302 Chapter 9 hydroxylation If a hydroxyl group is introduced into position C-19 then complete breakdown of the examples shown in Figure 9.3, the incubation of 19-hydroxysterols with Nocardia restricTus ATCC 14887 or Nocardia sp ATCC 19170 leads to the production of estrone. In these cases, you will notice that ring a has become modified but the ring structure is not broken. The yields of estrone using these substrates and organisms are of the order of HOCH H 2- CH3 d Figure 9. 3 The figure shows the degradation of the side chain of sterols which have substitutions at C-19. Removal of the C-19 methyl group(eg 19 norcholesta-1, 3, 5 (10) riene-3-ol)also prevents ring breakdown. Note, however, hydroxylation of C-19 does not prevent all ring modifications a:19-hydroxycholesterone, b: 19-hydroxysitosterone, c: 3B-acetoxy-19-hydroxy-5-cholestene Other modifications which restrict ring cleavage are the formation of 6B, 19-oxido derivatives and 3a, 5a cyclo-derivatives. The structures of some of these are given in302 Chapter 9 If a hydroxyl group is introduced into position C-19 then complete breakdown of the ring structure is prevented, although it may be sub- to some modification. In the exampl? shown in Figure 9.3, the incubation of 19-hydroxysterols with Nocardia restn'ctus ATCC 14887 or Nocardia sp ATCC 19170 leads to the production of estrone. In these cases, you will notice that ring A has become modified but the ring structure is not broken. The yields of estrone using these substrates and organisms are of the order of 30%. hydroxylation ate19 ~~ ~~~~ ~~ Figure 9.3 The figure shows the degradation of the side chain of sterols which have substitutions at C-19. Removal of the C-19 methyl group (eg 19 norcholesta-l13,5 (1 0) triene-3-01) also prevents ring breakdown. Note, however, hydroxylation of C-19 does not prevent all ring modifications. a: 19-hydroxychoIesterone, b: 1 9-hydroxyslosterone, c: 3p-acetoxy-l9-hydroxy-5cholestene, d: estrone. Other modifications which restrict ring cleavage are the formation of 6fi,19-oxido derivatives and 3a, 5a cyclo-derivatives. The structures of some of these are given in Figure 9.4