Beitr?ge zur Harnanalyse

Ohne Zusammenfassung     

Disodium tetrakis(hexanoato‐O)zinc(II)

The structure of the title compound, Na₂[Zn(C₆H₁₁O₂)₄], consists of two‐dimensional polymeric sheets. The Zn²⁺ ions are approximately tetrahedrally coordinated by O atoms from different hexanoate anions. Both Na⁺ ions are six‐coordinated by carboxyl­ate O atoms. One of the hexanoate O atoms is attached to one Zn²⁺ ion and one Na⁺ ion, and the remaining O atom is attached to two Na⁺ ions.     

Addition Reactions of Glycal Esters: Access to Glycosyl Donors of Kdo,d-glycero-d-talo- and d-glycero-d-galacto-2-Octulosonic Acid Residues

ABSTRACT

Addition reactions of O-acetylated glycal esters of Kdo mono-, α-(2→8)- and α-(2→4)- linked Kdo disaccharide derivatives 1a - c with NIS in acetic acid afforded good yields of trans-diaxial as well as minor amounts of trans-diequatorial and cis-configured 2-O-acetyl-3-deoxy-3-iodo derivatives, which were efficiently reduced with Bu₃SnH/AIBN to give the corresponding per-O-acetylated Kdo methyl ester derivatives. Similar reactions of 1a with NBS or NCS furnished the trans-diaxial 2-O-acetyl-3-bromo-3-deoxy- as well as 3-chloro-3-deoxy derivatives as the main products. Reaction of 1a with NBS in aqueous MeCN provided the 2,3-trans-bromohydrin derivative 11c, which upon treatment with DBU in MeCN gave the elimination product 11 and the α-2,3-anhydro derivative 12 as a suitable donor of glycosides with D-glycero-D-talo- or D-glycero-D-galacto configuration, respectively.     

Stereoselective Formation of Triphenylene Ketals

The oxidative trimerization of catechol ketals by MoCl₅ or MoCl₅/TiCl₄ mixtures leads preferentially to the all‐syn stereoisomer of the corresponding triphenylene ketal. The concomitant metal salts of the oxidative coupling most probably form a multinuclear template that directs the diastereoselectivity in a subsequent isomerization step under electrophilic conditions. Several functionalities can serve as coordination sites for the multinuclear metal chloro clusters. Suitable functional groups have to be stable towards the strong electrophilic and oxidizing conditions. Therefore, esters, nitriles, nitro derivatives, triazoles, and pyridines are successfully employed. Based on the flexibility and size of the substrate, different reagent mixtures lead to the stereoselective formation of the all‐syn derivatives.     

Construction of a New Class of Tetracycline Lead Structures with Potent Antibacterial Activity through Biosynthetic Engineering

Antimicrobial resistance and the shortage of novel antibiotics have led to an urgent need for new antibacterial drug leads. Several existing natural product scaffolds (including chelocardins) have not been developed because their suboptimal pharmacological properties could not be addressed at the time. It is demonstrated here that reviving such compounds through the application of biosynthetic engineering can deliver novel drug candidates. Through a rational approach, the carboxamido moiety of tetracyclines (an important structural feature for their bioactivity) was introduced into the chelocardins, which are atypical tetracyclines with an unknown mode of action. A broad‐spectrum antibiotic lead was generated with significantly improved activity, including against all Gram‐negative pathogens of the ESKAPE panel. Since the lead structure is also amenable to further chemical modification, it is a platform for further development through medicinal chemistry and genetic engineering.