Stereoselective synthesis and moulting activity of integristerone A and analogues Saowanee Kumpun, a Boon-ek Yingyongnarongkul, a Ren e Lafont, b Jean-Pierre Girault c and Apichart Suksamrarn a, * a Department of Chemistry, Faculty of Science, Ramkhamhaeng University, Bangkok 10240, Thailand b Laboratoire de Biochimie Structurale et Fonctionnelle des Prote´ines, Universite´ Pierre et Marie Curie, CNRS FRE 2852, 7 Quai St. Bernard, 75252 Paris 05, France c Laboratoire de Chimie et Biochimie Pharmacologiques et Toxicologiques, Universite´ Paris V-Rene ´ Descartes, CNRS UMR 8601, 45 rue des Saints-P eres, 75270 Paris Cedex 06, France Received 19 September 2006; revised 8 November 2006; accepted 23 November 2006 Abstract—Integristerone A, a rare ecdysteroid of plant origin, has been synthesized from 20-hydroxyecdysone with 2-deoxy-1,2-didehydro- 20-hydroxyecdysone as the key intermediate, followed by stereoselective asymmetric dihydroxylation. The analogues 1,2-di-epi-integrister- one A and 1,2-di-epi-5a-integristerone A have also been synthesized. Integristerone A exhibited approximately 9-fold lower moulting activity than the parent 20-hydroxyecdysone in the Musca domestica bioassay, indicating that the presence of a 1b-hydroxyl group resulted in a decrease in activity. As expected, the 1,2-di-epi-5a-analogue was inactive in this assay. Ó 2006 Elsevier Ltd. All rights reserved. 1. Introduction Integristerone A (1) is a member of the 1,2,3-trihydroxyste- roids, a rare and relatively small group of ecdysteroids, the arthropod moulting hormones. 1 This compound was first iso- lated from the plant Rhaponticum integrifolium. 2 No synthe- sis of 1,2,3-trihydroxy ecdysteroids has been reported to date. This paper deals with a concise, stereoselective synthesis of compound 1 and its analogues from 20-hydroxyecdysone (2). 2. Results and discussion 2.1. Synthesis of integristerone A (1) and analogues The synthesis of compound 1 is outlined in Scheme 1. The readily available starting material 20-hydroxyecdysone (2) 3 was subjected to selective 20,22-acetonidation to the corre- sponding 20,22-acetonide 3 using acetone and p-TsOH. 4 Selective mesylation by treatment of a pyridine solution of 3 with MsCl afforded the mesylate 4 in 86% yield, which was acetylated to the corresponding acetate 5 in 95% yield. Elimination of MsOH from 5 to yield the olefin 6 using a num- ber of bases was attempted, but unsatisfactory results were obtained. It was not surprising that elimination of MsOH was not a facile step, since a molecular model indicated that the C-1 hydrogen and the C-2 MsO group could assume an antiperiplanar conformation only when the A-ring adopted the less preferred boat conformation. However, we eventually found that DBU effected the required elimination reaction of 5 in DMF solution at 150  C to give the required olefin 6 in 64% yield together with the minor C-5 epimer 7 in 13% yield. The absence of the MsO signal and the presence of H-1 (d, J¼10 Hz) and H-2 (dd, J¼10, 4.4 Hz) signals at d 5.95 and 5.73 in the 1 H NMR spectrum of 6 established its structure. The stereochemistry at C-3 was preserved as evident from the small W 1/2 value (10 Hz) of H-3. Other spec- troscopic (IR and MS) spectra were consistent with structure 6. Compound 6 was deacetylated with 10% K 2 CO 3 in MeOH to yield compound 8 in 74% yield, which was subsequently subjected to acetonide deprotection using 70% aq AcOH in the presence of the phase-transfer catalyst, benzyltrimethyl- ammonium chloride, to give compound 9 in 81% yield. The less polar olefin 7, the C-5 epimer of 6, was obtained as the minor component. This implied that C-5 epimerization had taken place at some stage in the reaction leading to Keywords: Ecdysteroid; Integristerone A; Synthesis; Moulting activity. * Corresponding author. Tel.: +662 3190931; fax: +662 3191900; e-mail: apichart@ram1.ru.ac.th 0040–4020/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.tet.2006.11.063 Tetrahedron 63 (2007) 1093–1099