RESUMEN
A highly selective convergent coupling reaction is described between alkynes for the synthesis of stereodefined trisubstituted (E,E)-1,3-dienes-structural motifs commonly found embedded in the skeletons of bioactive polyketide-derived natural products. While numerous multistep processes for the synthesis of this stereodefined functional group exist, the current method represents a significant advance as it does not require stereodefined olefinic coupling partners (vinyl halide or vinyl organometallic); it proceeds by a single convergent C-C bond-forming event (avoiding multistep methods based on carbonyl olefination) and is tolerant of a diverse array of functional groups including free hydroxyls. Through a systematic study of titanium-mediated reductive cross-coupling reactions of internal alkynes with terminal alkynes, a fragment coupling reaction of great utility in natural product synthesis has emerged. Here, use of a proximal hydroxy group to control regioselection in the functionalization of a preformed titanacyclopropene has led to the establishment of a highly selective bimolecular coupling process, where C-C bond formation occurs in concert with the establishment of two stereodefined alkenes. Compared to the body of literature known for related metal-mediated coupling reactions, the current work defines a powerful advance, achieving site-selective bimolecular C-C bond formation without the need for using TMS-alkynes or conjugated alkynes. Overall, complex 1,3-dienes relevant for the synthesis of polyketide-derived natural products of varying stereochemistry were prepared with typically >or=20:1 selectivity, defining the important role of an alkoxide directing group located delta to preformed titanacyclopropenes.
Asunto(s)
Alcadienos/síntesis química , Factores Biológicos/síntesis química , Alcadienos/química , Alquinos/química , Factores Biológicos/química , Estructura Molecular , EstereoisomerismoRESUMEN
Titanium-mediated cross-coupling of allenic alcohols with alkynes has been investigated. Divergent reaction pathways were discovered that provide either stereodefined 1,4-dienes or substituted cross-conjugated trienes. In short, allene substitution plays a critical role in the determination of reaction pathway.
RESUMEN
We describe a titanium-mediated reaction for the convergent coupling of allenic alcohols with aromatic imines. Overall, the bond formation occurs at the central carbon of the allene, proceeds with net allylic transposition, and provides substituted 1,3-dienes bearing allylic amine functionality in a regio- and stereoselective fashion.
RESUMEN
A titanium alkoxide-mediated convergent coupling between internal alkynes and allenes is described for the regio- and stereocontrolled synthesis of substituted acyclic 1,4-dienes.
Asunto(s)
Alcoholes/química , Alcadienos/química , Alquinos/química , Polienos/síntesis química , Alcoholes/síntesis química , Estereoisomerismo , Titanio/químicaRESUMEN
Previous reports from our laboratories described potent tripeptide thrombin inhibitors which incorporate heterocycle-substituted chlorophenyl groups in the P1 position. Using these as lead compounds for further optimization, we identified sites of metabolism and designed analogs with 4-fluoroproline in P2 and cyclopropane-containing side chains in P3 as an approach to reducing metabolism and improving their oral pharmacokinetic performance. The large (300-fold) difference in potency between analogs containing (4R)- and (4S)-4-fluoroproline was rationalized by analyzing inhibitor-enzyme interactions in crystal structures of related compounds and by molecular modeling which indicated that the more potent (4R)-4-fluoroproline isomer stabilizes a proline ring conformation that is preferred for binding to the enzyme. An optimal compound from this work, 41, exhibits high potency in a coagulation assay in human plasma (2xAPTT=190 nM), excellent selectivity versus the digestive enzyme trypsin (K(i)=3300 nM), and excellent oral bioavailability in dogs with moderate clearance (F=100%, CL=12 mL/min/kg).
Asunto(s)
Inhibidores Enzimáticos/farmacología , Prolina/análogos & derivados , Trombina/antagonistas & inhibidores , Sitios de Unión , Inhibidores Enzimáticos/síntesis química , Inhibidores Enzimáticos/química , Humanos , Técnicas In Vitro , Modelos Moleculares , Conformación Molecular , Prolina/química , Conformación Proteica , Estructura Terciaria de Proteína , Estereoisomerismo , Relación Estructura-Actividad , Trombina/metabolismo , Tripsina/efectos de los fármacos , Tripsina/metabolismoRESUMEN
[reaction: see text] A convergent Group 4 metal-mediated coupling process is described for the synthesis of polypropionate-derived (E,E)-1,3-dienes. Both the stereochemistry of the internal alkyne and the presence/absence of a tethered alkoxide on this pi-component were found to play critical roles in dictating the regiochemical course of these reactions.