The C-nucleoside 2'-deoxypseudouridine, in contrast to dU, forms stable C:pseudoU-A triplets. 2-Aminopurine lacks groups critical for hydrogen bonding and is a mildly fluorescent base.
Demand for sulfur modified bases continues to expand for investigations of oligonucleotide structure, but primarily for cross-linking purposes. 6-Thio-dG, 4-Thio-dT and 4-thio-dU are very useful modifications for photo cross-linking and photoaffinity labelling experiments. Oligos containing 2-thio-dT are useful in examining protein-DNA interaction by acting as photosensitizing probes. The thiocarbonyl group in 2-thio-dT is especially interesting in that it is available to react with compounds associating with the minor groove of DNA. 2-Amino-A forms a very stable base pair with T containing three hydrogen bonds but the stability of the base pair with 2-thio-T is greatly diminished. Due to steric interactions between the 2-thio group of thymidine and the 2-amino group of 2-amino-A, the base pair contains only a single hydrogen bond. Oligos containing 2-amino-dA and 2-thio-dT exhibit high affinity for natural oligonucleotides but show little affinity for other similar oligos even of a complementary sequence.
Coupling: Standard coupling time. Use 0.02 M Iodine for Oxidation.
Deprotection: Deprotect with1.0M DBU in anhydrous acetonitrile at Room Temperature for 2hrs to remove the cyanoethyl protection. Complete the deprotection with 50mM NaSH in concentrated NH4OH at Room Temperature for 24hrs.
4-thioU is efficiently activated for crosslinking by exposure to long-wavelength UV light for up to 10 minutes. Crosslinks are formed with RNA and proteins.Oligonucleotides containing 4-thiodU (10-1051) and 4-thioT (10-1033) can be produced from the triazole modified phosphoramidites using the convertible nucleoside strategy (1,2). However, we now offer the nuclesides 4-thio-dT (10-1034), 4-thio-dU (10-1052), 2-thio-dT (10-1036), and 4-thio-U (10-3052) for direct incorporation into oligonucleotides and the convertible monomers have been discontinued. A further enhancement of this strategy used 4-thioxU as an intermediated in the preparation of thiocarbonyl crosslinkers (3).||REFERENCE(S):(1) Y.Z. Xu, Q. Zheng, and P.F. Swann, J. Org. Chem., 1992, 57, 3841., (2) The Glen Report, 1993, 6.1, 1, and references cited therein., (3) R.S. Coleman and J.M. Siedlecki, Journal of the American Chemical Society, 1992, 114, 9229-9230.