Cortisone (I) and hydrocortisone (X), Kendall's compounds E and F, have been converted to the corresponding 21-aldehydes, Δ⁴-3,11,20-triketo-17α-hydroxypregnene-21-al (V) and Δ⁴-3,20-diketo-11β,17α-dihydroxyprenene-21-al (XIII), which are biologically active. A new antibiotic, exhibiting highly specific in vitro activity against Mycobacteria, has been isolated from a species of Streptomyces; it is a monobasic acid (actithiazic acid) with low toxicity but no in vivo activity. The lowest boric ester, methyl borate, forms white solid addition compounds with a number of amines, while higher borates show less interaction, suggesting steric factors govern complex stability. The recent elucidation of serotonin's structure has provided an opportunity to test a postulate in non-infectious disease chemotherapy, leading to attempts to produce serotonin antimetabolites (e.g., 2-methyl-3-ethyl-5-aminoindole) for potential hypertension treatment.