While direct Sonogashira coupling of 6-halopurines with methyl propiolate and with propargyl aldehyde was not successful, the corresponding orthoester and propargyl aldehyde diethylacetal reacted smoothly. Such prepared orthoester was then converted to the desired methylester by methanolysis, the acetal was too stable to be hydrolyzed. The obtained 6-ethynylpurines, bearing orthoester, acetal, methoxycarbonyl and for comparison also the phenyl substituent on the ethynyl group, were subjected to the cycloaddition reaction with cyclopentadiene, diazomethane and phenylazide. Electron deficient alkynylpurines were considerably more reactive in this reaction compared to the not activated phenylethynyl derivative. The prepared alkynylpurines exhibited medium cytostatic activity (IC 50 = 2.6-15 µM), while the cycloadducts were inactive.

A methodology for the synthesis of (E)-6-alkenylpurines, starting from 6-iodopurines, based on a Pd-catalyzed stannation/protodestannation protocol, is described. The alkynylation reactions were catalyzed by Pd(OAc)2/PPh3 in acetonitrile. The Pd-catalyzed stannation itself provided a mixture of Z regioisomers but following protodestannation using TFA induces Z to E isomerization giving (E)-6-alkenylpurines. The reactivity of other 2- and 8-alkynyl purines has also been studied.

in Wiley Online Library (wileyonlinelibrary.com).1,3-Alkadiynyl(trimethyl)silanes were prepared by the Negishi or Sonogashira reactions of bromoethynyl (trimethyl)silane with several terminal alkynes in 34-75% yield. However, the direct Hiyama coupling of these compounds with 6-iodopurine derivatives has not been successful. Therefore, a modified Sonogashira reaction using TBAF or CsF for in situ removal of the trimethylsilyl group has been utilized. This methodology afforded the desired 6-(1,3-butadiynyl)purines in 47-87% yield.

While direct Sonogashira coupling of 6‐halopurines (I) with propargyl aldehyde or methyl propiolate fails, the corresponding diethyl acetal (IIa) and orthoester (IIb) react smoothly.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.