Synthese des Proteinphosphatase-2A-Inhibitors (4S,5S,6S,10S,11S,12S)-Cytostatin

Synthesis of a Bioreversibly Masked Lipophilic Adenosine Diphosphate Ribose Derivative

The design of a bioreversibly protected lipophilic sugar nucleotide as a potential membrane-permeable precursor of adenosine diphosphate ribose (ADPR) is described. ADPR is the most potent activator of the transient receptor potential melastatin 2 (TRPM2) ion channel. Membrane-permeable, lipophilic derivatives of ADPR are of great interest as tools for study of the mechanism of TRPM2. The approach described here was based on our recently disclosed "DiPPro" and "TriPPPro" prodrug approaches developed for the intracellular delivery of nucleotides. A lipophilic, bioreversibly masked ADPR analogue containing an enzymatically cleavable 4-pentanoyloxybenzyl (PB) mask at the phosphate moiety next to the 5'-position of adenosine, together with O-acetyl groups, was prepared in high yields. Chemical and enzymatic hydrolysis studies in phosphate buffer (pH 7.3) were performed to assess chemical stability and possible (selective) enzymatic demasking of the ADPR analogue. HPLC-MS revealed that the PB group was readily cleaved enzymatically. In addition, the formation of partially deacetylated ADPR compounds and also of fully unprotected ADPR was observed.

Iterative synthesis of nucleoside oligophosphates with phosphoramidites

P-Amidites can be used in iterative couplings to selectively give mixed P(III) -P(V) anhydrides. These intermediates can be oxidized followed by a rapid removal of the two terminal fluorenylmethyl groups. An iterative synthesis (coupling, oxidation, deprotection) of nucleoside oligophosphates can be carried out in solution and on a solid support. The coupling rates and yields are high, the procedures convenient (non-dry reagents and solvents, ambient conditions, unprotected nucleotides), and the purification is very simple. The method works with all canonical nucleosides and holds promise for significant simplification of the usually cumbersome process of P-anhydride bond construction.

Good timing in total synthesis: the case of phoslactomycin A

The importance for the right order of functional group introduction and manipulation (good timing) was demonstrated in the course of a total synthesis of phoslactomycin A. The synthetic strategy comprised a Cu(I)-thiophene carboxylate (CuTC, Liebeskind's reagent)-mediated coupling to introduce the Z,Z-diene at the final stage of the synthesis in the presence of a protected phosphate. Key features for the assembly of the C1-C13 fragment were an asymmetric dihydroxylation, an Evans-aldol reaction and an advanced protective group strategy. The C14-C21 fragment was accessible via an asymmetric 1,2-addition to cyclohexenone and a subsequent diastereoselective ketone reduction. One crucial task was the dihydroxylation of the C8-C9 alkene, the introduction of the C6-C7 double bond and the generation of the C25-nitrogen functionality. A second example consisted of the best sequence for the generation of the functional groups in the core part (first phosphorylation, second iodo-olefination, third azide/carbamate conversion). The synthetic solutions from this approach are compared with the already existing contributions in the phoslactomycin area.

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.