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In this study, a novel preparation method of theaflavin (TF) has been established. Our findings indicated that the formation of TF was significantly enhanced by using an ice bath (2–3°C). Additionally, increasing the ratio of (−)‐epigallocatechin (EGC) under the ice bath could further improve its yield. This approach prevented the appearance of a dark solution within 3 h, effectively protecting TF from oxidation. Our study on the generation mechanism of TF suggested that EGC‐quinone I (EGC‐Q‐I) with two carbanions could potentially serve as one of synthons based on the retrosynthetic analysis of the bicyclo[3.2.1]octane‐type intermediate. Subsequently, quantum mechanical calculations further supported this hypothesis. Practical Application: In this study, we have developed a novel method for the synthesis of theaflavin (TF), demonstrating that the use of ice bath significantly enhanced its yield. Increasing the ratio of (−)‐epigallocatechin (EGC) under the ice bath further improved TF yields and prevented darkening of the solution for at least 3 h, thereby protecting TF from oxidation. Our study suggested that EGC‐quinone I is a potential synthon based on the retrosynthetic analysis of the bicyclo[3.2.1]octane‐type intermediate (BOI). This hypothesis is supported by QM calculations. [ABSTRACT FROM AUTHOR]

Summary: Theaflavin‐3,3′‐digallate (TFDG) is the main product formed by oxidative condensation between (−)‐Epigallocatechin‐3‐gallate (EGCG) and (−)‐Epicatechin‐3‐gallate (ECG). Some sub‐products, such as homo‐ and hetero‐oligomers of EGCG and ECG, are also produced simultaneously, which significantly decreases the yield of TFDG. In general, the optimum temperature for TFDG synthesis is 20 °C below which can reduce its generation resulting in the coexistence of a large amount of unreacted substrates (ECG and EGCG). Therefore, a higher possibility of increasing the formation of TFDG could be achieved if a suitable synthetic method can be developed at a low temperature. Our results showed that simultaneous dropwise addition of both EGCG and ECG could markedly enhance the content of TFDG at ice bath. Using such technique, the production of TFDG increased by 47.60% as compared to the group synthesised under the optimum temperature. The absorbance of TFDG at 278 nm is 2.36 times higher than that of ECG with equimolar concentration. Therefore, a rapid, simple and accurate calculation method of TFDG yield was developed via the spectral correlation. Based on the counting method, the yield of TFDG was 30.58% by using the novel synthetic method of TFDG. [ABSTRACT FROM AUTHOR]