ERROR opening https://cactus.nci.nih.gov/chemical/structure/O%3DP%28O%29%28O%29COCCn1c2ncnc%28c2nc1%29N/file?format=sdf&get3d=True  -- O%3DP%28O%29%28O%29COCCn1c2ncnc%28c2nc1%29N could not be loaded.