“…Products of the B‐series, characterized for possessing a 5'‐hydroxy group, are markedly more active than those of the A‐series, which contain a 5'‐methoxy group instead (Pitterna et al ., ; Wei et al ., ; Zhang et al ., ; Yoon et al ., ). However, it has been demonstrated that 1‐ and 2‐series products exert a similar activity against many parasites (Sunazuka et al ., ). In 1981, the antibiotic was refined by a reduction in the 22,23‐olefin of the most active avermectins, namely, B 1a and B 1b.…”