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Part I. the Total Synthesis Of AN ABSTRACT OF THE THESIS OF Lester Percy Joseph Burton forthe degree of Doctor of Philosophy in Chemistry presentedon March 20, 1981. Title: Part 1 - The Total Synthesis of (±)-Cinnamodialand Related Drimane Sesquiterpenes Part 2 - Photochemical Activation ofthe Carboxyl Group Via NAcy1-2-thionothiazolidines Abstract approved: Redacted for privacy DT. James D. White Part I A total synthesis of the insect antifeedant(±)-cinnamodial ( ) and of the related drimanesesquiterpenes (±)-isodrimenin (67) and (±)-fragrolide (72)are described from the diene diester 49. Hydro- boration of 49 provided the C-6oxygenation and the trans ring junction in the form of alcohol 61. To confirm the stereoselectivity of the hydroboration, 61 was convertedto both (t)-isodrimenin (67) and (±)-fragrolide (72) in 3 steps. A diisobutylaluminum hydride reduction of 61 followed by a pyridiniumchlorochromate oxidation and treatment with lead tetraacetate yielded the dihydrodiacetoxyfuran102. The base induced elimination of acetic acid preceded theepoxidation and provided 106 which contains the desired hydroxy dialdehydefunctionality of cinnamodial in a protected form. The epoxide 106 was opened with methanol to yield the acetal 112. Reduction, hydrolysis and acetylation of 112 yielded (t)- cinnamodial in 19% overall yield. Part II - Various N- acyl- 2- thionothiazolidineswere prepared and photo- lysed in the presence of ethanol to provide the corresponding ethyl esters. The photochemical activation of the carboxyl function via these derivatives appears, for practical purposes, to be restricted tocases where a-keto hydrogen abstraction and subsequent ketene formation is favored by acyl substitution. Part 1 The Total Synthesis of (±)-Cinnamodial and Related Drimane Sesquiterpenes. Part 2 Photochemical Activation of the Carboxyl Group via N-Acy1-2-thionothiazolidines. by Lester Percy Joseph Burton A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy Completed March 20, 1981 Commencement June 1981 APPROVED: Redacted for privacy Profesool-of Chemistry,in charge of major Redacted for privacy Head of Department of Chemistry Redacted for privacy Dean of Gr duate School' Date thesis is presented March 20, 1981 Typed by Janice Lum for Lester Percy Joseph Burton To Mom, Dad and Barry et pour mes Grandparents ACKNOWLEDGEMENTS I wish to express my deepest thanksto Dr. James D. White for his enthusiastic support and guidanceduring my tenure at Oregon State University. A special debt of gratitude is owed tomy wife, Katie, and both our families for their unfailingencouragements. Finally, I wish to acknowledge the Murdock Trust and the NationalScience Foundation for their support of this work. TABLE OF CONTENTS PART 1. THE TOTAL SYNTHESIS OF (±)-CINNAMODIAL AND RELATED DRIMANE SESQUITERPENES I Introduction 3 II Synthesis of (t)-Isodrimenin and (±)-Fragrolide 17 III Synthesis of (t)-Cinnamodial 29 IVExperimental 43 V Bibliography 65 PART 2. PHOTOCHEMICAL ACTIVATION OF THE CARBOXYL GROUP VIA N-ACYL-2-THIONOTHIAZOLIDINES I Introduction 70 II Preparation and Photolysis of N- Acyl- 2- thionothiazolidines 79 III Experimental 88 IV Bibliography 92 Part I The Total Synthesis of (±)-Cinnamodial and Related Drimane Sesquiterpenes Part 2 Photochemical Activation of the Carboxyl Group via N-Acy1-2-thionothiazolidines 2 PART 1 THE TOTAL SYNTHESIS OF (±)-CINNAMODIAL AND RELATED DRIMANE SESQUITERPENES I. INTRODUCTION In recent years, it has becomeapparent that there exists in nature, a group of substances with theability to cause cessation of feeding in insects. These "antifeedant" compounds, which have been isolated from a variety of plantsources, are active at exceedingly high dilution, typically inthe microgram per litrerange. 1 Antifeedants (formally classifiedas phagorepellants) have attracted the attention of insectphysiologists and agricultural econo- mists for their unique andpotentially beneficial properties.Conceiv- ably these substancesor structural analogues could provide nontoxic, nonpolluting, species-specific deterrentsto devastating insect infes- tations. The mechanism by which the antifeedant effectoperates is unknown. However, in at least onecase, strong inhibition of the res- piratory reactions in the mitochondriahas been shown to occur.2 A research group at the InternationalCenter for Insect Physiology and Ecology (ICIPE) in Nairobi, Kenya,has been particularly successful in isolating and establishing thestructures of plant products with 2-10 phagorepellant properties. For example, Nakanishi and Kubo have identified vegetation with unusualresistance to predation by insects, and the antifeedants isolated from theseplants have been tested suc- cessfully against two species of the Africanarmy worm (Spodoptera 11 littoralis and Spodoptera exempta) and the desert locust (Schisto- 2 cerca gregaria ). These insects are voracious and widespread African crop pests, yet it is found that feeding can be completely halted by 13 minute quantities of these natural repellants. Depending on the do- sage level, the cessation of feeding is temporary or permanent. Insect mortality was attributed to starvation rather than cytotoxicityof the antifeedant. Among the antifeedants isolated bythe research group at ICIPEare 14 15 3 cinnamodial (1), polygodial (2), warburganal (3), and muzigadial 4 (4). These substances are found in theleaves, heartwood and bark of the East African trees Warburgiaugandensis and W. stuhlmanii. Polygo- dial (2) has also been isolatedfrom Polygonum hydropiper L., the water CHO 12 R 1 1 R1=0Ac' R2=0H 4 2 R1 =R2=H 3 R1 =11, R2=0H 16 17 18 pepper, and several names, tadeon, tadeonal and tadenal, have been proposed for this compound by independentresearch groups. The 19 name ugandensidial was proposed for 1 until it was recognized that the same substance had been isolated previouslyfrom a tree in Madagas- car, Cinnamosma fragrans Baillon, from whence thename cinnamodial was adopted. The various parts of the plants from which these substances were isolated have been commonly used in African folk medicine and also 20 as spices. Polygodial (2), structurally the simplest of these four dialdehydes, is the least active antifeedant andis deactivated by epimerization of the C-9 aldehyde with base.Warburganal (3) has re- ceived most of the attention in thisgroup since it has very high anti- feedant potency. Muzigadial (4) has recently been shown to have 5 comparable activity to warburganal (3). Cinnamodial (1), though found to be a weaker antifeedant than warburganal (3) or muzigadial (4), has recently been shown to be as potent against Spodoptera species. The four dialdehydes 1-4 belong structurally to the drimane family ofses- 21 quiterpenes, a large number of which are presently known.Moreover, a recent report has indicated that antifeedants of this enedialdehyde class may have broader distribution than the terrestrial plant kingdom, since rhipocephenal (5), isolated from a Caribbean green alga (Rhipo- cephalus phoenix), was found to inhibit feeding of herbivorous fish and provided an effective defensive weapon for this alga in the marine en- 22 vironment. 5 In addition to the five compounds cited above, there exists a variety of unrelated substances reported to exhibit antifeedant ac- 5 tivity. For example, N-methylflindersine (6), isolated from the bitter root bark of Fagara chalybea, F. holstii (Rutaceae) and Xylo- carpus granatum (Meliaceae), has been shown to be effective against Spodoptera species and against the Mexican bean beetle (Epilachna 6 varivestis). Isodomedin (7), an ent-kaurenoid diterpene, was ex tracted from the bitter principles of Isodon Skikokianus var inter- medius, and was also found to exhibit activity against larvae of the 6 7 7,12 2 African army worm. Azadirachtin (8) and meliantriol (9),1 iso- lated from Melia azadiracta L. (the Indian Neem tree), are both potent against the desert locust. The former is the more active and 8 also exhibits activity against the tobacco bud worm larvae (Heliothis verescens), the adult cabbage moth (Pieris brassica), the termite lar- vae (Teticuli termis), the coffee bug (Antestiopsis), the tobacco horn- worm (Manduca sexta) and the vagrant grasshopper (Shistocerca vaga). 8 9 8 The leaves of Ajuga remota have yielded the ajugarins (10) (ent- clerodanes) which are moderately strong antifeedants. From the East and West African plant, Schkuhria pinnata, two new bitter heliangolides, 9 the schkuhrins (11) (germacrolides) have been isolated.Both the 7 ajugarins and the schkuhrinswere effective against the African army worm, and the latter were also active against the Mexican bean beetle. OH OR OAc 11 10 R= COCHOHCH(CH ) R=H or R=Ac or R=Ac The bitter principle of the unripe fruit of Xylocarpus molluscensis,to which aphrodisiac prOpertiesare attributed by folklore, yielded xylo- 2 mollin (12), a secoiridoid, which is yet another Africanarmy worm HO HO 12 10 phagorepellant. The first phenolic glycoside, myricoside (13), iso- lated from the roots of the bush Clerodendrum myricoides, also exhibits antifeedant properties. Many of these substances, first isolated at ICIPE, were discovered with the help of informationprovided by "Bwana ,23 Mganga", the local medicine man..1 In addition to their phagorepel- lant properties, many of these compounds exhibit varyingdegrees of antitumor, antifungal, antiyeast, plant growth regulatory,antibac- terial, cytotoxic, and molluscicidal activity. Since 1974, when chemical workon antifeedants began at ICIPE, a number
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