| CPC C07F 5/027 (2013.01) [C07B 59/004 (2013.01); C07C 229/34 (2013.01); C07C 249/02 (2013.01)] | 20 Claims | 

| 
               1. An intermediate I of the structure 
              ![]() where R1 represents boric acid groups or substituents that is hydrolyzable to boric acid groups; 
                R2 represents boric acid groups or substituents that is hydrolyzable to boric acid groups; 
                R3 represents hydrogen, an amino-protecting group, or an imino group combined with an amino group for protecting the amino group; 
                R4 represents hydrogen, an amino-protecting group, or an imino group combined with an amino group for protecting the amino group; and 
                R5 represents hydrogen or a carboxyl-protecting group. 
               |