The Experts below are selected from a list of 309 Experts worldwide ranked by ideXlab platform
Pradip Kumar Samanta - One of the best experts on this subject based on the ideXlab platform.
-
stereoselective synthesis of the c3 c12 subunit of laulimalide
Tetrahedron Letters, 2014Co-Authors: Sadagopan Raghavan, Pradip Kumar SamantaAbstract:Abstract A stereoselective synthesis of the C3–C12 subunit of the tumor growth inhibitors laulimalide is disclosed. The key steps of the synthesis include asymmetric alkylation using Oppolzer’s protocol and an asymmetric hetero-Diels–Alder reaction using Jacobsen’s catalyst. Substrate controlled diastereoselective Luche Reduction followed by Ferrier type reactions are other key steps.
-
Stereoselective synthesis of the C3–C12 subunit of laulimalide
Tetrahedron Letters, 2014Co-Authors: Sadagopan Raghavan, Pradip Kumar SamantaAbstract:Abstract A stereoselective synthesis of the C3–C12 subunit of the tumor growth inhibitors laulimalide is disclosed. The key steps of the synthesis include asymmetric alkylation using Oppolzer’s protocol and an asymmetric hetero-Diels–Alder reaction using Jacobsen’s catalyst. Substrate controlled diastereoselective Luche Reduction followed by Ferrier type reactions are other key steps.
-
Stereoselective Synthesis of the Macrolactone Core of (+)-Neopeltolide
2012Co-Authors: Sadagopan Raghavan, Pradip Kumar SamantaAbstract:A stereoselective synthesis of the macrolactone core of the potent anticancer agent neopeltolide is disclosed. The key steps of the synthesis include asymmetric allylation using Krische’ protocol, conjugate Reduction using MacMillan’s methodology, and an asymmetric hetero-Diels–Alder reaction using Jacobsen’s catalyst. Substrate controlled diastereoselective 1,3-anti Reduction of a keto alcohol, Luche Reduction followed by Ireland–Claisen rearrangement, oxymercuration, and reductive lithiation are other key steps
Thitima Pengsuparp - One of the best experts on this subject based on the ideXlab platform.
-
synthesis chromatographic resolution and anti human immunodeficiency virus activity of calanolide a and its enantiomers
Journal of Medicinal Chemistry, 1996Co-Authors: Michael T Flavin, John D Rizzo, Albert Khilevich, Alla Kucherenko, Abram Kivovich Sheinkman, Vilayphone Vilaychack, Lin Lin, Wei Chen, Eugenia Mata Greenwood, Thitima PengsuparpAbstract:The anti-HIV agent (±)-calanolide A (1) has been synthesized in a five-step approach starting with phloroglucinol [→ 5 → 6 → 11 → 18 → (±)-1], which includes Pechmann reaction, Friedel−Crafts acylation, chromenylation with 4,4-dimethoxy-2-methylbutan-2-ol, cyclization, and Luche Reduction. Cyclization of chromene 11 to chromanone 18 was achieved by employing either acetaldehyde diethyl acetal or paraldehyde in the presence of trifluoroacetic acid and pyridine or PPTS. Luche Reduction of chromanone 18 at lower temperature preferably yielded (±)-1. Reduction of chromone 12, synthesized by Kostanecki−Robinson reaction from chromene 11, failed to afford (±)-1. The synthetic (±)-1 has been chromatographically resolved into its optically active forms, (+)- and (−)-1. The anti-HIV activities for synthetic (±)-1, as well as resultant (+)- and (−)-1, have been determined. Only (+)-1 accounted for anti-HIV activity, which was similar to the data reported for the natural product, and (−)-1 was inactive.
-
Synthesis, chromatographic resolution, and anti-human immunodeficiency virus activity of (±)-calanolide A and its enantiomers
Journal of medicinal chemistry, 1996Co-Authors: Michael T Flavin, John D Rizzo, Albert Khilevich, Alla Kucherenko, Vilayphone Vilaychack, Lin Lin, Wei Chen, Eugenia Mata Greenwood, Sheinkman Abram Kivovich, Thitima PengsuparpAbstract:The anti-HIV agent (±)-calanolide A (1) has been synthesized in a five-step approach starting with phloroglucinol [→ 5 → 6 → 11 → 18 → (±)-1], which includes Pechmann reaction, Friedel−Crafts acylation, chromenylation with 4,4-dimethoxy-2-methylbutan-2-ol, cyclization, and Luche Reduction. Cyclization of chromene 11 to chromanone 18 was achieved by employing either acetaldehyde diethyl acetal or paraldehyde in the presence of trifluoroacetic acid and pyridine or PPTS. Luche Reduction of chromanone 18 at lower temperature preferably yielded (±)-1. Reduction of chromone 12, synthesized by Kostanecki−Robinson reaction from chromene 11, failed to afford (±)-1. The synthetic (±)-1 has been chromatographically resolved into its optically active forms, (+)- and (−)-1. The anti-HIV activities for synthetic (±)-1, as well as resultant (+)- and (−)-1, have been determined. Only (+)-1 accounted for anti-HIV activity, which was similar to the data reported for the natural product, and (−)-1 was inactive.
Weidong Zhang - One of the best experts on this subject based on the ideXlab platform.
-
Deoxygenation of α,β-Unsaturated Acylphenols Through Ethyl o-Acylphenylcarbonates with Luche Reduction.
ChemInform, 2013Co-Authors: Weidong ZhangAbstract:The reaction shows a very good selectivity as well as tolerance for a wide range of functional groups.
-
Deoxygenation of α,β-unsaturated acylphenols through ethyl o-acylphenylcarbonates with Luche Reduction
Tetrahedron Letters, 2013Co-Authors: Hu Yuan, Hao Chen, Hui-zi Jin, Rongcai Yue, Yun-heng Shen, Lei Shan, Qingyan Sun, Weidong ZhangAbstract:Abstract An efficient protocol for deoxygenation of α,β-unsaturated acylphenols through ethyl o -acylphenylcarbonates with Luche Reduction is described. The reaction shows very good selectivity and tolerates a wide range of functionalities on α,β-unsaturated acylphenols, giving corresponding 2-allylphenols in good to excellent yields.
Michael T Flavin - One of the best experts on this subject based on the ideXlab platform.
-
Synthesis of dual 14C‐labeled (+)‐calanolide A, a naturally occurring anti‐HIV agent
Journal of Labelled Compounds and Radiopharmaceuticals, 1997Co-Authors: Subbareddy Gaddam, John D Rizzo, Albert Khilevich, Crist N. Filer, Jeremey Giltner, Michael T FlavinAbstract:[10,18-14C]-(+)-Calanolide A [(+)-6] was synthesized in four steps from chromeno-coumarin 2. A Ti-mediated aldol reaction of 2 with [1,2-14C]-acetaldehyde stereoselectively produced the desired syn diastereomer (±)-3, with carbons at the 13 and 14 positions being 14C-labeled. Intermediate (+)-3 was isolated by lipase-catalyzed kinetic resolution and cyclized under Mitsunobu conditions to afford (+)-trans-2,3-dimethyl chroman-4-one, (+)-5. Luche Reduction on (+)-5 in EtOH/THF at −78°C led to the formation of dual 14C-labeled (+)-6 with a specific activity of 49.25 mCi/mmol. The overall radiochemical yield was 4.3% based on the starting 14C-acetaldehyde. © 1997 John Wiley & Sons, Ltd.
-
synthesis chromatographic resolution and anti human immunodeficiency virus activity of calanolide a and its enantiomers
Journal of Medicinal Chemistry, 1996Co-Authors: Michael T Flavin, John D Rizzo, Albert Khilevich, Alla Kucherenko, Abram Kivovich Sheinkman, Vilayphone Vilaychack, Lin Lin, Wei Chen, Eugenia Mata Greenwood, Thitima PengsuparpAbstract:The anti-HIV agent (±)-calanolide A (1) has been synthesized in a five-step approach starting with phloroglucinol [→ 5 → 6 → 11 → 18 → (±)-1], which includes Pechmann reaction, Friedel−Crafts acylation, chromenylation with 4,4-dimethoxy-2-methylbutan-2-ol, cyclization, and Luche Reduction. Cyclization of chromene 11 to chromanone 18 was achieved by employing either acetaldehyde diethyl acetal or paraldehyde in the presence of trifluoroacetic acid and pyridine or PPTS. Luche Reduction of chromanone 18 at lower temperature preferably yielded (±)-1. Reduction of chromone 12, synthesized by Kostanecki−Robinson reaction from chromene 11, failed to afford (±)-1. The synthetic (±)-1 has been chromatographically resolved into its optically active forms, (+)- and (−)-1. The anti-HIV activities for synthetic (±)-1, as well as resultant (+)- and (−)-1, have been determined. Only (+)-1 accounted for anti-HIV activity, which was similar to the data reported for the natural product, and (−)-1 was inactive.
-
Synthesis, chromatographic resolution, and anti-human immunodeficiency virus activity of (±)-calanolide A and its enantiomers
Journal of medicinal chemistry, 1996Co-Authors: Michael T Flavin, John D Rizzo, Albert Khilevich, Alla Kucherenko, Vilayphone Vilaychack, Lin Lin, Wei Chen, Eugenia Mata Greenwood, Sheinkman Abram Kivovich, Thitima PengsuparpAbstract:The anti-HIV agent (±)-calanolide A (1) has been synthesized in a five-step approach starting with phloroglucinol [→ 5 → 6 → 11 → 18 → (±)-1], which includes Pechmann reaction, Friedel−Crafts acylation, chromenylation with 4,4-dimethoxy-2-methylbutan-2-ol, cyclization, and Luche Reduction. Cyclization of chromene 11 to chromanone 18 was achieved by employing either acetaldehyde diethyl acetal or paraldehyde in the presence of trifluoroacetic acid and pyridine or PPTS. Luche Reduction of chromanone 18 at lower temperature preferably yielded (±)-1. Reduction of chromone 12, synthesized by Kostanecki−Robinson reaction from chromene 11, failed to afford (±)-1. The synthetic (±)-1 has been chromatographically resolved into its optically active forms, (+)- and (−)-1. The anti-HIV activities for synthetic (±)-1, as well as resultant (+)- and (−)-1, have been determined. Only (+)-1 accounted for anti-HIV activity, which was similar to the data reported for the natural product, and (−)-1 was inactive.
-
Synthesis of (+)-calanolide A, an anti-HIV agent, Via enzyme-catalyzed resolution of the aldol products
Tetrahedron: Asymmetry, 1996Co-Authors: Albert Khilevich, Michael T Flavin, John D Rizzo, Lin Lin, Wei Chen, Aye Aye Mar, S. Dzekhtser, D. Brankovic, Heping Zhang, Shuyuan LiaoAbstract:Abstract The synthesis of (+)-calanolide A ( 1 ), an anti-HIV-1 agent, is described. A TiCl 4 -mediated aldol reaction of compound 2 stereoselectively produced the desired syn diastereomer (±)- 5 , which was resolved by a lipase-catalyzed acylation reaction. Under Mitsunobu conditions (Ph 3 P/DEAD), the syn aldol product (+)- 5 led to the formation of trans -2,3-dimethyl chroman-4-one [(+)- 3 ] with 94% ee , while the anti aldol product (+)- 6 yielded both trans and cis derivatives (+)- 3 and (+)- 4 with 60% and 68% ee , respectively. Luche Reduction on (+)- 3 led to (+)- 1 and (+)-calanolide B in a ratio of 9:1.
Sadagopan Raghavan - One of the best experts on this subject based on the ideXlab platform.
-
stereoselective synthesis of the c3 c12 subunit of laulimalide
Tetrahedron Letters, 2014Co-Authors: Sadagopan Raghavan, Pradip Kumar SamantaAbstract:Abstract A stereoselective synthesis of the C3–C12 subunit of the tumor growth inhibitors laulimalide is disclosed. The key steps of the synthesis include asymmetric alkylation using Oppolzer’s protocol and an asymmetric hetero-Diels–Alder reaction using Jacobsen’s catalyst. Substrate controlled diastereoselective Luche Reduction followed by Ferrier type reactions are other key steps.
-
Stereoselective synthesis of the C3–C12 subunit of laulimalide
Tetrahedron Letters, 2014Co-Authors: Sadagopan Raghavan, Pradip Kumar SamantaAbstract:Abstract A stereoselective synthesis of the C3–C12 subunit of the tumor growth inhibitors laulimalide is disclosed. The key steps of the synthesis include asymmetric alkylation using Oppolzer’s protocol and an asymmetric hetero-Diels–Alder reaction using Jacobsen’s catalyst. Substrate controlled diastereoselective Luche Reduction followed by Ferrier type reactions are other key steps.
-
Stereoselective Synthesis of the Macrolactone Core of (+)-Neopeltolide
2012Co-Authors: Sadagopan Raghavan, Pradip Kumar SamantaAbstract:A stereoselective synthesis of the macrolactone core of the potent anticancer agent neopeltolide is disclosed. The key steps of the synthesis include asymmetric allylation using Krische’ protocol, conjugate Reduction using MacMillan’s methodology, and an asymmetric hetero-Diels–Alder reaction using Jacobsen’s catalyst. Substrate controlled diastereoselective 1,3-anti Reduction of a keto alcohol, Luche Reduction followed by Ireland–Claisen rearrangement, oxymercuration, and reductive lithiation are other key steps