Towards the combinatorial synthesis of spongistatin fragment libraries by using asymmetric aldol reactions on solid support

Short Scalable Route to Bis-morpholine Spiroacetals and Oxazepane Analogues: Useful 3D-Scaffolds for Compound Library Assembly

sp3-Rich molecular scaffolds incorporating nitrogen heterocycles represent important starting points for assembling compound screening libraries and drug discovery. Herein, we report a four-step synthesis of a conformationally well-defined sp3-rich scaffold incorporating two morpholine rings embedded within a spiroacetal framework. The synthesis involves the intermediacy of a 2-chloromethyl-substituted morpholine, accessed from epichlorohydrin and readily available β-aminoalcohols. Base-mediated dehydrochlorination affords an exocyclic enol ether, from which the second morpholine ring is constructed in two steps. Scaffold synthesis is high-yielding and can be performed on a large scale. The methodology allows ready substitution of one-or both- of the morpholine rings for 1,4-oxazepanes and the generation of 6,7- and 7,7-spiroacetal analogues, which are virtually unexplored in drug discovery. Substituted 6,6-systems can be prepared and, in some instances, undergo acid-mediated anomerization to deliver the scaffolds in high diastereoselectivity. The two amine functionalities embedded in the 6,6- and 6,7-spiroacetal scaffolds were sequentially functionalized to provide a diverse physical compound library. These library compounds occupy a similar chemical space to small-molecule drugs that have been approved for clinical application by the Food and Drug Administration yet are structurally dissimilar and may therefore act upon novel targets, representing attractive starting materials for drug discovery.

Photochemical Alkene Isomerization for the Synthesis of Polysubstituted Furans and Pyrroles under Neutral Conditions

A photochemical approach to polysubstituted heterocycles using UV-induced alkene isomerization is described. The method allows for the synthesis of disubstituted furans and pyrroles under mild and neutral conditions and also provides access to a class of trisubstituted furans pertinent to natural-product synthesis. The method has broad functional-group tolerance and many richly decorated heterocycles have been prepared incorporating functional groups that are unstable under Brønsted and Lewis acidic conditions.

Didecarboxylative Iron-Catalyzed Bidirectional Aldolization towards Diversity-Oriented Ketodiol Synthesis

1,3-Acetonedicarboxylic acid was selectively activated by Fe(acac)3 , providing a synthetic platform for rapid synthesis of keto-3,3'-diols. The bidirectional aldol reaction was efficient for challenging aliphatic aldehydes, providing a rapid route to potentially bioactive complex structures.

Possibilities of quercetin insertion into poly(N,N-dimethylacrylamide-co-3, 9-divinyl-2, 4, 8, 10-tetraoxaspiro (5.5) undecane) network

The study presents the possibility of coupling quercetin into poly(N,N-dimethylacrylamide-co-3, 9-divinyl-2, 4, 8, 10-tetraoxaspiro (5.5) undecane) (PDMA-co-U) gel network through a semi-imprinted procedure in order to obtain a responsive antioxidant composite. A continuous magnetic field was used during quercetin insertion for prearranging the compounds - macromolecular matrix and quercetin - and improving the coupling efficiency of the flavonoid structure into the polymeric network. The new supramolecular systems were characterized by FTIR, SEM and thermogravimetric analyses. The dependence of the swelling degree equilibrium and particle size distribution of the studied chemical structures were also evaluated related to the experimental conditions of preparation.

Evaluation of the controlled release ability from the poly(2-hydroxyethyl methacrylate-co-3,9-divinyl-2,4,8,10-tetraoxaspiro[5.5]-undecane) polymer network synthesized in the presence of β-cyclodextrin

The study presents the possibility to use the 2-hydroxyethyl methacrylate--HEMA copolymer with a comonomer with spiroacetal moiety, 3,9-divinyl-2,4,8,10-tetraoxaspiro[5.5]-undecane)-U, as polymer network for loading the indomethacin--INN as drug model, and also, the controlled release evaluation of the prepared bioactive system. The macromolecular compounds were prepared by radical dispersion polymerization in the presence of a pair of surfactants. The use of cyclodextrin as surfactant allowed the building of the host-guest complexes by inclusion of hydrophobic molecules. Also, the cyclodextrin supplemented the hydrogen bonds and the hydrophobic interactions responsible for the stability of the achieved complexes. The copolymers composition and the INN inclusion onto the polymeric matrix were confirmed by FTIR analysis. The porous structure of the lyophilized P(HEMA-U) samples was illustrated by SEM images. The swelling studies evidenced the interdependence between P(HEMA-U) network properties and the spiroacetal moiety amount. Thus, the copolymers presented the increase of the equilibrium swelling degree with pH and temperature. Also, the polymeric matrices manifested dual sensitivity with pH and temperature. The in vitro release of the INN drug from the polymeric network as well as the in vivo experimental studies evidenced the benefit consequence of the spiroacetal compound presence. The clinical observation of the experimental groups does not show any behavioral modifications to suggest a possible toxic effect of these polymeric formulations with and without INN.

Synthesis of natural product inspired compound collections

Natural products, their derivatives, and their analogues are among the most important sources for new drug candidates and tools for chemical biology and medicinal chemistry research. Therefore, there is a need for the development of efficient synthesis methods which give access to natural product derived and inspired compound collections. To meet this challenge, the requirements of multistep stereoselective syntheses, and the logic and methodology of natural product total synthesis need to be translated and adapted to the methods and formats for the synthesis of compound collections. Recent developments in the synthesis of natural product inspired compound collections having carbocyclic and heterocyclic scaffolds highlight the fact that this goal can be successfully attained. The progress made has paved the way for the integration of natural product inspired compound collections into medicinal chemistry and chemical biology research.

Spiroketals via oxidative rearrangement of enol ethers

Oxidative rearrangement of cyclic enol ethers leads to alpha-alkoxyesters. In the presence of a neighboring spiroether, this approach provides a stereoselective access to spiroketals. A modified proposal for the biosynthesis of acutumine is presented.

Enantio- and Diastereoselective Allylmetalations: An Easy and Efficient Access to the AB Spiroketal of Spongistatin

[reaction: see text] A unique combination of highly enantio- and diastereoselective allylmetalations and a one-pot "desacetalization/spiroketalization" have been employed to synthesize the AB spiroketal fragment (C1-C13) of spongistatin in 15 steps and in excellent diastereoselectivity.

Chemical variation of natural product-like scaffolds: design and synthesis of spiroketal derivatives

The design and synthesis of spiroketal structures and their chemical modification, leading to a collection of new small molecules for biological evaluation as orally-bioavailable lead compounds is described. Both [6,5]- and [6,6]-membered ring spiroketal units have been prepared in a stereochemically-varying fashion starting from commercially available (R)- or (S)-glycidol, in ten, eleven and twelve linear steps, in overall yields of 45, 40 and 20%, respectively. Further elaboration according to Lipinski's guidelines has given a collection of structurally-diverse, new spiroketal derivatives in high yields and with high purity.

Enantioselective synthesis on the solid phase

Organic transformations on substrates which are immobilized on an insoluble, polymeric carrier have found broad application in compound collection synthesis. In contrast to other synthetic methodologies in solid-phase organic synthesis, reactions that afford non-racemic products are strikingly under-represented. Not only does the introduction of stereoinformation on immobilized, achiral starting materials provide enantioenriched products which can be of value for biological testing, but it also opens up new perspectives for accessible structures. This feature article gives an overview of successful enantioselective transformations on a solid support. Critical differences in the corresponding solution-phase protocols are highlighted, and applications to the generation of compound collections are particularly mentioned.

Solid phase synthesis of a spiro[5.5]ketal library

A spiro[5.5]ketal library embodying the core structure of numerous biologically active natural products was synthesized employing a double intramolecular hetero Michael reaction as a key transformation.