Faculty of Science School of Chemistry 9800165e govendor@aurum.wits.ac.za / Pyranonaphthoquinones are biologically important molecules found in a wide variety of bacteria, microbial fungi and plant species. Their biological activity is proposed to be a consequence of their ability to function as bioreductive alkylating agents. This class of compounds, which include monomeric and dimeric examples, contain the basic naphtho[2,3-c]pyran-5,10-dione skeleton, usually with substituents at the C-1 and C-3 positions of the pyran ring. The aim of the first part of the project was to develop a novel method for the synthesis of enantiomerically pure 5,8-dimethoxy-isochroman-4-ol, which will provide a handle for stereoselectively adding substituents to the C-1 and C-3 positions of the pyran nucleus. In the second part of the project we wished to attempt to synthesize the naturally occurring compound, cardinalin 3, the dimer of ventiloquinone L previously synthesized in the Wits laboratories. The synthesis of the enantiomerically pure isochromanol began with 2,5-dihydroxybenzoic acid, which was subjected to a diallylation followed by a Claisen rearrangement. The phenols were protected by a methylation reaction and the ester moiety was reduced to give (2-allyl-3,6- dimethoxyphenyl)methanol. It was then allylated to produce a suitable precursor for a one pot/two step ruthenium mediated isomerisation/ring closing metathesis reaction to produce 5,8-dimethoxy-1H-isochromene in an overall yield of 47%. It was converted to racemic 5,8-dimethoxy-isochroman-4-ol through a hydroboration-oxidation reaction in a yield of 84%. The separation of the enantiomers was achieved by acetylating the alcohol to form 5,8-dimethoxy-3,4-dihydro-1H-isochromen-4-yl acetate and then a lipase enzyme was used to stereospecifically deacetylate one enantiomer, while leaving the other enantiomer untouched. The second part of the dissertation discusses the progress towards the synthesis of cardinalin 3. This project began with the formation of the C-C biaryl axis starting from 1,3-dimethoxybenzene. The synthesis then continued with the diformylation of the biphenyl to give 2,2’,6,6’-tetramethoxy[1,1′-biphenyl]-3,3′-dicarbaldehyde. This was subjected to a Stobbe condensation and a Friedel-Crafts acylative cyclisation to produce diethyl [4,4′-diacetoxy-6,6′,8,8′-tetramethoxy-7,7′-binaphthalene]-2,2′- dicarboxylate. The synthesis will be continued in the PhD, using methodology previously developed for the formation of the monomer, as well as methodology developed here.

The thesis subject is mainly involved in Green Chemistry approach. Thiophene, furan and pyridine carboxaldehydes were chosen as starting compounds and vinylation and allylation with Grignard reaction afforded the corresponding racemic heteroaryl substituted allylic and homoallylic alcohols. Subsequent resolution with enzymes (PS-Amano II, Lipozym and Novazym 435) gave enantiomerically enriched alcohols with the e.e. values varied between 65 and 99%. The absolute configurations of all substrates are known. As a result of O-allylation with the common procedure formed the feasible carbon backbone for the ring closing metathesis reaction. All ring closing metathesis reactions were performed by Grubbs&rsquo / catalyst with just 5% catalyst loading. The absolute configurations of dihydrofuran and dihydropyran derivatives are known, since the chiral center configurations of all substrates are preserved throughout all the applied processes.

Optically active polychlorinated norbornene systems are important starting compounds for the synthesis of many complex molecules. The synthetic strategy of this study mainly depends upon the enzymatic resolution of hydroxymethyl-substituted polychlorinated norbornene structures. The enantiomerically enriched acetoxymethyl derivatives were synthesized in high ee values by several lipases. The absolute configuration of tetrachlorinated norbornene system was determined by X-ray analysis. The second part of the thesis involves the ruthenium and cerium-catalyzed oxidation reactions of various polychlorinated norbornene derivatives to afford &amp / #945 / -diketones. The regioselectivity of ruthenium catalyst was tested in polychlorinated norbornadiene systems. In the third part of the study, cyclopentanoid derivatives were synthesized in high chemical yield starting from enantio-enriched both tetra- and hexa-chlorinated norbornene derivatives. In the last part of the study, stereo- and regioselective synthesis of carbasugar systems which are potential glycosidase inhibitors were performed. Starting from enantio-enriched acetoxymethyl substituted tetrachloro norbornene system both carbasugar by cleavage of C1-C7 bond and &lsquo / confused&rsquo / carbasugar by cleavage of C4-C7 bond were synthesized.

The racemic homoallylic and homopropargylic alcohol derivatives were resolved by applying chemoenzymatic method using various lipase type enzymes i.e., PS-C II, Lipozyme, CAL-B. The enantiomeric excess values of the resultant alcohols were determined by HPLC. These enantiomerically enriched homoallylic and homopropargylic alcohols were subjected to N-propargylation and N-allylation, respectively, by SN2 and modified Mitsunobu reactions. During the course of all reactions, stereochemistry of the chiral centers were under controlling according to the known reaction mechanisms. The resultant chiral N-tosylated enyne derivatives afforded the corresponding chiral fused cyclopenta[c]pyridinone derivatives (69, 73, 75 and 77) with acceptable chemical yields and excellent diastereoslectivity depending upon the conformational effect on the complete remote stereochemical control for the newly generated chiral centers. The chemoenzymatic applications done with biocatalysis (lipases) and the Pauson-Khand reaction are involved in &ldquo / Green Chemistry&rdquo / approach.

The main subject of this thesis is synthesis of chiral diene systems via Ring Closing Enyne Metathesis (RCEM). Furan and thiophene carbaldehydes were chosen as starting compounds. As a result of allylation and propargylation reaction of these aldehydes targeting racemic heteroaryl substituted homoallylic and homopropargylic alcohols were synthesized. Enantiomerically enriched alcohols were obtained by enzymatic resolution method with different enzymes (PS-II, Lipozyme) with the high enantiomeric excess values. Absolute configurations of all alcohols are known. O-allylation and O-propargylation reactions of enantiomerically pure alcohols, afforded feasible enyne units for RCEM were synthesized successfully. All RCEM reactions were performed by using Grubbs&amp / #8223 / 1st generation catalyst. The absolute configuration of all chiral diene systems were known since during the course of the all reactions, configurations were preserved. As a last step, Diels-Alder reactions were applied to some of these chiral diene systems to get bicyclic compounds and comment on the stereoselectivity. Only one diastereomeric cycloadduct was observed as a result of Diels-Alder applications.

In this thesis, an intramolecular Pauson-Khand reaction of chiral enynes derived from homoallyl, allyl and homopropargyl alcohols is described. For this purpose, 2-heteroaryl substituted homoallyl, allyl and homopropargyl alcohols are easily and efficiently resolved through enzymatic resolution in a high ee (91-99%) with a known stereochemistry. Each enantiomerically enriched enyne derived from homoallyl and homopropargyl alcohols affords the conformationally most stable diastereomeric cyclopenta[c]pyran ring system as a sole product, whereas enantiomerically enriched enynes derived from allyl alcohols give the diastereomeric cis:trans mixture of cyclopenta[c]furan ring system. In addition these, an intramolecular Pauson&ndash / Khand reaction of camphor tethered enynes derived from homoallyl, homomethallyl, and homopropargyl alcohols is also described. Accordingly, homoallyl, homomethallyl, and homopropargyl moieties are easily constructed on the camphor carbonyl group with excellent diastereoselectivity due to endo-face selectivity, and with known stereochemistry. Each enantiomerically pure enyne affords the conformationally most stable diastereomeric spirocyclic cyclopenta[c]pyran ring system.

ABSTRACT SYNTHESIS AND ENZYMATIC RESOLUTION OF VARIOUS CYCLOPENTENOID AND CYCLOHEXENOID TYPE COMPOUNDS iyig&uuml / n, &Ccedil / igdem Ph. D., Department of Chemistry Supervisor: Prof. Dr. Cihangir Tanyeli June 2005, 174 pages The aim of this thesis is to synthesize enantiomerically enriched cyclopentenoid and cyclohexenoid type of compounds with quaternary carbon stereocenters that are the simplest precursors of the complex natural products. The first part of the study involves the preparation of &amp / #945 / &#039 / -acetoxy &amp / #945 / &#039 / -substituted &amp / #945 / ,&amp / #946 / -unsaturated cyclic ketones. Methylation, ethylation, benzylation and allylation of cyclohexenone and cyclopentenone derivatives are performed. Then, these compounds are regioselectively oxidized at the &amp / #945 / &#039 / -position by Mn(OAc)3. This is the first successful example in the literature that &amp / #945 / &#039 / -tert-position is oxidized by Mn(OAc)3. The oxidations were also performed by Pb(OAc)4 and both methods were compared. Related to this study, in the second part, the enantiomeric resolution of the acetoxy derivatives were performed by various hydrolases. This study is the first example where the hydrolases are used to resolve tertiary positions. Among the enzymes used, Candida cylindracea lipase (CCL) showed the best enantioselectivity.

An applicable method for the racemic synthesis of 1,2-amino alcohols having tertiary alcohol moiety was developed. This method can be used as a general method for the synthesis of various 1,2-amino alcohols with various tertiary alcohol moieties by changing chloroacetone with different monohalo ketones, and with different aryl halides or alkyl halides. The resultant racemic 1,2-aminoe alcohols were tried to resolve by using various hydrolase type enzymes under different conditions by changing the parameters i.e. solvent, temperature and substrate: enzyme ratios. Finally, poorly resolved amino alcohol 20 with 21 % was used as chiral ligand in diethyl zinc reaction to benzaldhyde and afforded (R)-1-phenylpropan-1-ol almost with 21 % e.e..

Thesis (Ph, D.)--Miami University, Dept. of Chemistry and Biochemistry, 2008. / Title from second page of PDF document. Includes bibliographical references (p. 77-83).

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