We kick off season 2 with a bang, talking about complex molecule synthesis with John McIntosh and Nastaran Salehi. Cyclic dinucleotides (CDNs) are a total synthesis fan's dream with 10 stereocenters (including 2 at phosphorus) arranged around a 13 membered macrocycle formed by 2 non-canonical nucleosides. These endogenous secondary messenger molecules have attracted attention because of their activation of the immune system via the STING pathway. We go into all aspects of the innovative biocatalytic cascade that the team designed for their synthesis, including: 1) How a bald eagle cyclic guanosine-adenosine synthase (cGAS) was engineered to form the macrocycle; 2) How cGAS was leveraged by medicinal chemists to greatly accelerate drug discovery; 3) How the team strung together and optimized a 4-enzyme cascade to deliver a CDN directly from nucleotide building blocks.
Read the papers we discussed today here: 
A kinase-cGAS cascade to synthesize a therapeutic STING activator - Nature
New Mechanism for Cinchona Alkaloid-Catalysis Allows for an Efficient Thiophosphorylation Reaction - J. Am. Chem. Soc.
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