Protecting allyl ester

The Noc group, developed for amino acid protection, is introduced with the acid chloride (Et3N, H2O, dioxane, 2 h, 20°, 61-95% yield). It is cleaved with Pd(Ph3P)4 (THF, A, A -dimethyibarbituric acid, 8 h, 20°, 80% yield). It is not isomerized by Wilkinson s catalyst, thus allowing selective removal of the allyl ester group. 

Silyl-derived linker 36 was prepared in three steps from a silyl ether of serine and incorporated for Fmoc/tBu-based assembly of protected gly-copeptide blocks (Scheme 11) [42]. The a-carboxylic acid function of serine was protected as an allyl ester. Deprotection by a Pd(0) catalyst in the presence of dimedone liberated the carboxylic acid in order for subsequent... 

Synthesis of isomeric chiral protected (63 )-6-amino-hexahydro-2,7-dioxopyrazolo[l,2- ]pyrazole-l-carboxylic acid 280 is shown in Scheme 36. Crude vinyl phosphonate 275, obtained by treatment of diethyl allyloxycarbonylmethyl-phosphonate with acetic anhydride and tetramethyl diaminomethane as a formaldehyde equivalent, was used in the Michael addition to chiral 4-(f-butoxycarbonylamino)pyrazolidin-3-one 272. The Michael addition is run in dichloro-methane followed by addition of f-butyl oxalyl chloride and 2 equiv of Huning s base in the same pot to provide 276 in 58% yield. The allyl ester is deprotected using palladium catalysis to give the corresponding acid 277, which is... 

Synthesis of Characteristic Lipopeptides of Lipid Mode-fied Proteins Employing the Allyl Ester as Protecting Group, T. Schmittberger, A. Cotte, H. Waldmann, Chem Commun 1998, 937-940. 

H Kunz, H Waldmann, C Unverzagt. Allyl ester as temporary protecting group for the (S-carboxy function of aspartic acid. Int J Pept Prot Res 26, 493, 1985. 

Peptide 21, synthesized using the C-terminal enzymatic-cleavable choline ester (Scheme 11), was also synthesized using the C-terminal allyl ester protecting group (Scheme 12). The selective Pd(0)-catalyzed... 

Scheme 15 Synthesis of the doubly palmitoylated heptapeptide corresponding to the C-terminus of hemagglutinin A bearing an N-terminal NBD function using Boc, Aloe, and the allyl ester as protecting groups.

Acylals (geminal diacetates) are frequently used as protecting groups for aldehydes because of their stability to neutral and basic conditions [8]. In addition, the acylal functionality can be converted into other useful functional groups [9]. For example a novel synthesis of chiral allylic esters has been developed using palladium-catalyzed asymmetric allylic alkylation of gem-diesters [10]. The allylation of... 

Scheme 6.90 Chiral N-benzoyl-protected a-amino acid allyl esters obtained from 64- and 78-catalyzed asymmetric DKR of racemic azlactones derived from racemic natural nonnatural a-amino acids.

Scheme 6.91 Typical enantioenriched (R)-oxazinones and (S)-configured N-benzoyl-protected 5-amino acid allyl esters obtained from the 78-catalyzed kinetic resolution of racemic oxazinone mixtures subsequent isolation of the ester through (R)-oxazinone hydrolysis.

Cleavage of the phosphonate allyl esters from Abu[PO(OAl)2]-peptide-resins is accomplished by treatment with Pd(PPh3)4 (50 °C, 5 h)[103l followed by acidolytic deprotection of the Abu[PO(OH)2]-peptide from the resin support. The viability of employing allyl phosphonate protection for phosphopeptide synthesis has been demonstrated by the Fmoc solid-phase synthesis (DIC/HOBt couplings) of several 6-9-mer Abu[PO(OH)2]-containing peptides and has been extended to the synthesis of a 19-mer caldneurin-related Abu[PO(OH)2]-peptide.[104 ... 

Another method for deallylation of allyl esters is the transfer of the allyl group to reactive nucleophiles. Amines such as morpholine are used[415-417], Potassium salts of higher carboxylic acids are used as an accepter of the allyl group[418]. The method is applied to the protection and deprotection of the acid function in rather unstable /3-lactam 664[419,420]. 

The allyl ester [22] can be selectively removed in the presence of Z- [22], Boc- [25,28], or Fmoc amino protection [24]. For example, Fmoc threonine allyl ester 24 was glycosylated with 2-azido-3,4,6-tri-0-acetyl-2-deoxy-a-D-galactopyranosyl bromide 25 [6] to give the conjugate 26 in high yield [24]. Separation of the a-anomer and transformation of its... 

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