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Rafael Pedrosa - One of the best experts on this subject based on the ideXlab platform.
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one pot sequential organocatalytic michael tishchenko lactonization reactions synthesis of enantioenriched 4 5 6 trisubstituted δ lactones
Journal of Organic Chemistry, 2014Co-Authors: James O Guevarapulido, Jose M Andres, Rafael PedrosaAbstract:Enantioenriched trisubstituted lactones were obtained in good yields and moderate to very good enantioselectivities in one-pot process, which implies a sequential organocatalyzed Michael addition of ketones to enals, followed by catalytic intramolecular diastereoselective Tishchenko reaction and lactonization. The final lactones were obtained as single diastereoisomers, demonstrating that the mixture of the anti and syn diastereomers epimerized to the syn Hydroxy Ester during the oxido-reduction step.
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One-Pot Sequential Organocatalytic Michael–Tishchenko–Lactonization Reactions. Synthesis of Enantioenriched 4,5,6-Trisubstituted δ‑Lactones
2014Co-Authors: James O. Guevara-pulido, José M. Andrés, Rafael PedrosaAbstract:Enantioenriched trisubstituted lactones were obtained in good yields and moderate to very good enantioselectivities in one-pot process, which implies a sequential organocatalyzed Michael addition of ketones to enals, followed by catalytic intramolecular diastereoselective Tishchenko reaction and lactonization. The final lactones were obtained as single diastereoisomers, demonstrating that the mixture of the anti and syn diastereomers epimerized to the syn Hydroxy Ester during the oxido-reduction step
James O Guevarapulido - One of the best experts on this subject based on the ideXlab platform.
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one pot sequential organocatalytic michael tishchenko lactonization reactions synthesis of enantioenriched 4 5 6 trisubstituted δ lactones
Journal of Organic Chemistry, 2014Co-Authors: James O Guevarapulido, Jose M Andres, Rafael PedrosaAbstract:Enantioenriched trisubstituted lactones were obtained in good yields and moderate to very good enantioselectivities in one-pot process, which implies a sequential organocatalyzed Michael addition of ketones to enals, followed by catalytic intramolecular diastereoselective Tishchenko reaction and lactonization. The final lactones were obtained as single diastereoisomers, demonstrating that the mixture of the anti and syn diastereomers epimerized to the syn Hydroxy Ester during the oxido-reduction step.
Jose M Andres - One of the best experts on this subject based on the ideXlab platform.
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one pot sequential organocatalytic michael tishchenko lactonization reactions synthesis of enantioenriched 4 5 6 trisubstituted δ lactones
Journal of Organic Chemistry, 2014Co-Authors: James O Guevarapulido, Jose M Andres, Rafael PedrosaAbstract:Enantioenriched trisubstituted lactones were obtained in good yields and moderate to very good enantioselectivities in one-pot process, which implies a sequential organocatalyzed Michael addition of ketones to enals, followed by catalytic intramolecular diastereoselective Tishchenko reaction and lactonization. The final lactones were obtained as single diastereoisomers, demonstrating that the mixture of the anti and syn diastereomers epimerized to the syn Hydroxy Ester during the oxido-reduction step.
Antonios G Mikos - One of the best experts on this subject based on the ideXlab platform.
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Hydroxyapatite fiber reinforced poly α Hydroxy Ester foams for bone regeneration
Biomaterials, 1998Co-Authors: Robert C Thomson, Michael J. Yaszemski, John M Powers, Antonios G MikosAbstract:A process has been developed to manufacture biodegradable composite foams of poly(DL-lactic-co-glycolic acid) (PLGA) and Hydroxyapatite short fibers for use in bone regeneration. The processing technique allows the manufacture of three-dimensional foam scaffolds and involves the formation of a composite material consisting of a porogen material (either gelatin microspheres or salt particles) and Hydroxyapatite short fibers embedded in a PLGA matrix. After the porogen is leached out, an open-cell composite foam remains which has a pore size and morphology defined by the porogen. By changing the weight fraction of the leachable component it was possible to produce composite foams with controlled porosities ranging from 0.47 +/- 0.02 to 0.85 +/- 0.01 (n = 3). Up to a polymer:fiber ratio of 7:6, short Hydroxyapatite fibers served to reinforce low-porosity PLGA foams manufactured using gelatin microspheres as a porogen. Foams with a compressive yield strength up to 2.82 +/- 0.63 MPa (n = 3) and a porosity of 0.47 +/- 0.02 (n = 3) were manufactured using a polymer:fiber weight ratio of 7:6. In contrast, high-porosity composite foams (up to 0.81 +/- 0.02, n = 3) suitable for cell seeding were not reinforced by the introduction of increasing quantities of Hydroxyapatite short fibers. We were therefore able to manufacture high-porosity foams which may be seeded with cells but which have minimal compressive yield strength, or low porosity foams with enhanced osteoconductivity and compressive yield strength.
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Bone formation by three-dimensional stromal osteoblast culture in biodegradable polymer scaffolds
Journal of Biomedical Materials Research, 1997Co-Authors: Susan L. Ishaug, Genevieve M. Crane, Michael J. Yaszemski, Michael J Miller, Alan W Yasko, Antonios G MikosAbstract:Bone formation was investigated in vitro by culturing stromal osteoblasts in three-dimensional (3-D), biodegradable poly(DL-lactic-co-glycolic acid) foams. Three polymer foam pore sizes, ranging from 150-300, 300-500, and 500-710 microns, and two different cell seeding densities, 6.83 x 10(5) cells/cm2 and 22.1 x 10(5) cells/cm2, were examined over a 56-day culture period. The polymer foams supported the proliferation of seeded osteoblasts as well as their differentiated function, as demonstrated by high alkaline phosphatase activity and deposition of a mineralized matrix by the cells. Cell number, alkaline phosphatase activity, and mineral deposition increased significantly over time for all the polymer foams. Osteoblast foam constructs created by seeding 6.83 x 10(5) cells/cm2 on foams with 300-500 microns pores resulted in a cell density of 4.63 x 10(5) cells/cm2 after 1 day in culture; they had alkaline phosphatase activities of 4.28 x 10(-7) and 2.91 x 10(-6) mumol/cell/min on Days 7 and 28, respectively; and they had a cell density that increased to 18.7 x 10(5) cells/cm2 by Day 56. For the same constructs, the mineralized matrix reached a maximum penetration depth of 240 microns from the top surface of the foam and a value of 0.083 mm for mineralized tissue volume per unit of cross sectional area. Seeding density was an important parameter for the constructs, but pore size over the range tested did not affect cell proliferation or function. This study suggests the feasibility of using poly(alpha-Hydroxy Ester) foams as scaffolding materials for the transplantation of autogenous osteoblasts to regenerate bone tissue.
Düsing Marion - One of the best experts on this subject based on the ideXlab platform.
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Synthese von optisch aktiven Tetronsäurederivaten â Schlüsselbausteine für eine Oxaspirodion-Totalsynthese
2011Co-Authors: Düsing MarionAbstract:Tetronsäuren stellen eine bedeutende Klasse der Naturstoffe dar. So finden sie sich immer wieder als Grundbaustein in neuen Substanzen mit hochinteressantem biologischen Eigenschaften. Eine für diese Arbeit besonders wichtige Substanz ist Oxaspirodion, das auch einen wichtiger Vertreter der Substanzklasse der Spiroverbindungen darstellt.rnDie Synthesen wurden mit der Zielsetzung geplant, eine möglichst vielfältige Auswahl an Synthesebausteinen zu erhalten, um einen flexiblen Zugang zu verschiedenen Tetronsäurederivaten zu entwickeln. Im Rahmen dieser Arbeit werden vier Wege vorgestellt, die es ermöglichen sollten, das Dienophil für eine spätere Totalsynthese des Oxaspirodions zu erschließen.rnSyntheseweg 1: Das Dienophil sollte aus einem ï¢-KetoEster über eine Reduktions-Eliminierungssequenz seiner Carbonylgruppe erhalten werden. Schlüsselschritt hier ist die Dieckmann-Cyclisierung eines ï¢-KetoEsters, der seinerseits aus Trimethyldioxinon und einem HydroxyEster synthetisiert wird. Syntheseweg 2: In einem alternativen Syntheseweg wird das Dienophil durch eine Knoevenagel-Kondensation der in 3-Position unsubstituierten Tetronsäure und einem Aldehyd erhalten. Syntheseweg 3: Die dritte Methode, die zu dem gewünschten Alkenylfuran führen sollte, ist die Umsetzung eines geeigneten Derivates mit Ketenylidentriphenylphosphoran 19, die Schobert in seinen Arbeiten vorstellte. Syntheseweg 4: Das Dienophil wird in der vierten Syntheseroute durch Iodlactonisierung und anschließender reduktiver Eliminierung durch AIBN und Tributylstannan erhalten.Tetronic acids are an important class of natural products. Several newly discovered members of this substance class show highly interesting biological properties. Of particularly importantance for this work is Oxaspirodione, which is also a major representative of the class of spiro compounds .rnThe syntheses were planned with the purpose to obtain a diverse range of possible building blocks to develop a flexible access to various tetronic acid derivatives . In this work, four different synthetic routes are presented to get a key intermediate for the synthesis of Oxaspirodion:rnSynthetic route 1: The key intermedieate, a dienophile, should be obtained from beta-keto Esters by a reduction-elimination sequence of its carbonyl group. The key step of this approach is the Dieckmann cyclization of a beta-keto Ester, which can be synthesized from Trimethyldioxinon and a Hydroxy Ester. Synthetic route 2: In an alternative synthesis the dienophile is obtained by a Knoevenagel condensation of the unsubstituted tetronic acid and an aldehyde. Synthetic route 3: The third method, which should lead to the desired alkenylfurane, is the reaction of a suitable precursor with a Ketenylidentriphenylphosphoran. Synthetic route 4: The dienophile is obtained by iodolactonization and subsequent reductive elimination by AIBN and tributylstannane
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Synthese von optisch aktiven Tetronsäurederivaten – Schlüsselbausteine für eine Oxaspirodion-Totalsynthese
09: Chemie Pharmazie und Geowissenschaft. 09: Chemie Pharmazie und Geowissenschaft, 2011Co-Authors: Düsing MarionAbstract:Tetronsäuren stellen eine bedeutende Klasse der Naturstoffe dar. So finden sie sich immer wieder als Grundbaustein in neuen Substanzen mit hochinteressantem biologischen Eigenschaften. Eine für diese Arbeit besonders wichtige Substanz ist Oxaspirodion, das auch einen wichtiger Vertreter der Substanzklasse der Spiroverbindungen darstellt.rnDie Synthesen wurden mit der Zielsetzung geplant, eine möglichst vielfältige Auswahl an Synthesebausteinen zu erhalten, um einen flexiblen Zugang zu verschiedenen Tetronsäurederivaten zu entwickeln. Im Rahmen dieser Arbeit werden vier Wege vorgestellt, die es ermöglichen sollten, das Dienophil für eine spätere Totalsynthese des Oxaspirodions zu erschließen.rnSyntheseweg 1: Das Dienophil sollte aus einem -KetoEster über eine Reduktions-Eliminierungssequenz seiner Carbonylgruppe erhalten werden. Schlüsselschritt hier ist die Dieckmann-Cyclisierung eines -KetoEsters, der seinerseits aus Trimethyldioxinon und einem HydroxyEster synthetisiert wird. Syntheseweg 2: In einem alternativen Syntheseweg wird das Dienophil durch eine Knoevenagel-Kondensation der in 3-Position unsubstituierten Tetronsäure und einem Aldehyd erhalten. Syntheseweg 3: Die dritte Methode, die zu dem gewünschten Alkenylfuran führen sollte, ist die Umsetzung eines geeigneten Derivates mit Ketenylidentriphenylphosphoran 19, die Schobert in seinen Arbeiten vorstellte. Syntheseweg 4: Das Dienophil wird in der vierten Syntheseroute durch Iodlactonisierung und anschließender reduktiver Eliminierung durch AIBN und Tributylstannan erhalten.Tetronic acids are an important class of natural products. Several newly discovered members of this substance class show highly interesting biological properties. Of particularly importantance for this work is Oxaspirodione, which is also a major representative of the class of spiro compounds .rnThe syntheses were planned with the purpose to obtain a diverse range of possible building blocks to develop a flexible access to various tetronic acid derivatives . In this work, four different synthetic routes are presented to get a key intermediate for the synthesis of Oxaspirodion:rnSynthetic route 1: The key intermedieate, a dienophile, should be obtained from beta-keto Esters by a reduction-elimination sequence of its carbonyl group. The key step of this approach is the Dieckmann cyclization of a beta-keto Ester, which can be synthesized from Trimethyldioxinon and a Hydroxy Ester. Synthetic route 2: In an alternative synthesis the dienophile is obtained by a Knoevenagel condensation of the unsubstituted tetronic acid and an aldehyde. Synthetic route 3: The third method, which should lead to the desired alkenylfurane, is the reaction of a suitable precursor with a Ketenylidentriphenylphosphoran. Synthetic route 4: The dienophile is obtained by iodolactonization and subsequent reductive elimination by AIBN and tributylstannane
