Nodulisporic Acid B, B 1 , and B 2 : A Series of 1 0 -Deoxy-nodulisporic Acids from Nodulisporium sp. John G. Ondeyka,* Arlene M. Dahl-Roshak, Jan S. Tkacz, Deborah L. Zink, Michelle Zakson-Aiken, Wesley L. Shoop, Michael A. Goetz and Sheo B. Singh* Merck Research Laboratories, PO Box 2000, Rahway, NJ 07065, USA Received 13 March 2002; accepted 5 July 2002 Abstract—During the re-isolation of the lead compound nodulisporic acid A (1a) and targeted chemical screening for related compounds, we discovered a series of 1 0 -deoxy congeners named herein nodulisporic acids B (1b), B 1 (2b), and B 2 (3b). In com- parison with nodulisporic acid A, these compounds were less active and were chemically unstable resulting into formation of Á 23 dehydro derivatives. Therefore, these compounds were stabilized and isolated as sodium salts and methyl ester. Nodulisporic acid B is 100-fold less active than nodulisporic acid A against fleas. The isolation, structure elucidation, and biological activities of these compounds are described. # 2002 Elsevier Science Ltd. All rights reserved. Fleas and ticks pose a significant health hazards to companion animals. Although several topical flea-killing agents are available for dogs and cats, such as, fipronil, 1 imidacloprid, 2 and selamectin, 3 none is orally active. A long-duration, systemically active, non-toxic agent that can kill fleas on dogs or cats would be highly preferred over topical agents. A few years ago we reported 4 the discovery of nodulisporic acid A (1a), 4a A 1 (2a), 4b and A 2 (3a). 4b Nodulisporic acid A is a potent, long-lasting, nontoxic systemic orally-active agent that kills fleas on dogs 4c,d that became a significant medicinal chemistry lead for further potency and duration-of-action improve- ments. The mechanism-of-action of nodulisporic acid A was elucidated. 5 It exerts its biological activity by selectively opening an insect (invertebrate)-specific, glutamate- gated chloride channel, thus paralyzing insects without affecting the mammalian host. 5 During these investiga- tions we sought other structurally-related natural product derivatives by targeted chemical and biological screening either as minor congeners in the existing fermentation or as major products from mutants of the producing organism. These efforts led to the discovery of a series of1 0 -deoxy congeners, isolated initially from the original producing fungus Nodulisporium sp. as very minor components, named herein nodulisporic acids B (1b),B 1 (2b),andB 2 (3b).Subsequently,aseriesof Nodulisporium mutants was isolated that yielded these compounds as major components of the fermentation. The isolation, structure elucidation, and activity of these compounds are described in this paper. 0960-894X/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0960-894X(02)00621-2 Bioorganic & Medicinal Chemistry Letters 12 (2002) 2941–2944 *Corresponding authors. Tel.: +1-732-594-3222; fax: +1-732-594- 6880; e-mail: john_ondeyka@merck.com (J. G. Ondeyka); sheo_singh @meck.com (S. B. Singh)