This paper describes the interesting structural studies on three new diterpenoids (plant products), namely, hydroxy-dialactone nepetaefolinol (9,13-epoxy-6 β-hydroxy-8 α-labdane-16,15 :19,20-diolactone), dehydrated nepetaefolinol (9,13-epoxylabd-5-ene-16,15:19,20-diolactone) and isomeric tetrol (15,16-epoxy-labda-13(16),14-diene-6 β,9,17,19-tetrol: which is the reduction product of new diterpenoid leonotinin) isolated from Indian herbal plant Leonotis nepetaefolia (collected in the flowering season from Guindy area, Madras), and are found to be the major compounds in their extractions, so they are expected to possess the interesting pharmacological properties. In all three structures, the fused ring systems adopt distorted chair-chair, distorted chair and intermediate between 1,2-diplanar and half-chair and chair-chair conformations. In compounds 1 and 2, the twisted form of lactone rings are orthogonal to each other and make dihedral angle of 88.4(1) and 87.5(2)° with each other. The primary interaction between the molecules is van der Waal’s in nature.

Keywords: diterpenoid, leonotis nepetaefolia, hypotensive, antimicrobial, phosphodiesterase inhibitors, pharmacological

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