| 摘要 |
Cpds. of formula (I): (where R = a carboxyprotecting gp. Specifically methyl, T-butyl, 2,2,2-tricloroethyl, benzyl, p-methoxybenzyl, p-nitrobenzyl or phenacyl) can be converted to 7-amino-3-desacetoxycephalosporanic acid (7-ADCA) by (i) reducing (Zn-acetic acid) to the chloroacetylamino cpd. then reacting with thiourea in aq. medium to give 7-ADCA (this process is used when R = trichloroethyl and this gp. is replaced by H during the redn), (ii) when R is not = trichloroethyl, R is first converted to H (acid hydrolysis or hydrogenolysis or alkali thiophenoxide) then Cl3CCO is replaced by H by borohydride redn. (iii) when R is not = trichloroethyl or phenacyl. (I) is reduced (borohydride) to the 7-amino cpd. and this is then deprotected at the 4 posn. by hydrolysis or hydrogenolysis. 7-ADCA is a starting matl. for cephalexin and other semi-synthetic cephalosporin antibiotics. By this process it is produced inexpensively from a readily available cpd. such as penicilling G. |
