A short review on cardiotonic steroids and their analogues is presented. The natural, semisynthetic and synthetic derivatives, as well as their mechanism of action and structure-activity relationships are shown, with a special reference to aminoguanidine derivatives.

Biological Activities and Uses The use of pine resin as a whole or its derivatives, essence, and colophony as expectorants, modifiers of bronchial secretions, and antiseptics for the urinary tract, as weli as rubefacients and vessicants in poultices and creams in veterinary practice is described in several Pharmacognosy and Medicinal Plant treatises (66, 67). In recent years (i967-i992), studies on the biological activities of abietane acids have been performed with pure compounds and activities like antimicrobial, antiulcer, cardiovascular, allergenic, antiallergic, and many uses in cosmetics and dermatologic preparations have been reported for some of them. Antimicrobial Activity The antimicrobial activity of pisiferic acid (48) and its derivatives has been established against Pseudomonas, Proteus, and Klebsiella (68) as have its antibacterial actions against Gram-positive microorganisms, its antifungal activity, and its activity in experimental carcinoma of the uterus (HeLa-S3 cells) (55, 58). In the systems assayed, pisiferic acid (48) was active against Proteus vulgaris, Staphylococcus aureus, Bacillus subtilis, Pyricularia oryzae, and HeLa-S3 celis, while methylation of the

28 cyclolignans, most of them derived from podophyllotoxin, have been evaluated for their antineoplastic and antiviral activities. They were subjected to screening against P-388 murine leukemia, A-549 human lung carcinoma, and HT-29 colon carcinoma, while antiviral assays were performed on herpes simplex virus type I infecting fibroblasts of monkey kidney (HSV/CV-1) and on vesicular stomatitis virus infecting fibroblasts of hamster kidney (VSV/BHK). A number of substances were active in both groups of assays at concentrations below 1 microM; deoxypodophyllotoxin (1) being the most potent compound in all cases.

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Several series of nonlactonic podophyllic aldehyde analogues were prepared and evaluated against several human tumor cell lines. They had different combinations of aldehyde, imine, amine, ester, and amide functions at C-9 and C-9' of the cyclolignan skeleton. All the compounds synthesized showed cytotoxicity levels in the microM range and below. Within the new series tested, compounds having an aldehyde or imine at C-9 and an ester at C-9' were the most potent, with GI(50) values in the nM range, some of them being several times more potent against HT-29 and A-549 carcinoma than against MB-231 melanoma cells. Cell cycle studies and analysis of the microtubule-disrupting capacity have demonstrated the existence of two different mechanisms of cell death induction for compounds with closely related structures.

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