5 research outputs found
Biomimetic Total Synthesis of Angelicoin A and B via a Palladium-Catalyzed Decarboxylative Prenylation-Aromatization Sequence
Five-step total syntheses of angelicoin A and B from 2,2,6-trimethyl-4-dioxinone are reported using late stage biomimetic aromatization reactions via diketo-dioxinones as intermediates. In addition, with angelicoin A, this aromatization was coupled with a palladium-catalyzed decarboxylative prenylation in a one-pot sequence as the key step
Synthesis of 5âHydroxymethylâ, 5âFormylâ, and 5âCarboxycytidine-triphosphates and Their Incorporation into Oligonucleotides by Polymerase Chain Reaction
The synthesis of the triphosphates of 5-hydroxymethyl-, 5-formyl-, and 5-carboxycytidine and the incorporation of these building blocks into long DNA fragments using the polymerase chain reaction (PCR) are reported. In this way DNA fragments containing multiple hmC, fC, and caC nucleobases are readily accessible
Total Syntheses of Angelicoin A, Hericenone J, and Hericenol A via Migratory Prenyl- and GeranylationâAromatization Sequences
A five-step synthesis of the natural product angelicoin
A using
a late stage highly regioselective palladium(0)-catalyzed decarboxylative
prenyl migration and aromatization sequence as the key step is reported.
The method was extended with geranyl migration in eight-step total
syntheses of hericenone J and hericenol A from geraniol
5âFormyl- and 5âCarboxydeoxycytidines Do Not Cause Accumulation of Harmful Repair Intermediates in Stem Cells
5-Formyl-dC
(fdC) and 5-carboxy-dC (cadC) are newly discovered
bases in the mammalian genome that are supposed to be substrates for
base excision repair (BER) in the framework of active demethylation.
The bases are recognized by the monofunctional thymine DNA glycosylase
(Tdg), which cleaves the glycosidic bond of the bases to give potentially
harmful abasic sites (AP-sites). Because of the turnover of fdC and
cadC during cell state transitions, it is an open question to what
extent such harmful AP-sites may accumulate during these processes.
Here, we report the development of a new reagent that in combination
with mass spectrometry (MS) allows us to quantify the levels of AP-sites.
This combination also allowed the quantification of β-elimination
(βE) products, which are repair intermediates of bifunctional
DNA glycosylases. In combination with feeding of isotopically labeled
nucleosides, we were able to trace the intermediates back to their
original nucleobases. We show that, while the steady-state levels
of fdC and cadC are substantially increased in Tdg-deficient cells,
those of both AP- and βE-sites are unaltered. The levels of
the detected BER intermediates are 1 and 2 orders of magnitude lower
than those of cadC and fdC, respectively. Thus, neither the presence
of fdC nor that of cadC in stem cells leads to the accumulation of
harmful AP- and βE-site intermediates
Deamination, Oxidation, and CâC Bond Cleavage Reactivity of 5âHydroxymethylcytosine, 5âFormylcytosine, and 5âCarboxycytosine
Three new cytosine derived DNA modifications,
5-hydroxymethyl-2â˛-deoxycytidine
(hmdC), 5-formyl-2â˛-deoxycytidine (fdC) and 5-carboxy-2â˛-deoxycytidine
(cadC) were recently discovered in mammalian DNA, particularly in
stem cell DNA. Their function is currently not clear, but it is assumed
that in stem cells they might be intermediates of an active demethylation
process. This process may involve base excision repair, CâC
bond cleaving reactions or deamination of hmdC to 5-hydroxymethyl-2â˛-deoxyuridine
(hmdU). Here we report chemical studies that enlighten the chemical
reactivity of the new cytosine nucleobases. We investigated their
sensitivity toward oxidation and deamination and we studied the CâC
bond cleaving reactivity of hmdC, fdC, and cadC in the absence and
presence of thiols as biologically relevant (organo)Âcatalysts. We
show that hmdC is in comparison to mdC rapidly oxidized to fdC already
in the presence of air. In contrast, deamination reactions were found
to occur only to a minor extent. The CâC bond cleavage reactions
require the presence of high concentration of thiols and are acid
catalyzed. While hmdC dehydroxymethylates very slowly, fdC and especially
cadC react considerably faster to dC. Thiols are active site residues
in many DNA modifiying enzymes indicating that such enzymes could
play a role in an alternative active DNA demethylation mechanism via
deformylation of fdC or decarboxylation of cadC. Quantum-chemical
calculations support the catalytic influence of a thiol on the CâC
bond cleavage