The Behavior of 1,4-Benzodiazepine Drugs in Acidic Media, Part XVII. Kinetics and Mechanism of the Acid-Base Equilibrium and the Hydrolysis of Benzodiazepinooxazines.
The automated on-line synthesis of DNA-3'-PNA chimeras 1-4 and (2'-O-methyl-RNA)-3'-PNA chimeras 5-8 is described, in which the 3'-terminal part of the oligonucleotide is linked to the N-terminal part of the PNA via N-(omega-hydroxyalkyl)-N-[(thymin-1-yl)acetyl]glycine units (alkyl = Et, Ph, Bu, and pentyl). By means of UV thermal denaturation, the binding affinities of all chimeras were directly compared by determining their T values in the duplex with complementary DNA and RNA. All investigated DNA-3'-PNA chimeras and (2'-O-methyl-RNA)-3'-PNA chimeras form more-stable duplexes with complementary DNA and RNA than the corresponding unmodified DNA. Interestingly, a N-(3-hydroxypropyl)glycine linker resulted in the highest binding affinity for DNA-3'-PNA chimeras, whereas the (2'-O-methyl-RNA)-3'-PNA chimeras showed optimal binding with the homologous N-(4-hydroxybutyl)glycine linker. The duplexes of (2'-O-methyl-RNA)-3'-PNA chimeras and RNA were significantly more stable than those containing the corresponding DNA-3'-PNA chimeras. Surprisingly, we found that the charged (2'-O-methyl-RNA)-3'-PNA chimera with a N-(4-hydroxybutyl)glycine-based unit at the junction to the PNA part shows the same binding affinity to RNA as uncharged PNA. Potential applications of (2'-O-methyl-RNA)-3'-PNA chimeras include their use as antisense agents acting by a RNase-independent mechanism of action, a prerequisite for antisense-oligonucleotide-mediated correction of aberrant splicing of pre-mRNA.
Hydroxamate based inhibitors of adenylyl cyclase. Part 1: The effect of acyclic linkers on P-site binding
作者:Daniel E Levy、Charles Marlowe、Kim Kane-Maguire、Ming Bao、Diana B Cherbavaz、James E Tomlinson、David M Sedlock、Robert M Scarborough
DOI:10.1016/s0960-894x(02)00653-4
日期:2002.11
The adenylyl cyclases (ACs) are a family of enzymes that are key elements of signal transduction by virtue of their ability to convert ATP to cAMP. The catalytic mechanism of this transformation proceeds through initial binding of ATP to the purine bindingsite (P-site) followed by metal mediated cyclization with loss of pyrophosphate. Crystallographic analysis of ACs with known inhibitors reveals
The Behavior of 1,4-Benzodiazepine Drugs in Acidic Media, Part XVII. Kinetics and Mechanism of the Acid-Base Equilibrium and the Hydrolysis of Benzodiazepinooxazines.
Ring-opening and ring-closing (acid-base equilibrium) reactions of the six-membered oxazine of benzodiazepinoxazines (BZINs) and the subsequent hydrolyses of the diazepine ring have been investigated kinetically and compared with the reactions of benzodiazepinooxazoles (BZOLs) which have the five-membered oxazolidine ring. The ring-closing reaction for BZINs is slower than that for BZOLs due to the increase in the degree of freedom for the moving molety of BZINs. The rates of the ring-opening reactions are almost independent of the substituents at 12b-position (H-(1), CH3-(2), and C6H5-(3)), indicating that an attacking proton may approach equally (non-sterically) to the lone pair of N5 atoms. Possible conformational aspects of BZINs in solution are proposed. Cleavages (hydrolyses) of the diazepine ring occur at the C12b-N5 (iminium) bond for 2 and 3 and are 10-100 times faster than those for the corresponding BZOLs. For 1, in contrast to 2 and 3, hydrolysis of the amide bond (N8-C7) of the diazepine ring takes place instead of the iminium bond, similar to the case of 11b-hydrogen BZOL.