Protected DHA units, known as dioxanones, are interesting compound which can be used as the building blocks for synthesis of polyoxygenated natural products. The direct aldol reaction is employed for converting of those inexpensive starting materials into enantioenriched products of complexed structures. The stereocontrol in the first aldol reaction is achieved by using organocatalysis. Second aldol reaction is conducted by lithium enolate chemistry leading to anticisanti aldols as a major isomer. On the other hand boron chemistry provides antitransanti products. This strategy is used for synthesis of higher sugars.

Protected DHA units, known as dioxanones, are interesting compound which can be used as the building blocks for synthesis of polyoxygenated natural products. The direct aldol reaction is employed for converting of those inexpensive starting materials into enantioenriched products of complexed structures. The stereocontrol in the first aldol reaction is achieved by using organocatalysis. Second aldol reaction is conducted by lithium enolate chemistry leading to anticisanti aldols as a major isomer. On the other hand boron chemistry provides antitransanti products. This strategy is used for synthesis of higher sugars.

Clostridium difficile is a Gram-positive bacterium that is the most common cause of hospital-associated and antimicrobial-associated diarrhea in humans. Monteiro and co-workers have discovered that C. difficile expresses three cell-surface polysaccharides, named PS-I, PS-II and PS-III. Interestingly, PS-I was determined to be present in a ribotype 027 strain, the ribotype responsible for recent deadly outbreaks worldwide. In this work, the total chemical synthesis of the PS-I pentasaccharide with a linker molecule by a linear synthesis strategy from four monosaccharide building blocks is described: α-L-Rhap-(1→3)-β-D-Glcp-(1→4)-α-D-Glcp-(1→2)-α-D-Glcp-(1→O(CH2)5NH2 3 ↑ 1 α-L-Rhap The synthesized PS-I pentasaccharide will be conjugated to a protein carrier for evaluation as an anti-C. difficile glycoconjugate vaccine.

With emerging trends of new cellular therapies, the need for quick access to cellular components is necessary. For most applications genetically compatible biological components are essential to prevent adverse immune responses and graft-versus host disease (GVHD). Since these biological components have a limited window to be used, techniques for long-term storage are needed. Cryopreservation is essential for this in the field of biobanking and regenerative medicine to allow for long-term storage of cell products. During this process, ice recrystallization is the major contributor to cell death and decreased cell viability post-thaw. Due to this, controlling ice growth and recrystallization is imperative to increasing cell survival and function. The Ben lab is focused on the synthesis of small molecule, carbohydrate-based cryoprotectants that function as ice recrystallization inhibitors (IRIs). Previously, many IRIs have been synthesized showing varying degrees of ice recrystallization inhibition (IRI). Through the structure-function work, a delicate balance between hydrophobic and hydrophilic portions on the same molecule must be met. These compounds are believed to disrupt hydrogen bonding networks present in the formation of ice, and control ice growth. While numerous types of functional groups on carbohydrate derivatives have been explored, many highly solvated functional groups (amines, sulfates, phosphates, etc.) have not been thoroughly investigated. Highly solvated functional groups should disrupt hydrogen bond networks due to their solvation and in theory, should illicit an IRI response. Sulfate groups have not previously been studied, but are present in several different biological processes, such as immune response and blood coagulation. This suggests that sulfated carbohydrates should be well tolerated biologically. Sulfate groups can also be easily installed on existing IRI active molecules through orthogonal protecting group chemistry. The first part of this thesis is focused on the synthesis and IRI activity of sulfated carbohydrates based upon previously synthesized, IRI active pyranose derivatives. When compared to their parent compounds, most of the sulfated derivatives were less active, but all compounds were incredibly soluble in aqueous media. These derivatives did not show much promise as new IRIs due to the length of their synthesis and reduced IRI activity compared to their parent compounds. The Ben lab has also developed a new class of IRI active carbohydrates: aldonamide derivatives. These compounds are open-chain carbohydrates with an amide bond, arising from the ring opening of a carbohydrate lactone with a substituted amine. While many of these compounds displayed high degrees of IRI activity, many were incredibly insoluble in aqueous systems (many with solubility limits under 50 mM). Since sulfate groups were able to greatly increase solubility with some derivatives retaining IRI activity, installing sulfate groups on existing aldonamide-based IRIs should increase their solubility. Additionally, since many of these derivatives display high degrees of IRI activity, a reduction in IRI activity can be tolerated. Similarly, to the sulfated pyranose derivatives, the presence of a sulfate group reduced the IRI activity compared to the parent compounds in most derivatives. Though some sulfated derivatives possessed a higher degree of IRI activity, all the derivatives experienced a drastic increase in solubility (over 200 mM in PBS). Some of the sulfated aldonamide derivatives were assessed for their ability to protect red blood cells (RBCs) during freezing with reduced glycerol concentrations (15% glycerol), although none of thew tested derivatives showed an improvement over existing IRIs explored by the Ben lab. Since the introduction of sulfate groups to existing IRIs drastically increased solubility in aqueous systems, but resulted in reduced IRI activity in most compounds, focus was switched to the addition of different hydrophilic functional groups. Amino functional groups were briefly explored with galactose-based pyranose IRIs, aldonamide derivatives had not been explored. Amino groups are present on many biological carbohydrates and should be well tolerated biologically. The addition of amino groups to aldonamide derivatives should increase solubility, with the amino derivatives ideally retaining some IRI activity. The amino aldonamide derivatives synthesized had high solubilities (>500 mM in PBS), but did possess lower degrees of IRI activity. Due to the high solubility these derivatives were initially assessed in the cryopreservation of RBCs with reduced glycerol concentrations. Initial experiments showed improvements over current IRIs, and the compounds were assessed in a number of other biological cryopreservation scenarios including articular cartilage, platelets, and hematopoietic stem/progenitor cells (HSPCs). While the compounds showed toxicity in these cell types, more studies need to be conducted for the cryopreservation of RBCs.

There has been increasing interest in the syntheses of carbohydrates due to their profound role in various biological processes and thus their potential in drug development. Various methods have been developed for the preparation of these oligosaccharides from simpler carbohydrate derivatives both chemically and enzymatically but they must be carefully applied to obtain the desired linkages. The main method that has been used to control the regioselectivity of glycosylations is protecting group chemistry. Unfortunately this requires additional steps lengthening the synthesis sequence. Extensive literature has shown the ability for carbohydrate recognition via organoboron methods through selective binding and their ability to undergo regioselective glycosylation through sugar-derived boronate esters. Exploiting these factors and in extension of previous work done in our laboratory on borinic acid- and boronic acid-catalyzed regioselective glycosylations of carbohydrate derivatives, we proposed a target oriented synthesis of a pentassacharide moiety found in four saponins isolated from Spergularia ramosa.

There has been increasing interest in the syntheses of carbohydrates due to their profound role in various biological processes and thus their potential in drug development. Various methods have been developed for the preparation of these oligosaccharides from simpler carbohydrate derivatives both chemically and enzymatically but they must be carefully applied to obtain the desired linkages. The main method that has been used to control the regioselectivity of glycosylations is protecting group chemistry. Unfortunately this requires additional steps lengthening the synthesis sequence. Extensive literature has shown the ability for carbohydrate recognition via organoboron methods through selective binding and their ability to undergo regioselective glycosylation through sugar-derived boronate esters. Exploiting these factors and in extension of previous work done in our laboratory on borinic acid- and boronic acid-catalyzed regioselective glycosylations of carbohydrate derivatives, we proposed a target oriented synthesis of a pentassacharide moiety found in four saponins isolated from Spergularia ramosa.

Thesis advisor: Jia Niu / Thesis advisor: Jim Morken / Polysaccharides make up one of the largest classes of nature’s macromolecules. However, they are severely understudied relative to other biomolecules such as proteins and DNA sequences. This is because discrete polysaccharides are difficult to isolate from nature or synthesize in laboratories in large enough quantities for thorough research. Polymerization is an efficient route to polysaccharides, yet has historically suffered from harsh conditions and lack of control. Herein, we investigate recent developments in the field of living polymerization as strategies towards synthesis of precision polysaccharides from 1,2- anhydrosugars. We specifically focus on cationic ring opening polymerization (ROP) and reversible addition-fragmentation chain transfer (RAFT) ROP polymerization of 1,2-O-Bn-3,4,6-anhydromannose and 1,2-O-Bn-3,4,6-anhydroglucose. Our research screens various catalyst/initiating systems. Our findings demonstrate that cationic ROP and RAFT polymerization are unsuccessful in the living ROP of 1,2-anhydrosugars. / Thesis (MS) — Boston College, 2023. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Four analogues of the Lewis X trisaccharide antigen (β-D-Galp(1→4)[α-L-Fucp(1→3)]-D-GlcNAcp) in which the galactosyl residue is modified at O-4 as a methyloxy, deoxychloro, deoxyfluoro or deoxy were synthesized. The preparation of the modified 4-OMe, 4-Cl, 4-F and 4-H trichloroacetimidate galactosyl donors is described as well as their use in the glycosylation of an N-acetylglucosamine glycosyl acceptor. The resulting disaccharides were deprotected at O-3 of the glucosamine residue and fucosylated giving access to the desired protected Lewis X analogues. One step global deprotection (Na/NH3) of the protected 4”-methoxy and 4”-deoxy analogues, and two step deprotections (removal of a p-methoxybenzyl with DDQ, then Zemplén deacylation) of the 4”-deoxychloro and 4”-deoxyfluoro protected Lex analogues gave the desired compounds in good yields. The relative binding energies of the 4” manipulated Lewis X methyl glycoside analogues for anti-Lewis X mAb SH1 were determined using competitive ELISA procedures. The binding experiments revealed that substitution of the 4” site with a deoxychloro, deoxyfluoro or deoxy function had a large differential change in the free energy of binding; yet they did not completely abolish cross reactivity with native Lewis X. Substitution with a methyloxy function eliminated recognition by anti-Lewis X monoclonal antibody SH1. / NSERC

No description available.

A doença de Chagas, também conhecida como tripanossomíase americana, é uma das doenças tropicais mais devastadoras e é causada pelo protozoário Trypanosoma cruzi. O parasita expressa uma enzima de superfície, Trypanosoma cruzi trans-sialidase (TcTS), responsável pela transferência de ácidos siálicos de células do hospedeiro para moléculas de -galactose terminais presentes em glicoproteínas de sua superfície. As moléculas de glicoproteína sialiladas estão envolvidas na adesão e subsequente penetração do parasita em células hospedeiras. Logo, TcTS desempenha papel fundamental no reconhecimento e na invasão de células do hospedeiro. Além disso, a ausência de trans-sialidase em seres humanos faz de TcTS um alvo potencial a ser explorado, no entanto nenhum inibidor desta enzima (em concentração nanomolar) é conhecido até o momento. Considerando a importância da unidade de galactose e da função carboxila do ácido siálico para interações no sítio activo de TcTS, focamos na síntese de derivados de galactose com ácido succínico em diferentes posições do anel de açúcar e sua avaliação biológica em TcTS. Além disso, foi proposta uma busca por novos inibidores de TcTS através de técnicas de modelagem molecular, como triagem virtual baseada no sítio ativo da enzima. -D-galactose e -Dgalactopiranosídeo de metila, disponíveis comercialmente, foram tratados com reagentes adequados para fornecer alguns intermediários com apenas uma hidroxila livre em poucas etapas. O tratamento destes compostos com anidrido succínico em piridina levou à formação dos respectivos derivados com ácido succínico em todas as posições do anel galactosídico. Após etapa de desproteção foi obtido apenas o derivado com ácido succínico na posição 4 (85), que foi testado em TcTS por ensaio fluorimétrico in vitro para avaliação de sua atividade inibitória. Adicionalmente, 85 foi testado em ensaios in vitro para avaliação de sua atividade tripanocida e citotóxica. De acordo com os ensaios biológicos, o composto 85 apresentou atividade inibitória promissora (56%) na concentração de 1,0 mM. Esse resultado preliminar foi importante para mostrar que esse tipo de derivado pode atuar como inibidor de TcTS e para orientar a síntese de novos derivados de galactose. O valor da atividade tripanocida foi inferior a 40% (0,5 mM) e não foi observada citotoxicidade na concentração de 0,5 mM. Os estudos de triagem virtual realizados neste trabalho através de simulações de \"docking\" resultaram na seleção das 50 melhores moléculas, baseada na orientação de maior pontuação, dentre 50.000 encontradas na base de dados diverset. O próximo passo envolve novos estudos para filtrar as moléculas mais promissoras para serem testadas em TcTS. / Chagas\' disease, also known as American trypanosomiasis, is one of the most devastating tropical diseases and it is caused by the protozoan Trypanosoma cruzi. The parasite expresses a cell surface enzyme, Trypanosoma cruzi trans-sialidase (TcTS), responsible for the transference of sialic acids from host cells to terminal -galactose molecules present on its glycoprotein surface. The sialylated glycoprotein molecules are involved in the attachment and subsequent penetration of the parasite into host cells. As a result, TcTS plays a key role in the recognition and invasion of host cells. Moreover, the lack of trans-sialidase in humans makes TcTS a potential drug target to be explored, however no strong inhibitors (at nanomolar range) of this enzyme are known to date. Considering the importance of galactose unit and the carboxyl function in sialic acid for interactions in the active site of TcTS, we have focused on the synthesis of galactose derivatives containing succinic acid in different positions of the sugar ring and on their biological evaluation against TcTS. In addition, we have proposed the search for new TcTS inhibitors applying molecular modeling techniques, like virtual screening based on the enzyme´s active site. Commercially available ,-D-galactose and methyl--D-galactopyranoside were treated with suitable reagents to afford some intermediates with just one free hydroxyl group in few steps. Treatment of these compounds with succinic anhydride in pyridine afforded derivatives thereof with succinic acid in all galactosidic ring positions. After deprotection step it was only obtained the derivative containing succinic acid at position 4 (85), which was tested in in vitro TcTS fluorimetric assay for evaluation of its inhibitory activity. In Addition, 85 was tested in in vitro assays for assessment of their trypanocidal activity and cytotoxic. According to the biological assays, compound 85 showed promising inhibitory activity (56%) at 1.0 mM concentration. This preliminary result was important both to show that this type of derivative can act as an inhibitor of TcTS and to guide the synthesis of new derivatives of galactose. The trypanocidal activity value was lower than 40% (0.5 mM) and there was no cytotoxicity at 0.5 mM concentration. The virtual screening studies performed in this work through docking simulations resulted in the selection of the 50 top-ranked molecules, based in the highest score orientation, among 50.000 found at diverset data base. The next step involves new studies to filter the most promising molecules to be tested against TcTS.