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Capsanthin, a characteristic red carotenoid found in the fruits of red pepper (Capsicum annuum), is widely consumed as a food and a functional coloring additive. An enzyme catalyzing capsanthin synthesis was identified as capsanthin/capsorubin synthase (CCS) in the 1990s, but no microbial production of capsanthin has been reported. We report here the first successful attempt to biosynthesize capsanthin in Escherichia coli by carotenoid-pathway engineering. Our initial attempt to coexpress eight enzyme genes required for capsanthin biosynthesis did not detect the desired product. The dual activity of CCS as a lycopene β-cyclase as well as a capsanthin/capsorubin synthase likely complicated the task. We demonstrated that a particularly high expression level of the CCS gene and the minimization of byproducts by regulating the seven upstream carotenogenic genes were crucial for capsanthin formation in E. coli. Our results provide a platform for further study of CCS activity and capsanthin production in microorganisms.

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Focused libraries of enamine derivatives with a nonacidic, nonelectrophilic core structure were screened for inhibitors of dual-specificity protein phosphatases, and an o-hydroxybenzyl derivative RE44 (10d) was identified as a selective inhibitor of CDC25A/B. This inhibitor induced cell-cycle arrest of tsFT210 cells at the G2/M phase and inhibited dephosphorylation of the CDC25B substrate CDK1. Unlike most quinone-based inhibitors, 10d does not generate reactive oxygen species.