From Cycloolefins to Linear C2 -Symmetrical 1,4-Diamino-2,3-diol Building Blocks-Peptide Mimetics, Biocatalysis, and Pinacol Coupling of α-Amino Aldehydes

Construction of C-C bonds via photoreductive coupling of ketones and aldehydes in the metal-organic-framework MFM-300(Cr)

Construction of C-C bonds via reductive coupling of aldehydes and ketones is hindered by the highly negative reduction potential of these carbonyl substrates, particularly ketones, and this renders the formation of ketyl radicals extremely endergonic. Here, we report the efficient activation of carbonyl compounds by the formation of specific host-guest interactions in a hydroxyl-decorated porous photocatalyst. MFM-300(Cr) exhibits a band gap of 1.75 eV and shows excellent catalytic activity and stability towards the photoreductive coupling of 30 different aldehydes and ketones to the corresponding 1,2-diols at room temperature. Synchrotron X-ray diffraction and electron paramagnetic resonance spectroscopy confirm the generation of ketyl radicals via confinement within MFM-300(Cr). This protocol removes simultaneously the need for a precious metal-based photocatalyst or for amine-based sacrificial agents for the photochemical synthesis.

Synthesis and biological activity of potent HIV-1 protease inhibitors based on Phe-Pro dihydroxyethylene isosteres

Peptidomimetic inhibitors of HIV-1 PR are still a key resource in the fight against AIDS. Here we describe the synthesis and biological activity of HIV-1 PR inhibitors based on four novel dihydroxyethylene isosteres of the Phe-Pro and Pro-Pro dipeptides. The isosteres, containing four stereogenic centers, were synthesized in high yield and excellent stereoselectivity via the cyclization of epoxy amines derived from α-amino acids. The inhibitors were assembled by coupling the isosteres with suitable flanking groups and were screened against recombinant HIV PR showing activities in the subnanomolar to micromolar range. Two Phe-Pro-based inhibitors active at the nanomolar level were further investigated: both inhibitors combine the ability to suppress HIV-1 replication in infected MT-2 cells with low cytotoxicity against the same cells, thereby displaying a high therapeutic index. These results demonstrate the potential of the new Phe-Pro dihydroxyethylene isostere as a core unit of powerful HIV-1 PR inhibitors.

Regioselective Conversion of the Secondary Hydroxyl Groups ofD-Glucuronic Acid without the Requirement ofO-Protecting Groups

Trifluoromethanesulfonic acid anhydride (triflic acid anhydride) transforms the bicyclic thiazolidinlactam 1 a into the crystalline elimination product 2, in which all four secondary hydroxyl groups of 1 a are differently functionalized. Compound 2 can then add nucleophiles with high chemo- and stereoselectivity. Altogether, the four secondary hydroxyl groups of D-glucuronic acid are selectively transformed without the need for any O-protecting groups. Minimizing the number of O-protecting groups is a prerequisite for the use of sugar scaffolds in molecular libraries. The hapalosin analogues 15, 16, 19, and 22 outline the strategy towards O-diversified glucose derivatives.

Epoxyalcohol route to hydroxyethylene dipeptide isosteres. Stereodivergent synthesis of the diamino alcohol core of ritonavir and its C-2 epimer

A stereoselective synthesis of hydroxyethylene dipeptide isosteres based on the 1,4-diamino-2-hydroxybutane structure is described. Horner-Emmons olefination of phosphonates derived from alpha-amino acids, stereoselective reduction of the resulting enones to allylic alcohols, and syn epoxidation of the latter lead to enantiomerically pure 1-amino-2-hydroxy-3,4-epoxybutanes, key intermediates in the synthesis. Reductive cleavage of the epoxy alcohols with Red-Al proceeds in a highly regioselective way, giving 1-amino-2,4-dihydroxybutanes, from which diamino alcohol hydroxyethylene isosteres are obtained by selective protection of the secondary 2-hydroxy group, via cyclization to 1,3-oxazolidinone, and further elaboration of the 4-hydroxy. Both C-2 epimers of 1,4-diamino-2-hydroxybutanes are accessible by appropriate choice of the conditions for cyclization. The approach is demonstrated by the synthesis of a series of six hydroxyethylene dipeptide isosteres, including the diamino alcohol core of potent HIV-protease inhibitor ritonavir 18 and its C-2 epimer 11a.

Stereoselective synthesis of non symmetric dihydroxyethylene dipeptide isosteres via epoxy alcohols derived from alpha-amino acids

(1R,2R,3S,4S)-4-Amino-3-hydroxy-1,2-epoxybutanes, accessible in four steps from L-aminoesters, react regio- and stereoselectively with diethyl aluminum cyanide to give (1R,2S,3S,4S)-4-amino-2,3-dihydroxynitriles. Hydrolysis yields hydroxylactones equivalent to 2,3-dihydroxy-4-aminoacids. The sequence provides a novel approach to dihydroxyethylene isosteres potentially useful for new HIV-protease inhibitors.