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