Browsing by Author "Dalvi, Prashant B."

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Design, synthesis and diversification of natural product-inspired hydantoin-fused tetrahydroazepino indoles
(2015-01-01)
Barve, Indrajeet J.
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Dalvi, Prashant B.
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Thikekar, Tushar Ulhas
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Chanda, Kaushik
;
Liu, Yu-Li
A facile and efficient synthesis of novel oxo, thio and seleno hydantoin fused tetrahydroazepino [4,5-b] indoles was reported. A naturally occurring iboga class alkaloid inspired seven-membered azepino[4,5-b] indole ring was synthesized as a new scaffold through Pictet-Spengler reaction followed by skeletal rearrangement of the aziridine ring. To improve the efficiency of the synthetic route, the double bond of the rearranged olefinic product 5 was reduced and a privileged hydantoin moiety was constructed on the core system through urea formation using a variety of isocyanates, isothiocyanates and isoselenocyanates followed by intramolecular cyclization to incorporate elements of diversity. The regeneration of the double bond of intermediate 9 afforded hydantoin-fused tetrahydroazepino [4,5-b] indoles.
Diastereoselective Synthesis of Bridged Polycyclic Alkaloids via Tandem Acylation/Intramolecular Diels-Alder Reaction
(2013-10-04)
Chen, Chih-Hau
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Yellol, Gorakh S.
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Tsai, Cheng-Hsun
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Dalvi, Prashant B.
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Sun, Chung-Ming
A mild and efficient stereoselective synthesis of hexacyclic indole alkaloids with a tetrahydro-beta-carboline motif has been developed by utilizing the Pictet-Spengler reaction and tandem N-acylation followed by intramolecular Diels-Alder cyclization. Initially, a diene unit was installed in the tetrahedron beta-carboline skeleton through Pictet-Spengler cyclization of the corresponding aldehyde with tryptophan ester. The dienophile moiety was introduced by N-acylation of tetrahydro-beta-carboline. Successive, in situ, [4 + 2] intramolecular Diels-Alder cycloaddition of the activated dienophile and conjugated diene containing intermediate furnished bridged polycyclic heterocycles with high diastereoselectivity. Formation of four new rings, five new covalent bonds, and five new chiral centers with excellent stereoselectivity is the key, feature of this strategy. The diastereoselective formation of product was attributed to intramolecular chirality transfer through a chiral amino acid. The stereoselective outcome of this tandem reaction was confirmed by X-ray crystallographic studies. The developed synthetic strategy was also explored on a soluble polymer support to incorporate the advantage of rapid synthesis and a high throughput workup process toward the development of a green synthetic protocol for polycyclic alkaloids.
Microwave-Assisted Multicomponent Synthesis of Dihydroquinoxalinones on Soluble Polymer Support
(2015-07-01)
Dalvi, Prashant B.
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Lin, Shu-Fen
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Paike, Vijaykumar
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Sun, Chung-Ming
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應用化學系
A one-pot and two-step reaction of four components, including aldehydes, Fmoc-protected alpha-amino acid, isocyanide, and soluble polymer-supported 4-fluoro-3-amino benzoate ester, was developed for an efficient synthesis of dihydroquinoxalinones under microwave irradiation. Fmoc deprotection followed by intramolecular cyclization of the diamide gave a facile access to novel bicyclic quinoxalin-2-ones. On the basis of this approach, a new route to synthesize this privileged scaffold from the diamide intermediate was designed and accomplished with high yields. Use of multicomponent reaction (MCR) has been shown to display a good functional group tolerance, while the product isolation and purification is straightforward by precipitation and washings. Current library discusses the synthesis and diversification of 21 compounds produced using this strategy.
Rhodium-Catalyzed Regioselective Synthesis of Isocoumarins through Benzothiadiazine-Fused Frameworks
(2016-08-05)
Dalvi, Prashant B.
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Lin, Kuang-Ling
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Kulkarni, Manohar V.
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Sun, Chung-Ming
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應用化學系
An unprecedented two-step, one-pot synthesis of benzimidazothiadiazine 5,5-dioxides is presented. Reaction condition based regioselectivity has been achieved where fused benzimidazo[1,2-b][1,2,4]thiadiazines are exclusively formed under thermal conditions, whereas benzimidazo[2,1-c][1,2,4]thiadiazines were created only under microwave irradiation. The salient features of this protocol include a regioselective sulfonylation of 2-aminobenzimidazole with o-halo sulfonyl chlorides followed by N-C bond formation. The acid forms of these fused regioisomers have been used to introduce novel guanidine containing isocoumarin frameworks.