Tigecycline Impurity 1;Tigecycline USP Related Compound A;(3S,4R)-7-(2-(tert-butylamino)acetamido)-;Tigecycline impurity;Tigecycline USP Impurity A;Tigecycline Open Ring Impurity;Tigecycline Open Ring Impurity 1;Tigecycline EP Impurity D(Tigecycline open ring)