Sphingosine kinases are enzymes that catalyze the biosynthesis of sphingosine-1-phosphate. The invention provides compounds that are effective for inhibition of sphingosine kinase type 1, sphingosine kinase type 2, or both. Certain compounds are selective for sphingosine kinase type 2 relative to sphingosine kinase type 1. Compounds of the invention can be used in treatment of a range of diseases wherein increasing the level of sphingosine-1-phosphate in blood is medically indicated. Diseases that can be treated by administration of an effective dose of a compound of the invention include a neoplastic disease that involves excess vascular growth; macular degeneration or diabetic retinopathy; an allergic disease such as asthma, an inflammatory disease of the eye such as uveitis, scleritis, or vitritis; an inflammatory disease of the kidney; a fibrotic disease; atherosclerosis; or pulmonary arterial hypertension. A compound of the invention can be used to improve the integrity of a vascular barrier in a disease where the vascular barrier is disrupted, such as cancer or Alzheimer's disease.