Moxidectin EP Impurity I

(23S) -23-des (methoxyimino) -23-[ (methylsulfanyl) methoxy]moxidectin; (2S,2a'E,2a1'S,4S,4'E,5S,6S,6'R,8'E,11'R,15'S,17a'R,20'R,20a'R) -2a1',20'-dihydroxy-5,6',8',19'-tetramethyl-6- ((E) -4-methylpent-2-en-2-yl) -4- ((methylthio) methoxy) -2a1',3,4,5,6,6',7',10',11',14',15',17a',20',20a'-tetradecahydro-2'H,17'H-spiro[pyran-2,13'-[11,15]methano[1,5]dioxacyclooctadecino[9,8,7-cd]benzofuran]-17'-one