Research Projects

Turonicin A is a linear polyene polyketide natural product isolated from Streptomyces sp. MST-123921 bacterial strain collected from soil sample of banks of Turon river in Australia in 2023 by Piggott and co-workers. The compound showed very significant antifungal activity against Candida albicans and Saccharomyces cerevisiae with MIC values 0.0031 μg/mL and 0.0008 μg/mL, respectively as well as good antibacterial activity against Bacillus subtilis and Staphylococcus aureus with MIC values 0.097 μg/mL and 0.39 μg/mL respectively. Structurally, turonicin A is a 59-carbon linear polyene polyketide where one end terminated with a carboxylic acid group and the other extremity is substituted with a guanidine moiety. The amphoteric linear polyene architecture of the molecule consists of fifteen stereogenic centers bearing twelve hydroxy and three methyl substituents. In addition, the polyketide framework embedded with a tetraene, and a pentaene chromophores along with multiple isolated double bonds. These structural features in overall represented the natural product as quite complex and made synthetically extremely challenging. Linearmycins A-C, mediomycins A-B, clethramycin and tetrafibricin are structurally related linear polyketide natural products isolated earlier from various sources. However, there is no report on their total syntheses except some of the fragment synthesis of tetrafibricin. We have proposed here a logical synthetic strategy for total synthesis of turonicin A applying Julia-Kocienski olefination, Stille cross coupling, Suzuki cross coupling, HWE olefination, boron mediated anti aldol reaction. The chemistry proposed here would be executed in Indian Association for the Cultivation of Science, Kolkata at Prof. Rajib K. Goswami’s laboratory which is one of the pioneering laboratories of such chemistry in India. Finally, the Structure Activity Relationship (SAR) of the proposed turonicin A will be explored to understand the molecular basis of this natural product against different biological aspects.