A three-dimensional array for multiparallel synthesis.
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Journal Article↗
Biomedical subjects
Sergey A Kozmin
Publications and source records attributed to Sergey A Kozmin.
Dithiane additions to vinyl epoxides: steric control over the SN2 and SN2' manifolds.
High chemoselectivity can be achieved in the addition of lithium dithiane anions to vinyl epoxides exploiting the steric nature of the dithiane substituent. Unencumbered dithiane anions afford SN2 adducts, whereas sterically encumbered anions lead primarily to SN2' adducts. Furthermore, the SN2' addition occurs syn to the vinyl epoxide.
Alcohols↗
Synthesis of leucascandrolide A via a spontaneous macrolactolization.
We have developed a concise, convergent, and stereocontrolled synthesis of (+/-)-leucascandrolide A (18 steps from commercially available precursors), featuring a complete relay of the initial stereochemical information via a series of diastereoselective transformations. Spontaneous macrolactolization discovered during this synthetic exercise has provided unprecedented access to this macrolide and demonstrated the possibility of accessing even large-ring systems in a highly controlled and efficient manner.
Animals↗
Synthesis of (-)-pinolidoxin: divergent synthetic strategy exploiting a common silacyclic precursor.
[reaction: see text] We describe a highly convergent and efficient synthesis of (-)-pinolidoxin, a potent modulator of plant pathogenesis, providing unambiguous determination of the relative and absolute stereostructure of this highly oxygenated fungal metabolite. Our unique strategy highlights the applications of novel silacyclic precursors for stereocontrolled polyol synthesis and features the finding of the reversible ring-closing metathesis.
Alkenes↗
An efficient approach to Aspidosperma alkaloids via [4 + 2] cycloadditions of aminosiloxydienes: stereocontrolled total synthesis of (+/-)-tabersonine. Gram-scale catalytic asymmetric syntheses of (+)-tabersonine and (+)-16-methoxytabersonine. Asymmetric syntheses of (+)-aspidospermidine and (-)-quebrachamine.
Described is a concise, highly stereocontrolled strategy to the Aspidosperma family of indole alkaloids, one that is readily adapted to the asymmetric synthesis of these compounds. The strategy is demonstrated by the total synthesis of (+/-)-tabersonine (rac-1), proceeding through a 12-step sequence. The basis for this approach was provided by a highly regio- and stereoselective [4 + 2] cycloaddition of 2-ethylacrolein with 1-amino-3-siloxydiene developed in our laboratory. Subsequent elaboration of the initial adduct into the hexahydroquinoline DE ring system was accomplished efficiently by a ring-closing olefin metathesis reaction. A novel ortho nitrophenylation of an enol silyl ether with (o-nitrophenyl)phenyliodonium fluoride was developed to achieve an efficient, regioselective introduction of the requisite indole moiety. The final high-yielding conversion of the ABDE tetracycle into pentacyclic target rac-1 relied on intramolecular indole alkylation and regioselective C-carbomethoxylation. Our approach differs strategically from previous routes and contains built-in flexibility necessary to access many other members of the Aspidosperma family of indole alkaloids. The versatility of the synthetic strategy was illustrated through the asymmetric syntheses of the following Aspidosperma alkaloids: (+)-aspidospermidine, (-)-quebrachamine, (-)-dehydroquebrachamine, (+)-tabersonine, and (+)-16-methoxytabersonine. Of these, (+)-tabersonine and (+)-16-methoxytabersonine were synthesized in greater than 1-g quantities and in enantiomerically enriched form ( approximately 95% ee). The pivotal asymmetry-introducing step was a catalyzed enantioselective Diels-Alder reaction, which proceeded to afford the cycloadducts in up to 95% ee. Significantly, the synthetic sequence was easy to execute and required only four purifications over the 12-step synthetic route.
Alkaloids↗