Ningalin B compounds which act as potent P-gp inhibitors, from references 45, 49, 50 and 51. (a) N3 [49]. (b) Compound 35. 1-(2-(4-(benzyloxy)-3-methoxyphenyl)-2-oxoethyl)-3,4-bis(3,4-dimethoxyphenyl)-1H-pyrrole-2,5-dione 1-(2-(2-bromo-5-methoxy-4-((3,4,5-trimethoxybenzyl)oxy) phenyl)-2-oxoethyl)-3,4-bis(3,4-dimethoxyphenyl)-1H-pyrrole-2,5-dione [50]. (c) Compound 23. 1-(2-(2-bromo-5-methoxy-4-((3,4,5-trimethoxybenzyl)oxy) phenyl)-2-oxoethyl)-3,4-bis(3,4-dimethoxyphenyl)-1H-pyrrole-2,5-dione [45]. (d) Compound 12. 1-(2-(4-(Benzyloxy)-5-bromo-2-(2-morpholinoethoxy)-phenyl)-2-oxoethyl)-3,4-bis(3,4-dimethoxy-phenyl)-1H-pyrrole2,5-dione [51].