were observed, respectively. Compared to 16c, a slightly higher enzymatic susceptibility was observed for 15c, as indicated by 50.7% and 59.1% of 15c and 16c, respectively, remaining undegraded after 6 h incubation. After 24 h incubation, 31.2% and 37.7% of 15c and 16c, respectively, remain undegraded. The data suggested that 15c and 16c demonstrate good stability in human plasma with a half-life (t1/2) of 6 h and 8 h, respectively.