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J Am Chem Soc ; 142(8): 4061-4069, 2020 02 26.
Artigo em Inglês | MEDLINE | ID: mdl-32013410


We report a new method for stereoselective O-furanosylation reactions promoted by a precisely tailored bis-thiourea hydrogen-bond-donor catalyst. Furanosyl donors outfitted with an anomeric dialkylphosphate leaving group undergo substitution with high anomeric selectivity, providing access to the challenging 1,2-cis substitution pattern with a range of alcohol acceptors. A variety of stereochemically distinct, benzyl-protected glycosyl donors were engaged successfully as substrates. Mechanistic studies support a stereospecific mechanism in which rate-determining substitution occurs from a catalyst-donor resting-state complex.

Furanos/química , Tioureia/química , Catálise , Ligação de Hidrogênio , Estereoisomerismo
J Org Chem ; 82(24): 13500-13516, 2017 12 15.
Artigo em Inglês | MEDLINE | ID: mdl-29171266


A unified synthetic strategy toward the oridamycin and xiamycin families of natural products was designed, aiming to access several natural products from a common synthetic intermediate readily prepared from geranyl acetate. Part of this strategy was successfully realized, culminating in the synthesis of oridamycin A and oridamycin B. Key steps include a Mn(III)-mediated oxidative radical cyclization to construct the trans-decalin ring, and a 6π-electrocyclization/aromatization sequence to produce the 2,3-fused carbazole. Oridamycin B was accessed through a late-stage, C-H oxidation that converted the C16 methyl to a hydroxymethyl. A variety of strategies were explored to form a chelated radical intermediate en route to xiamycin A, including enolate SET oxidation, oxo-vanadium oxidation, and atom-transfer cyclization. Unfortunately, none of these strategies provided the desired C16-epimeric trans-decalin. Exploratory studies on photoredox-catalyzed radical cyclizations yielded interesting results, including the formation of a bicyclic lactone arising from oxidative termination of the photoredox-catalyzed radical cyclization, and a double 6-endo cyclization with catalyst loadings as low as 0.01 mol%.

Indóis/química , Sesquiterpenos/química , Estrutura Molecular , Sesquiterpenos/síntese química
Org Lett ; 17(13): 3358-61, 2015 Jul 02.
Artigo em Inglês | MEDLINE | ID: mdl-26069989


The total synthesis of both oridamycin A and oridamycin B was accomplished starting from a common synthetic intermediate readily prepared from geranyl acetate. The sequence utilizes an oxidative radical cyclization to construct the trans-decalin ring system, setting three of four contiguous stereocenters in one operation. The carbazole nucleus was forged through a one-pot process entailing acid-promoted dehydration followed by 6π-electrocyclization/aromatization.

Sesquiterpenos/síntese química , Acetatos/química , Monoterpenos Acíclicos , Ciclização , Estrutura Molecular , Oxirredução , Sesquiterpenos/química , Estereoisomerismo , Streptomyces/química , Terpenos/química
J Am Chem Soc ; 136(27): 9743-53, 2014 Jul 09.
Artigo em Inglês | MEDLINE | ID: mdl-24959981


Although dimeric natural products can often be synthesized in the laboratory by directly merging advanced monomers, these approaches sometimes fail, leading instead to non-natural architectures via incorrect unions. Such a situation arose during our studies of the coccinellid alkaloids, when attempts to directly dimerize Nature's presumed monomeric precursors in a putative biomimetic sequence afforded only a non-natural analogue through improper regiocontrol. Herein, we outline a unique strategy for dimer formation that obviates these difficulties, one which rapidly constructs the coccinellid dimers psylloborine A and isopsylloborine A through a terminating sequence of two reaction cascades that generate five bonds, five rings, and four stereocenters. In addition, a common synthetic intermediate is identified which allows for the rapid, asymmetric formal or complete total syntheses of eight monomeric members of the class.

Alcaloides/síntese química , Materiais Biomiméticos/química , Alcaloides/química , Dimerização , Conformação Molecular
Org Biomol Chem ; 10(12): 2373-6, 2012 Mar 28.
Artigo em Inglês | MEDLINE | ID: mdl-22261792


The application of the safety-catch linker concept to solid-phase glycoconjugate synthesis is described. The process allows for direct conjugation of resin bound glycans to complex aglycones during cleavage. Large excesses of either coupling partner are not required, and even very hindered alcohols serve as acceptors in the reaction.

Tioglicosídeos/química , Álcoois/química , Dissacarídeos/química , Glicosilação , Estrutura Molecular