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. 2020 Jan 27;128(1):017014. doi: 10.1289/EHP5053

Figure 3.

Figures 3A, 3B, and 3C are chemical reactions. In 3A, 7DHC leads to 7DHC-PTAD through PTAD. In 3B, Des leads to Des-PTAD through PTAD. In 3C, 8DHC leads to Ene through PTAD, and Ene leads to 5, 7, 9 triene (which also leads to 5, 7, 9 PTAD) plus 5, 9, 14 triene (which also leads to 5, 9, 14 MeOH adduct).

Proposed mechanism for the reaction of (A) 7-dehydrocholesterol, (B) desmosterol (or lanosterol), and (C) 8-dehydrocholesterol with PTAD. 7-DHC undergoes a Diels-Alder reaction, whereas Des and Lan undergo an ene reaction on the tail olefin. For 8-DHC, the Diels-Alder and MeOH adducts are the major products formed through a series of ene, elimination, and Diels-Alder reactions.