6-O-acyl derivatives

The synthetic compound, l,2-di-0-9 -octadecenyl-3-0-/3-D-galactopyranosyl-5n-glycerol, which is an ether analogue of mono-D-galactosyldiacylglycerol, can be converted by plant enzymes into the 6-O-acyl derivative.The availability of the 9-octadecenyl compound can provide a substrate for studies on the direct desaturation of lipid-linked acyl or alkyl chains. 

This procedure was also applied to the synthesis of the closely related 6-O-nocardomycoloyl-MDP (49) (66) and 6 0-corynomycoloyl-MDP (50) 47, 66). In these instances the internal ester (f) was not formed when N,N -dicyclo-hexylcarbodiimide in presence of N-hydroxysuccin-imide was used as coupling reagent (57). Similar 6-O-acyl-derivatives of MDP (51—55) have been synthesized in the same manner, the synthetic fatty acyl group being linear, a-branched and a-branched-P-hydroxyl-ated (57). 

Kusumoto. S., S. Okada, K. Yamamoto, and T. Shiba Synthesis of 6-O-acyl-derivatives of immunoadjuvant active N-acetyl-muramyl-L-alanyl-D-isoglutamine. Bull. Chem. Soc. Japan. 51, 2122 (1978). 

The nature of the intermediates and products formed on oxidation of L-ascorbic acid and its 6-benzoate and 6-palmitate by iodine have been investigated by i C-nmr in both D2O and d6-DMSO. In D2O, there was evidence for the formation of the 3,6-hemiketal-hydrate 63 in equilibrium with the bis-hydrate 64 of dehydroascorbic acid. A similar bis-hydrate was formed from the 6-(9-benzoyl deriv.itive in D2O, and this formed a bis-anhydrodimer on standing. In d -DMSO, the 6-O-acyl derivatives formed the 2,3-dione (dehydroascorbate), which formed the bis-hydrate on adding water. 2 Thg hydrogen-ion dependence in the oxidation of L-ascorbic acid by hexacyanoferrate(III) in aqueous ethanol has been investigated the rate law was derived and the... 

Acylation of -ones and -diones appears to occur mainly at oxygen, but in the fused pyridazino[4,5-6]quinoline (312) the O-acyl derivative (313) was formed via an iV,0-diacyl derivative (72BSF1588). Reduced derivatives, however, are acylated at nitrogen. 

Hodosi, G. Kovac, P., Manipulation of free carbohydrates via stannylene acetals. Preparation of beta-per-O-acyl derivatives of D-mannose, L-rhamnose, 6-0-trityl-D-talose, andD-lyxose. Carbohydr. Res. 1997,303, 239-243. 

Castanosp ermine has been shown to have in vitro antiviral activity against human immunodeficiency virus (HIV) [99] and human cytomegalovirus (CMV) [100], which is an opportunistic pathogen in AIDS. Alterations in viral coat glycoproteins in the presence of castanospermine are associated with a loss of infectivity. 6-0-acyl derivatives of castanospermine are more potent inhibitors of HIV growth than the natural product with the 6-O-butyryl-derivative (MDL 28,374) currently in clinical trials for AIDS. The lipophilic nature of the acyl derivative improves uptake by cells but the compound appears to be intracellularly converted to castanospermine [101]. 

A series of 14-O-acyl derivatives of 17-allyl-, 17-dimethylallyl-, 17-cyclopro-pylmethyl- and 17-cyclobutylmethyl-7,8-dihydronorcodeinones (6-9) (Fig. 1) were patented as safe analgesics with favourable dependence profiles [4]. The pentanoy-loxy and hexanoyloxy derivatives in the 17-cyclopropylmethyl series (8a n - 3,4) had the highest potency in the antiwrithing test in mice. Acylation of the 14-hydroxyl group increased the antinociceptive potency of 3d by two orders of magnitude so that 8a (n = 3,4) were as potent as morphine. 

Dihydro-l,3-4 -oxazines (33) can be formed from O-acyl derivatives of 3-propanolamine even where the formation of smaller rings would also have been possible,123 e.g. ... 

Compounds will be discussed in Sections based on structural analogy, generally related to their biosynthetic ori n. Thus, simple / -terphenyls with a tricyclic C-18 basic skeleton, including their acyclic d-alkyl or O-acyl derivatives are treated in Section 2, normally in order of increasing number of oxygenated functions. Those showing a policyclic C-18 skeleton are discussed in Section 3, while Section 4 includes those possessing an alkylated skeleton (C-19 or more). The main biosynthetic pathways and selected synthetic methods are summarised in Sections 5 and 6, respectively. For the sake of completeness, terphenyls from lichens are shortly reported in Section 2.6. 

Both enantiomers of lactic acid (2-hydroxypropanoic acid) are natural products and easily obtained by biotechnological methods, so there is no need for their synthesis in the laboratory. Even their esters with alkanols, e.g.. 1, are comparatively inexpensive and, therefore, convenient starting materials for derivatization to chiral reagents and auxiliaries. If necessary, such esters can be obtained by any convenient esterification technique. O-Acylated derivatives of lactic esters have been used very successfully as chiral auxiliaries in diastereoselective Diels-Alder reactions (Section D.1.6.1.1.1.1.2.). The acrylate 2 and methacrylate 31-3 and the fu-marate 43 give very high enantiomeric excesses. These are obtained from the lactic ester by treatment with an acid chloride. 

Gomphrenbis. G. I-Viii belongs to the betacyans (see betalains). The name G. encompasses the 6-O-gluco-side (G. 1) and 6 -0-acyl derivatives (esterified with hydroxycinnamic acids, e.g., 4-coumaric and ferulic acids) of betanidin. G. occurs in the flowers of Gom-phrena globosa (Amaranthaceae). G. 1 has also been found in other members of the Caryophyllales where it possibly serves as a precursor of the 6-O-sophoro-side of betanidin (see bougainvilleins). 

The regioselective deacylation of ribonucleosides is mentioned in Chapter 6 equilibration between 3,5- and 2, 5 -di-O-acyl derivatives can be achieved on silica gel allowing the 3, 5-isomer to be obtained as the major product on silica-gel column chromatography. ... 

In vivo labeling experiments showed that label from [ Cjcholesterol appeared in ASG before SG, and it was suggested therefore that the sterol may be glycosylated by a 6-O-acyl glucose derivative (Bush and Grunwald, 1974). No evidence for the acylation of glucose or the postulated final step of ASG synthesis has been obtained. All cell-free systems studied favor the sequence S — SG ASG. 

An example of a successful esterification reaction on industrial scale is shown in Scheme 3.1. 6-0-Acyl derivatives of alkyl glucopyranosides, which are used as fully biodegradable nonionic surfactants in cosmetics [142], were synthesized from fatty acids and the corresponding l-O-aUcyl glucopyranosides under catalysis of thermostable Candida antarctica lipase B in the absence of solvents [137]. In order to drive the reaction towards completion, the water produced during the reaction was evaporated at elevated temperature and reduced pressure (70°C, 0.01 bar). 

The reaction of D-glucose diethyl dhhioacetal with addic acetone fiimished the two diacetonides 6 and 7 in the ratio 3 1 thdr structures which were proposed thirty years ago without proof (P.A.J. Gorin, Can. J. Chem., 1965, 43, 2078) have now been firmly established with the help of extensive n.m.r. spectroscopic analysis. Experimental details fi)r the one-pot preparation of l,2-0-isopropylidene-a-l> xylofiiranose in 80% yield fiom D-xylose have beoi published/ 2, 3 4,6 ,4, 6 -Tri-0-cyclohcxylidene-(X,a -trehalose was an important synthetic precursor of mycobacterial 2,3-di-O-acyl derivatives of oc,a -trehalose in connection with this preparation the lohe 7iidenation, isopropylidenation, and ethylidenation of this disaccharide by use of ethoj rcydohexane, 2-methoxypropene, and acetaldehyde, respectively, in acidic media have been studied in some detail/... 

Sucrose treated with 1,3-bis(2,2-dimethylpropanoyloxy)-l,3-diethyldlborane affords the 4,6-ethylboronate and hence a route to 2,3,1, 3, 4, 6 -hexa-O-acyl derivatives. 

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