Significance: Colorectal cancer (CRC) remains an unmet need and is a significant challenge to the healthcare system as one of the leading forms of cancer in the United States, affecting an estimated 136,830 people and causing an estimated 50,310 deaths in 2014. Estimates of base case for the medical care costs for colorectal cancer in 2010 were $14.14 billion and it is projected to increase to $17.41 billion by 2020. Largazole is a differentiated novel class I selective histone deacetylase (HDAC) inhibitor derived from a marine cyanobacterium, that shows selective anticancer activity, both in vitro and in vivo. Hypothesis: Our overall hypothesis is that largazole is an effective novel therapeutic agent for metastatic and/or refractory CRC and potentially other refractory solid tumors. To support clinical development, we first need to synthesize sufficient quantities of largazole, and develop a more robust method for large-scale synthesis, amenable to subsequent manufacture. Completion of this Phase I SBIR goal will allow us to focus on future preclinical studies to test this hypothesis in Phase II. Preliminary Data: The NCI60 screen showed largazole to be highly active against colon cancer cells, and it modulated gene expression, induced cell cycle inhibitors such as p21 and downregulated cancer-associated receptor tyrosine kinases (RTKs), resulting in concentration-dependent cell cycle arrest and apoptosis. Largazole, was efficacious in HCT116 colon tumor xenograft mouse model, retarding tumor growth without acute toxicity at intraperitoneal doses up to 50 mg/kg. In an in vivo breast cancer model of highly invasive MDA-MB-231 cells (representing triple negative breast cancer), largazole, combined with dexamethasone, reduced the invasiveness of cancer cells by mediating cell-cell contacts, i.e. prevented cell movement and metastasis. In addition to its in vivo anticancer and anti-invasive properties, largazole showed bone-forming activity in mouse and rabbit in vivo models and it reduced CCl4-induced liver fibrosis. Specific Aims: Largazole preclinical evaluations, formulation development and subsequent clinical trials, requires a scalable synthetic method to produce larger amounts of material. In Aim #1, we will focus on the synthesis of some of the key building blocks of largazole. Specifically, we will evaluate the synthesis of thioacid, thioester, (R)-2-methyl cysteine, Boc-protected 2-aminomethyl-4-cyano-thiazole and alcohol. In Aim #2, we will conduct process chemistry research to improve the yields of the two final steps of largazole synthesis focused on the macrocyclization and cross-metathesis reactions. The identity and purity of all compounds will be verified by NMR and mass spectrometry. We expect that we will be able to produce adequate quantities of key building blocks and improve the yields of the last two steps of synthesis to approximately 80%, allowing a significant improvement in the yield of largazole through this novel, scalable synthetic method to provide material for preclinical studies (to be pursued in a Phase II proposal) and eventual clinical development of largazole.