A short path synthesis of [13C/15N] multilabeled pyrimidine nucleosides starting from glucopyranose nucleosides

The synthesis of fully [13C/15N] labeled pyrimidine nucleosides has been achieved from 13C-glucose and labeled nucleobases. The reaction scheme leads directly to the protected nucleosides without the need for the inversion of configuration of C-3 of 13C-glucose. This was achieved by an oxitative ring-opening reaction removing the carbon with the wrong configuration.     

Reactivity of coordinatively unsaturated iron complexes towards carbon monoxide: to bind or not to bind?

An overview of the reactivity of coordinatively unsaturated iron complexes (in most cases Fe(II)) towards carbon monoxide is presented. Unsaturated iron complexes are known with coordination numbers (CN) of two to five adopting linear or slightly bent (CN = 2), trigonal (CN = 3), tetrahedral, square planar or trigonal pyramidal (CN = 4), and square-pyramidal or trigonal-bipyramidal geometries (CN = 5), respectively. The binding of CO depends strongly on the number and the nature of co-ligands (overall ligand field strength), the charge of the complex, the complex geometry, and the spin state of the unsaturated metal center. In many cases, CO addition to high-spin iron complexes takes place with concomitant spin state changes forming compounds in the lowest possible spin state, i.e., with S = 0. In several other cases, however, the addition of CO is reversible or is even totally rejected altogether for either thermodynamic or kinetic reasons. In the case of the latter such reactions are termed "spin-blocked" or "spin forbidden".     

New Types of Very Efficient Photolabile Protecting Groups Based upon the [2‐(2‐Nitrophenyl)propoxy]carbonyl (NPPOC) Moiety

Based upon the photolabile [2‐(2‐nitrophenyl)propoxy]carbonyl group (NPPOC), a large number of modified 2‐(2‐nitrophenyl)propanol derivatives substituted at the phenyl ring (see 23 – 34 and 57 – 76 ) as well as at the side‐chain (see 85 – 92 and 95 – 98 ) were synthesized to improve the photoreactivity of this new type of photolabile entity. The phenyl moiety was also exchanged by the naphthalenyl group (see 102, 103, 105, 108, 110, 113 , and 114 ), the thienyl substituent (see 115, 117, 118 , and 120 ), and the benzothienyl substituent (see 121 ). The 2‐(2‐nitroaryl‐ and heteroaryl)propanols were converted with diphosgene into the corresponding carbonochloridates, which reacted subsequently with thymidine to the thymidine 5′‐(protected carbonates) 123 – 178 as the main reaction products. In several cases, the corresponding 3′‐carbonates and 3′,5′‐dicarbonates 179 – 212 were also isolated and characterized. Photolysis studies under standardized conditions (see Table) indicated that the rate of photocleavage varies in a broad range depending on the substituents. So far, the thymidine 5′‐[2‐(5‐halo‐2‐nitrophenyl)propyl carbonates] 127 – 129 , 5′‐[2‐(nitro[1,1′‐biphenyl]3‐yl)propyl carbonates] 136 – 139 , 5′‐{2‐[2‐nitro‐5‐(thianthren‐1‐yl)phenyl]propyl carbonate} ( 140 ), 5′‐[2‐(5‐naphthalenyl‐2‐nitrophenyl)propyl carbonates] 141 and 142 , and 5′‐[2‐(2‐nitro‐5‐thienylphenyl)propyl carbonates] 143 and 144 showed the best properties regarding fast and uniform deprotection. Since the nucleobases of 213 – 215 do not influence the photocleavage features, in general, the new type of photolabile building blocks allows in form of their 3′‐phosphoramidites the photolithographic formation of high‐quality biochips.