Levulinoyl

Ethylenedithio)pentanoate Ester (Levulinoyl Dithioacetal Ester) RO-LevS ... 

Another strategy for selective delivery of CA s at cancer cells exploits the intrinsic overexpression of sialic acid in them. Upon incubation of cancer cells with peracetylated N-levulinoylmannosamine the sialoside biosynthetic pathway affords N-levulinoyl sialic acid, the ketone group of which can be a target for an Gd3+ complex of an aminooxy-functionalized DTPA derivative [165]. 

Cycle Used with Glycosyl Phosphate Activation and Levulinoyl Deprotection... 

After developing procedures for the activation and coupling of anomeric trichloroacetimidate and glycosyl phosphate donors as well as for the deprotection of acetyl and levulinoyl esters, we designed a synthesis utilizing all aspects of our automated chemistry. Trisaccharide 24, composed of three... 

Poor yields of ketones were obtained from the reaction of dialkylcuprates with levulinoyl chloride (233), and from pentafluorophenyl-copper and malonyl chloride (115, 180). The yields of the ketones from the reaction of polyhaloarylcopper reagents with succinoyl chloride were also lower than those from a number of other diacid chlorides (101). Acidic hydrogen atoms are the most likely source of trouble in these reactions. 

Abbreviations Ac acetyl AIBN azobisisobutyronitrile All allyl Bn benzyl Bz benzoyl ClAc chloroacetyl DAST diethylaminosulfur trifluoride DBU l,8-diazabicyclo[5.4.0]-undec-7-ene DDQ 2,3-dichloro-5,6-dicyano-/)-benzoquinone DMDO dimethyldioxirane DMTST dimethyl(methylthio)sulfonium trifluoromethanesulfonate Fmoc 9-fluorenyl-methoxycarbonyl HDTC hydrazine dithiocarboxylate IDCP iodonium di-collidine perchlorate Lev levulinoyl MBz 4-methylbenzoyl Me methyl MEK methyl ethyl ketone MP 4-methoxyphenyl NBS iV-bromosuccinimide NIS A-iodosuccinimide Pent n-pentenyl Pfp pentafluorophenyl Ph phenyl Phth phthaloyl Piv pivaloyl PMB 4-methoxybenzyl TBAF tetrabutylammonium fluoride TBDMS tcrt-butyldimethylsilyl TBDPS tert-butyldiphenylsilyl TCA trichloroacetyl TES triethylsilyl Tf trifluoromethanesulfonyl TMS trimethylsilyl Tol 4-methylphenyl Tr trityl Troc 2,2,2-trichloroethoxycarbonyl Ts tosyl. 

The levulinoyl (4-oxopentanoyl) moiety is a very useful temporary protecting group in nucleotide, polysaccharide, and glycolipid s)mthesis. 

The levulinoyl esters are prepared from the free hydroxyl group by treatment of levulinic acid with DCC [255,256] or l-[3-(dimethylamino)propyl]-3-ethylcarbodiimide hydrochloride (EDAC) [257] in the presence of DMAP (O Scheme 38). Additionally, 3 - and 5 -0-levulinyl protected derivatives of 2 -deoxy nucleosides have been prepared by regioselective enzymatic acylation using a variety of lipases and acetonoxime levulinate as acylating agent [258]. In contrast to other ester substituents, the 0-levulinoyl group is far less prone to migration [259]. 

The removal of NSEC carbonates is carried out by reaction with TBAF in the presence of esters including acetyl, levulinoyl, benzoyl and pivaloyl, but also allyl and PMB ethers are not affected. However, the NSEC group cannot be selectively removed in the presence of Fmoc protecting groups. 

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