Analysing these routes may unveil useful sub-routes. As shown in Fig. , a shorter sub-route from PPP to S-Zanubrutinib was found, which also avoided using organochlorine (acryloyl chloride) as a hazardous intermediate. Although development of chromatographic separation could be a challenge, this result may encourage researchers to devote efforts on this path. Other notable sub-routes for the synthesis of key intermediates (APPCN and TBPPC) are summarized in Figs. and. These results may help to design shorter and safer routes. Many reactions identified in this search are not typically found in the routes to S-Zanubrutinib (e.g., a bio-synthesis 9010270 in Fig. ). Although more than 5,000 routes were found in the first round of search, all routes started from a group of only 50 feedstocks, among which not many renewable feedstocks were identified, suggesting the searching was not deep-enough to reach to renewable feedstocks. Therefore, 4-step retrosynthesis searches were conducted from two key feedstocks, i.e., 4PA and BPA. Some encouraging routes are shown in Figs. 9 and 10. The small reaction network in Fig. suggested that all carbons of 4PA can be derived from lignin and CO2. For the synthesis of BPA, platform molecules from cellulose, e.g., D-glucose, D-sorbitol, furfural alcohol, may be employed as suitable building blocks, see Fig. . Many reactions were conducted in environmentally benign media such as water, ionic liquids, using bio-synthesis or solvent free. A promising route starting from a hub molecule (pyridine) was also found. This route contains many attractive features: incorporation of CO2 via an electrochemical reaction, incorporation of salt of formic acid via heterogeneous catalysis, free of hazardous reagents, high yield of each reaction step. To sum up this section, we have achieved the following with the help of "search synthesis routes" routine of CDI-CASP: