TLC, a gray colour major band ran fast (CU1; 6.6% of bark and ~30% of crude extract) which quickly purified on HPLC C18 column at 3 min. Chemical assays suggested a triterpene linked to polyphenol known as saponin. CHN Elements analysis (35.9% C; 5.5% H) did not identified nitrogen suggesting a polyphenol or glycoside. VU-Vis spectra gave high peak at below 200nm with a secondary peak at 275nm with minor hinge at 578nm indicating a fused ring with bromo-polyphenol. CU1 Mass (897 Daltons) with fragments of 515, 325, 269, 180 daltons and six halogen substitutions reflected by 82 molecular mass of DBr deviate six larger fragments. FT-IR suggested broad band at 3500-3000 cm-1 for -OH where as two strong peaks at 1552cm-1 for aromatic C=C and 1408cm-1 for phenol. Proton-NMR confirmed polymeric phenol at {delta} 4.86-4.91 ppm and tetratet at {delta}3.57-3.618 ppm with phenolic bromo-substituents. Carbon-NMR identified a strong peak at {delta}=23.7ppm for many C-Br and at 165ppm for a polybenzoid compound. CU1 inhibited the RNA Polymerase of E. coli (IC50=23g/ml) and M. tuberculosis (IC50=34g/ml) but not DNA polymerase. Gel shift assays demonstrated that CU1 drug interacted with enzyme and inhibited its binding to open promoter complex. Thus, CU1 phyto-chemical is an alternative safer and low cost drug against MDR-TB as well as other MDR pathogens.