No description available.

<p>Part I: Extensive studies for treating hypercholesterolemia, one of the major causes of human morbidity throughout the world, have led to the development of statin drugs-the most prevalent drug prescribed today. In addition to statins, SCH 351448 has attracted considerable interest from many synthetic groups as it is the only selective activator of low-density lipoprotein receptor (LDL-R) containing structural features such as a C2-symmetry and 2,6-cis-tetrahydropyrans. Even though direct dimerization has been the most efficient method for the construction of C2-symmetric macrodiolides, total syntheses of SCH 351448 were only achived by stepwise dimerizations. In this chapter, attempts were made to exploit the inherent C2-symmetric macrodioloide via direct dimerization using various single monomeric units, but they did not prove to be viable. Therefore, formal synthesis of SCH 351448 was accomplished through two tandem sequences; cross-metathesis/conjugate addition and allylic oxidation/conjugate addition reactions, to stereoselectively construct 2,6-cis-tetrahydropyrans embedded in SCH 351448. The 1,4-syn aldol and the Suzuki coupling reactions were effective for the construction of the monomeric units. This convergent route should be broadly applicable to the synthesis of a diverse set of analogues of SCH 351448 for further biological studies.</p><p>Part II: Histone deacetylases (HDACs) play a significant role in tumorigenesis and have been recognized as one of the target enzymes for cancer therapy. Extensive studies in small molecules inhibiting HDAC enzymes have resulted in pan-HDAC inhibitor suberoylanilide hydroxamic acid (SAHA) and class I HDAC inhibitor FK228, approved by FDA in 2006 and 2009, respectively. Recently, largazole, a natural product was isolated from Symploca sp. presented HDAC inhibitory activity. Due to its unique differential cytotoxicity, potency, and class selectivity, structure-activity relationship (SAR) studies of largazole have been achieved to improve the potency and class selectivity. In addition to such biological activities, pharmacokinetic characteristics and isoform selectivity should be improved for the therapeutic potential of cancer therapy. In this chapter, two types of largazole analogues were synthesized by a convergent route that involved an efficient and high yielding multistep sequence. The synthesis of three disulfide analogues to improve pharmacokinetics and five linker analogues to enhance HDAC isoform selectivity is disclosed. The evaluation of biological studies is in progress.</p> / Dissertation

Made available in DSpace on 2015-05-14T13:00:08Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 7127283 bytes, checksum: 26b433761ccb1d15fbc422d3d6da7f5b (MD5) Previous issue date: 2014-02-24 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Despite the investments in the search for more effective cancer therapies, the high incidence and mortality produced by this disease continue to increase, which has provoked public health problems to the population. In parallel to the progress of this situation, it has been found a breakthrough in the medicinal chemistry allowing synthesis of a variety of compounds, encouraging researchers into new structures with rich therapeutic potential. The synthesis of compounds derived from tetrahydropyran nucleus (DNT) has been receiving attention, considering the broad of biological activity from these structures. Therefore, the aim of this study was to analyze the cytotoxic activity of 31 DNT compounds. Cell viability was determined by MTT reduction and neutral red stain (CVN) assays. From such 31 compounds studied, only 42a-c and 43a - c showed potent cytotoxic effect on human cancer lines (K562, HL-60, HT-29 and MCF- 7) and a less significant cytotoxic effect on non-cancerous cells (L929 and PBMC cells) were shown. The leukemic cell lines K562 and HL-60 were the most sensitive ones. Compounds 42b and 43c, with IC50 values which range from 8.97 ± 4.1 to 35.35 ± 5.2 for the lines HL-60 and K562, were considered the most promising molecules in terms of their cytotoxic effect and they also demonstrated in primary cultures of peripheral blood and bone marrow from patients with chronic myeloid leukemia. The ability of 42b and 43c compounds to induce molecular changes related to the type of cell death was assessed by flow cytometry. In K562 cells, the compounds 42b and 43c showed similar effect causing an increase in the concentration of hipodiploide DNA and they arrested in the G1 phase of the cell cycle. From double labeling annexin/IP assay, the compound 43c increased about 20% of PI fluorescence. For HL-60 cell line, the compounds 42b and 43c augmented the concentration of hipodiploide DNA and and depolarization of mitochondrial membrane. The compound 43c stimulated ROS production and double staining to annexina/IP. Compounds 42b and 43c showed a potent cytotoxic effect and antileukemic activity, inducing apoptosis and cell cycle. However, there is a need for structural modifications that increase the selectivity of these compounds for cancer cells. / Apesar dos investimentos na busca de terapias mais eficazes contra o câncer, as elevadas taxas de incidência e mortalidade provocadas por esta doença, continuam a crescer, consistindo assim, um dos principais problemas de saúde pública. Em paralelo ao avanço dessa patologia, houve um avanço na química medicinal que permite a síntese de uma variedade de compostos, favorecendo a investigação de novas estruturas com excelentes perspectivas terapêuticas. A síntese de compostos derivados do núcleo tetraidropiranos (DNT) vem recebendo atenção, considerando a ampla atividade biológica dessas estruturas. Sendo assim, o objetivo desse estudo foi analisar a atividade citotóxica de compostos DNT. A viabilidade celular foi determinada pelos ensaios de redução do sal de MTT e CVN. Dos 31 compostos DNT estudados, 42a-c e 43a-c demonstraram potente efeito citotóxico em linhagens cancerígenas (K562, HL-60, HT- 29, MCF-7), e um efeito citotóxico menos expressivo em células não cancerígenas (L929, PBMC), as linhagens leucêmicas humanas K562 e HL-60 foram as mais sensíveis. Os compostos 42b e 43c, com valores de CI50 que variam de 8,97 ± 4,1 a 35,35 ± 5,2 para as linhagens HL-60 e K562, foram considerados os mais promissores, demonstrando também um efeito citotóxico similar em cultura primária de sangue periférico e de medula óssea de pacientes com leucemia mieloide crônica. A capacidade destes compostos provocarem alterações moleculares associadas ao tipo de morte celular foi avaliada por citometria de fluxo. Na linhagem K562, os compostos 42b e 43c tiveram efeito semelhante, provocando um aumento na concentração do DNA hipodiploide e parada na fase G1 do ciclo celular. No ensaio com dupla marcação anexina/iodeto de propídeo (IP) o composto 43c aumentou 20% de fluorescência para o IP. Para a linhagem HL-60, os compostos 42b e 43c induziram aumento da concentração de DNA hipodiploide, nas maiores concentrações, além de induzir despolarização na membrana mitocondrial. Apenas o composto 43c estimulou produção de EROs, e 42b e 43c aumentaram a dupla marcação para anexina/IP. Desta forma, observa-se que os compostos 42b e 43c apresentaram um potente efeito citotóxico e atividade antileucêmica, sendo capazes de induz apoptose e parada no ciclo celular, porém há ainda necessidade de modificações estruturais que aumentem a seletividade destes compostos para células cancerígenas.

Polyketide secondary metabolites constitute a structurally-diverse and clinically-important family of natural products. The wide range of biological activities represented by these substrates have contributed to therapeutic agents with annual sales exceeding $20B USD. Large multi-domain proteins called polyketide synthases (PKSs) use simple building blocks to generate highly-oxygenated and stereochemically-rich frameworks with astonishing selectivity. These substrates often feature rigidifying biases imposed by macrocyclic lactones and substituted heterocycles, which can impact their bioactive conformation. The work of this dissertation combines synthetic chemistry and biochemistry to investigate chemoenzymatic production of macrocyclic polyketide natural products. Research focused on validating a transannular oxa-conjugate addition strategy to assembly 2,6-cis-tetrahydropyran (THP) ring systems, as demonstrated by synthesis of the macrocyclic core to neopeltolide. Ultimately, we wish to apply this chemistry to de novo PKS pathways for rapid, reliable, and sustainable production of THP-bearing products like neopeltolide, and toward building SAR libraries. Additionally, a second study probed the specificity of the macrolactonizing thioesterase (TE) domain from the 6-deoxyerythronolide B (DEBS) biosynthetic pathway. This pathway is the paradigm for type-I PKS systems, and is responsible for producing the macrolide core of erythromycin. Our on-going research evaluates the limits of promiscuity within this specific catalytic domain, to characterize the structural elements required to accurately predict macrolactonization. The long-term goal of this study is to assess the potential applicability of DEBS TE as a generalized cyclization biocatalyst for combinatorial biochemistry and chemoenzymatic research.

In 2004, the polyketide natural product, chamuvarinin (72) was isolated by Laurens et al. from the roots of Uvaria chamae, a member of the Annonaceae plant family. This unique tetrahydropyran containing acetogenin displayed potent levels of cytotoxic activity against the KB 3-1 cell line with an ED50 value of 0.8 nM. Upon initial isolation the relative and absolute stereochemical assignment of chamuvarinin (72) was unable to be readily achieved through ¹H and ¹³C NMR analysis. The initial synthetic route described herein has enabled the relative and absolute stereochemical determination of chamuvarinin (72) through the first total synthesis completed in 20 longest linear steps in 1.5% overall yield. A revised synthetic strategy towards chamuvarinin (72) was completed in 17 longest linear steps in 2.2% overall yield. The revised route facilitated the assembly of non-natural chamuvarinin-like analogues and their trypanocidal and cytotoxic activities have been assessed. The synthesis of these analogues has formed the basis of a more focussed study through the design and synthesis of simplified triazole (295), isoxazole (325) and butenolide triazole (305) analogues as potential Trypanosoma brucei (causative agent in African Sleeping sickness) inhibitors.

Les hétérocycles sont des motifs présents dans un grand nombre de produits naturels et synthétiques possédant une activité biologique. Le développement de méthodes pour construire ces motifs constitue un axe de recherche important et de nombreuses voies de synthèse ont été et sont encore aujourd'hui étudiées. Au cours de ces travaux de thèse, plusieurs méthodologies ont été développées permettant l'accès à de nouveaux hétérocycles: Une première étude sur l'hydrogénation des indoles et sur l'influence de leur substitution a été réalisée. Ces travaux ont permis de mettre au point une méthode simple et efficace pour obtenir des indoles partiellement ou totalement saturés. Dans un second temps la mise au point de conditions sans solvant et sans métal pour la réaction de cyclisation de Prins a conduit à l'isolation de tetrahydropyranes et à leur utilisation de manière séquentielle avec la réaction de Bartoli. Ces conditions se sont également avérées très efficaces pour la formation de sultames. Enfin, une approche synthétique vers les decytospolides A et B a été réalisée en utilisant comme réaction clé la réaction de cyclisation de Prins / The heterocyclic skeleton is present in many natural and synthetic products with biological activity. The development of methods to build these patterns is an important area of research and many synthetic routes have been and are still being studied. During this work, several methods have been developed allowing access to new heterocyclic compounds: first the hydrogenation of indoles and the influence of their substitution was realised. This work allowed to develop a simple, selective and efficient method to obtain partially or fully saturated indoles. Next the development of neat and metal-free conditions for the Prins cyclization reaction gave tetrahydropyrans and was sequentially used with the Bartoli reaction. These conditions have also proved to be very efficient for sultam synthesis. Finally, a synthetic approach to decytospolides A and B was performed using the Prins cyclization reaction as key step

Made available in DSpace on 2015-05-14T13:21:22Z (GMT). No. of bitstreams: 1 ArquivoTotal.pdf: 18195512 bytes, checksum: 6229ab5e9f367190d5f7b4336c07dfec (MD5) Previous issue date: 2013-08-30 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / This study was designed based on the concept of achiral / meso compound. The importance of preparing achiral compounds is based on their structural simplification, leading to new molecules which require no further investigations pharmacodynamics and pharmacokinetics of the enantiomers. Therefore, it is proposed to the synthesis of analogues tetrahydropyrans achiral/meso using the Prins cyclization reaction. The homoallylic alcohols synthesized in this work were derived from the Barbier reaction obtained in great yields, wherein these products are used as a synthesis intermediate for the preparation of tetrahydropyrans proposed. The Prins cyclization reaction is an efficient method for the preparation of tetrahydropyrans therefore proved to be a powerful tool for synthesis and versatile for the preparation of substituted tetrahydropyrans to give all the compounds synthesized in satisfactory yields. Through spectroscopic and crystallographic studies were possible to determine in detail the relative configuration of the molecules 40a, 41a, 44a, 45a, 46a, 46b and 48b. Furthermore, a theoretical study was developed using the density functional theory to obtain the molecular geometries optimized in the gas phase, making it possible to compare these preferred conformations with geometries defined by crystals. The tetrahydropyrans bioevaluated were synthesized in the leukemic cell line K562 and two types of normal L929 cells and PBMC. The results were very promising in cancer in vitro assays, highlighting the hydrazones 42a-c and the 43a-c aminoguanidines they were the only compounds that were active against resistant cell line K562, highlighting the tetrahydropyran 42c which showed higher activity series counterpart (present value of IC50 7.59 μM) and the tetrahydropyran 42b with an excellent IC50 (8.97 μM) value and a good selectivity index (2.2 in L929 and 1.6 in PBMC). / Este trabalho foi idealizado baseado no conceito de compostos aquirais/meso. A importância da preparação de compostos aquirais está baseada na sua simplificação estrutural, conduzindo a novas moléculas que não necessitam de posteriores investigações farmacodinâmicas e farmacocinéticas dos enantiômeros. Sendo assim, propomos neste trabalho a síntese de análogos tetraidropirânicos aquirais/meso utilizando a reação de ciclização de Prins. Os álcoois homoalílicos sintetizados foram provenientes da reação de Barbier obtidos em ótimos rendimentos, no qual estes produtos foram utilizados como intermediário de síntese para a preparação dos tetraidropiranos propostos. A reação de ciclização de Prins é um método eficiente na preparação dos tetraidropiranos, pois mostrou-se ser uma ferramenta de síntese poderosa e versátil para a preparação dos tetraidropiranos substituídos, obtendo-se todos os compostos sintetizados em rendimentos satisfatórios. Através de estudos espectroscópicos e cristalográficos foi possível determinar detalhadamente a configuração relativa das moléculas 40a, 41a, 44a, 45a, 46a, 46b e 48b. Além disso, foi desenvolvido um estudo teórico utilizando a teoria do funcional densidade para se obter as geometrias moleculares otimizadas em fase gasosa, tornando possível comparar estas conformações preferenciais com as geometrias definidas pelos cristais. Os tetraidropiranos sintetizados foram bioavaliados na linhagem de células leucêmicas K562 e dois tipos de células normais L929 e PBMC. Os resultados em câncer foram bastante promissores nos ensaios in vitro, dando destaque para as hidrazonas 42a-c e as aminoguanidinas 43a-c que foram os únicos compostos que se mostraram ativos contra a linhagem celular resistente K562, destacando-se o tetraidropirano 42c que apresentou maior atividade da série congênere (apresentando valor de CI50 7.59 μM) e o tetraidropirano 42b que apresentou excelente valor de IC50 (8.97 μM) e um bom índice de seletividade (2.2 em L929 e 1.6 em PBMC).

Made available in DSpace on 2015-05-14T13:21:40Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 9887169 bytes, checksum: df02b626a4888063d509afbbb46317e8 (MD5) Previous issue date: 2014-08-25 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / This work was presented using the technique of molecular hybridization which is a classic strategy in medicinal chemistry and useful in the design of new drugs, consisting of the covalent joining of two or more fragments known pharmacophoric or already present recognized therapeutic activities. Described the technique of extraction, isolation and purification of piperine 6 with 2% yield, with the same natural molecule mostly present in black pepper, where studies have shown a variety of biological activities as analgesic, anti-inflammatory, anti-thermal, antitumor, antifungal, antichagasic, insecticide, leishmanicidal, among others. Next, was performed the synthesis of the respective piperic acid 12 obtained via basic hydrolysis with 87% yield. A series of alcohols tetrahydropyran derivatives replaced (33, 34, 37, 38, 79 and 80) were synthesized in good yields (76% -100%), with synthetic route and potent antinociceptive already described by our group research. The Prins cyclization reaction was used as key step to build diastereoselective 2,4-cis and 2,4,6-cis tetrahydropyranyl rings. Subsequently, we performed the synthesis of 6 novel hybrid molecules (64, 65, 66, 67, 68 and 69), based on the structure of an analog of piperine (piperic acid) with 6 alcohols substituted tetrahydropyran derivatives, using the classical approach molecular hybridization by Steglich esterification reaction to join the two portions with relatively good yields (42% - 78%), which was the intention enhance the analgesic activity by these two chemical entities. All molecular hybrids were characterized by spectroscopic (1H and 13C) and IR / Neste trabalho foi apresentado o uso da técnica de hibridização molecular que é uma estratégia clássica em química medicinal e bastante útil na concepção de novos fármacos, consistindo na junção covalente de dois ou mais fragmentos reconhecidamente farmacofóricos ou que já apresentem atividades terapêuticas reconhecidas. Descreveu-se a técnica de extração, isolamento e purificação da piperina 6 com 2% de rendimento, sendo a mesma uma molécula natural presente principalmente na pimenta preta, onde estudos mostraram uma série de atividades biológicas como, analgésico, antiinflamatório, antitérmico, antitumoral, antifúngico, antichagásico, inseticida, leishmanicida, dentre outras. Em seguida, foi realizado a síntese do seu respectivo ácido pipérico 12 obtido via hidrólise básica com 87% de rendimento. Uma série de derivados álcoois tetraidropiranos substituídos (33, 34, 37, 38, 79 e 80) foram sintetizados em bons rendimentos (76%-100%), com rota sintética e potente atividade antinociceptiva já descritas pelo nosso grupo de pesquisa. A reação de ciclização de Prins foi usada como etapa chave para a construção, em forma diastereosseletiva 2,4-cis e 2,4,6-cis, dos anéis tetraidropiranos. Posteriormente, realizou-se a síntese de 6 moléculas híbridas inéditas (64, 65, 66, 67, 68 e 69), baseadas na estrutura de uma análogo da piperina (ácido pipérico) com os 6 derivados álcoois tetraidropiranos substituídos, utilizando a estratégia clássica de hibridização molecular através da reação de esterificação de Steglich para unir as duas porções, com rendimentos relativamente bons (42%-78%), onde o intuito foi potencializar a atividade analgésica apresentada por estas duas entidades químicas. Todos os híbridos moleculares foram caracterizados pelas técnicas de espectroscopia (1H e 13C) e infravermelho

Devant l’intérêt grandissant pour le développement de stratégies innovantes applicables à la synthèse de molécules complexes, notre groupe s’est orienté vers la construction de motifs présents dans un grand nombre de produits biologiquement actifs : les tétrahydropyranes (THP) et les polypropionates. Notre stratégie, basée sur la formation diastéréosélective de diols méso primaires, fait intervenir une étape inédite de désymétrisation organocatalysée par transfert d’acyle asymétrique. Cette approche permet la synthèse énantiosélective de THP pentasubstitués qui par la suite peuvent être valorisés par l’obtention de polypropionates fonctionnalisés, possédant quatre centres stéréogènes contigus. Par ailleurs, cette nouvelle méthodologie de désymétrisation donne accès à des motifs cycliques et acycliques comportant plusieurs centres stéréogènes quaternaires. Elle constitue, de plus, l’unique exemple de désymétrisation énantiosélective de diols méso primaires catalysée par une dialkylaminopyridine chirale. Bien que le transfert d’acyle asymétrique organocatalysé ait été très largement étudié depuis la fin des années 90, de nombreuses études sont en cours pour accéder à des catalyseurs plus sélectifs et plus nucléophiles. Inspiré des récents travaux de Steglich et Vedejs, notre deuxième objectif s’est porté sur la synthèse énantiosélective et modulaire d’une nouvelle famille d’organocatalyseurs chiraux plus polyvalents dérivés de la 1,6-naphtyridine. Leur application, en catalyse nucléophile, a pu être évaluée dans des réactions de dédoublement cinétique d’alcools et dans les réarrangements de Steglich. / Alongside metallocatalysis and biocatalysis, organocatalysis has emerged as a complementary and powerful tool that can circumvent limitations associated to the use of metals or enzymes. Because of the growing interest for new innovative methodologies useful for complex molecules synthesis, we get interested in the preparation of versatile building blocks present in many bioactive molecules: tetrahydropyrans (THP) and polypropionates. Based on the diastereoselective formation of primary meso diols, our strategy involves an original organocatalyzed desymmetrization of these compounds by asymmetric acyl transfer. This approach allows the enantioselective synthesis of pentasubstituted THP which were valorized through the synthesis of polypropionates bearing four consecutive stereogenic centers. In addition, this new methodology provides cyclic and acyclic scaffolds with several all carbon quaternary stereogenic centers. It represents the first example in organocatalyzed asymmetric desymmetrization by acyl transfer using a chiral dialkylaminopyridine. Although asymmetric organocatalyzed acyl transfer has been widely studied since the late 90s, several investigations are currently underway to access to new chiral nucleophilic catalysts. Following the recent work of Steglich and Vedejs, we were interested in the development of new chiral organocatalysts derived from 1,6-naphthyridine. Their applications in nucleophilic catalysis have then been evaluated in kinetic resolutions of alcohols and in asymmetric Steglich rearrangements.

Cet ouvrage traite de la formation diastéréosélective de tétrahydropyranes 3,7-cis et 3,7-trans polysubstitués. Des méthodologies de cycloétherification et de C-glycosidation en tandem avec une réduction radicalaire y sont décrites (pyranes 3,7- trans) tandis qu’une haloéthérification en tandem avec le même processus radicalaire conduit aux pyranes 3,7-cis. Suite à des travaux antérieurs du laboratoire, des études ont été réalisées afin de comprendre l’influence de la stéréochimie des substituants en position C3, C6, C7 et C8 sur l’issue diastéréochimique lors d’un transfert d’hydrure sous contrôle exocyclique sur un centre radicalaire adjacent à un tétrahydropyrane (C2). Ces études ont permis de solutionner les problèmes de diastéréosélectivité rencontrés lors des réductions radicalaires des centres en C2 de divers fragments élaborés d’ionophores (e.g. zincophorine, salinomycine, narasine…) réalisées par notre groupe. Des études conformationnelles réalisées sur des pyranes di- ou tri-substitués ont permis de comprendre les diastéréosélectivités notées lors du processus radicalaire en fonction des stéréochimies relatives des centres précédemment cités. En particulier, l’utilisation d’un bicycle rigide (trans-octahydrochromène) a permis de montrer l’importance du positionnement spatial (axial ou équatorial) de la chaîne portant le centre radicalaire. Par la suite, nous avons pu mettre en évidence une amplification des ratios en faveur du produit de réduction radicalaire 2,3-anti lorsque la réaction est réalisée en présence d’un acide de Lewis monodentate encombré (MAD). L’optimisation du contrôle endocyclique lors du transfert d’hydrure a permis de générer la stéréochimie complémentaire 2,3-syn. L’utilisation du TTMSS comme source d’hydrure combinée à l’utilisation d’un acide de Lewis bidentate tel que MgBr2·OEt2 a permis l’obtention d’excellentes sélectivités en faveur du produit endocyclique. Des études RMN 13C ainsi que le titrage des ions Mg2+ en solution ont été effectués afin de comprendre la nature des complexes impliqués. Finalement, ces études ont permis la formation stéréocontrôlée de centres stéréogéniques adjacents à un THP, motifs fréquement rencontrés dans certains policétides. Elles permettent ainsi d’envisager la synthèse de polyéthers de type ionophore et d’autres molécules d’intérêt biologique. / This work describes the diastereoselective formation of polysubstituted 3,7-cis and 3,7-trans tetrahydropyrans. Tandem radical reduction/cycletherification and tandem radical reduction/C-glycosidation methodologies are depicted for 3,7-trans pyrans formation while tandem radical reduction/haloetherification lead to 3,7-cis pyrans. Following previous work in the laboratory, studies have been conducted to better understand the stereochemical influence that substituents in the C3, C6, C7 and C8 positions have on the diastereoselectivity of a hydride transfer radical reaction on a radical center with an adjacent tetrahydropyran (exocyclic control). These studies have helped to solve diastereoselectivity problems encountered with C2 radical reductions in different ionophore fragments (e.g. zincophorin, salinomycin, narasin ...) that were investigated by our group. Conformational studies performed on di-or tri-substituted pyrans have helped to understand the diastereoselectivities observed in the radical process of the stereochemical centers mentioned above. In particular, the use of a bicycle frame (trans-octahydrochromene) showed the importance of the spatial positioning (axial or equatorial) of the radical center chain. Subsequently, we were able to demonstrate an increase ratios for the 2,3-anti radical reduction product when the reaction was performed in the presence of a bulky monodentate Lewis acid (MAD). Optimization of hydride transfer under endocyclic control has generated the complementary 2,3-syn stereochemistry. Use of TTMSS as a hydride source combined with the use of a bidentate Lewis acid such as MgBr2·OEt2 allowed for the formation of endocyclic products with excellent selectivities. 13C NMR studies and titration of Mg2+ ions in solution were performed to understand the nature of the complexes involved. Finally, these studies led to the stereocontrolled formation of stereogenic centers adjacent to a THP, motifs frequently encountered in polyketides. This work thus involves the synthesis of polyether ionophore-type fragments and other molecules of biological interest.