Glycerol selective acylation

Miller also explored the ASD of glycerol derivatives through an enantioselective acylation process which relies on the use of a pentapeptide-catalyst which incorporates an A-terminal nucleophilic 3-(l-imidazolyl)-(5)-alanine residue [171], Most recently, Miller has probed in detail the role of dihedral angle restriction within a peptide-based catalyst for ferf-alcohol KR [172], site selective acylation of erythromycin A [173], and site selective catalysis of phenyl thionoformate transfer in polyols to allow regioselective Barton-McCombie deoxygenation [174],... 

A simple approach for lipidation of peptides with di-fatty acid substituted glycerol moieties is based on the use of glyceric acid.119" For this purpose (2i )-glyceric acid is esterified at the two hydroxy groups with fatty acid acyl chlorides and the resulting lipophilic synthon (18) is used directly as an active ester, e.g. Pfp ester, to acylate selected amino groups of peptides, or is used to acylate suitably functionalized spacers. 

A very consistent chracteristic is the selective positioning of the fatty acyl residues on the glycerol backbone. Thus, in a very large percentage of the naturally ocurring phosphatidylcholines, the hydrocarbon chains on the C-l position are highly saturated—hence little or no olefinic bonds are present. On the other hand, when the acyl residues on C-2 are analyzed, well over 95%... 

Regioselective acylations of polyhydroxylated compounds such as carbohydrates, glycerols, steroids, or alkaloids have been carried out with lipases, esterases, and proteases [13, 20]. One example is the Candida antartica lipase (immobilized on acrylic resin) catalyzed monoacylation of the signalling steroid ectysone (1) giving selectively the 2-C)-acetate 2 (eq. (1)). Using vinyl acetate for this transesterification the reaction was irreversibly pushed to the product side, since the liberated enol instantaneously isomerizes to acetaldehyde [21]. The sometimes unfavorable aldehyde is avoided when 1-ethoxyvinyl acetates [22], trichloro- or -fluoroethyl esters [23 a, b], oxime esters [23 c] or thioesters [23 d] are employed for the quasi-irreversible reaction courses. 

Typically, insecticides represent about 30% of the market in agrochemicals. Activity depends on the ability to penetrate insects rapidly and reach sites of action in membranes of nerve cells. Insecticides are more soluble in fats than in water. The aryl amine insecticides include carbamic esters, such as pirimicarb (104), a diazine derivative (Scheme 23). It is of short-to-moderate persistence, but more selective than organophosphorus compounds. Acylation of A-methyl-l-naphthylamine, or reacting the chloroacetamido derivative with potassium fluoride in glycerol, affords the insecticide and acaricide known as nissol (105). 

Lipase-selective esterification has recently helped fractionate PUFA species present in the same mixture. Fish oil-derived FFA was esterified with glycerol using Lipozyme IM in solvent-free media to fractionate DHA and EPA. The unesterified FFA contained 78%o DHA and only 3% EPA, with a 79%o recovery of DHA the esters contained the majority of the EPA and the other acyl groups, with a 91%o recovery of EPA.f Lipases have also successfully fractionated the two most abundant species of CLAs 18 2-9c,llt and 18 2-10t,12c from an equimolar mixture derived from acid-catalyzed isomerization of ALA. ° ... 

In the plastids, acyltransferases provide a direct route for entrance of acyl groups from ACP to membrane lipids. Since this is the standard pathway for phosphatidic acid synthesis in E. coli and cyanobacteria, both the enzymes of phosphatidic acid synthesis in plastids and the glycerolipid backbones they produce are termed prokaryotic . In both chloroplasts and non-green plastids, the glycerol-3-phosphate acyltransferase is a soluble enzyme that, unlike the E. coli enzyme, shows preference for 18 1-ACP over 16 0-ACP. The lysophosphatidic acid acyltransferase, which is a component of the inner envelope of plastids, is extremely selective for 16 0-ACP. The presence of a 16-carbon fatty acid at the... 

In addition, a chiral 1,2-diamine derived from L-proUne was investigated as a catalyst for the KR of primary alcohols with acyl chlorides by Oriyama et al. [50], providing the highest selectivity factors of up to 16 in the case of glycerol derivatives as substrates. Chiral Ph-BOX-Cu(II) complex 17 has also been successfully... 

Thus, the formation of group I-III TAGS can be suggested to involve, in the first place, esterification of rac-l-OH moieties of glycerol yielding 5 different rac-1-components as TAG precursors then, the latter are subjected to a selective sn-1-acylation by H, O, and L to bring about the formation of major mesocarp TAG species. A mesocarp enzyme responsible for the acylation can be supposed to be similar to the lysophosphatidic acid acyltransferase, which... 

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