An optimally capped duplex DNA (sigma-DNA) was synthesized in which the cytosines in the homopyrimidine strand of sigma-DNA 1 were replaced by 5-methylcytosine leading to sigma-DNA 2. Although only involving 13 base pairs, this modification resulted in very high melting temperatures above 90 degrees. In addition, sigma-DNA 2 was able to form triple helices with the corresponding homopyrimidine DNA or RNA even at neutral pH. This opens up the possibility to use sigma-DNA in a triple-helix approach to modulate gene expressions on the level of the translation process.

Two optimally capped duplex DNA molecules (sigma-DNA; see I and 4) were synthesized and their utility demonstrated for triplex investigations with their corresponding homopyrimidine DNA and RNA single strands in the D . (D . D) and R . (D . D) Hoogsteen mode. Furthermore, it was established that sigma-DNA is an ideal tool to study the pH dependency of tripler formation.

We report a solid-phase synthesis of 3-acyltetramic acids that are components of naturally occurring antibiotics. The products were obtained in satisfactory purity by a novel cyclization-cleavage strategy via a Dieckmann condensation.

We describe the synthesis of short double-stranded DNA fragments (see 4 and 13) which are capped on both ends by an optimally designed linker molecule. The new structures are stable with respect to hybrid dissociation and should have implications in physical studies involving double-stranded DNA as well as in the antisense area for the specific modulation of gene expressions.