Unsubstituted Acetyl Groups

20 Aromatic Ketones Containing Only Acetyl Groups 

Obtained by Fries rearrangement of CH3CO COCH3 4,4 -diacetoxy-diphenylmethane, 

Obtained by hydrolyzing 2-hydroxy-5-(chloro-methyl)acetophenone [5880,5881]. 

20 Aromatic Ketones Containmg Only Acetyl Groups 

---

Unsubstituted Acetyl Groups [5958] p. 1598 l,l -[Methylenebis(2,4-dihydroxy-6-methoxy-3,l-phenylene)]bis-ethanone... 

Equation 8) <1998T11095>, and the (uncatalyzed) reaction of iV-acetyl-2-bromoindol-3-one with these same diamines gives, according to the conditions, either the unsubstituted compounds 32-34 or those in which the acetyl group is retained (Scheme 10) <2001H(55)925>. 

Structure-Activity Relationships. Compounds of the B series were generally more potent than those of the A series. Thus an unsubstituted hydroxy group at the 5-position is activity enhancing (19). Differences in potency between the 1- and 2-series varied among parasites, but in most instances the 1-series was more potent. Reduction of the 22,23-olefin had little effect on activity but further reduction caused a substantial decrease in activity. The monosaccharides were two- to fourfold less active than the parent compounds while the aglycones were more than thirtyfold less active. Table III. Acetylation at the 4 -position caused no change in activity whereas acetylation at the 5- or 23- position caused a considerable decrease in activity. Diacetates and triacetates showed similarly reduced activity. Table IV (20). 

Periodate oxidation of sialic acids had earlier been used for structural determination of O-substituted sialic acids.89 Whereas, for example, one mole of a 4-O-acetylated sialic acid consumes 2 moles of periodate within 10-20 min at 0°, the same amount of the 7-O-acetyl isomer is oxidized by only one mole. As already discussed in connection with the periodic acid-thiobarbituric acid assay, 9-O-substituted sialic acids exhibit a very low rate of oxidation as compared with the unsubstituted sialic acids13 this observation originally led to the erroneous assignment89 of the 9-O-acetyl group to 0-8. All other sialic acids having O-acetyl groups on the side chain are expected to be unaffected by periodate. 

A direct synthesis of a Ni complex of corrin may be carried out thermally when the secocorrin shown in Fig. 24 a (R =CH3, R = formyl or acetyl, R" = CN) is heated in the presence of Ni salts [68, 69]. The corresponding 1-methyl-19-unsubstituted corrinate Ni2+ is then achieved by base-induced removal of the formyl or acetyl group. 

Serotype B contains capsular polysaccharide, 60% of which consists of a (1— 3)-linked a-D-mannopyranosyl main-chain, two of every three units being substituted at 0-2 by /3-D-xylopyranosyl side-chains, the other being disubstituted, at 0-4 with /3-D-xylopyranosyl and at 0-2 with j8-D-glucopyranosyluronic acid units (40). The polysaccharide contains 3 acetyl groups for every 7 sugar residues.169 As serotype C polysaccharide is similar, except for 2 of every 3 units being disubstituted,170 and as serotype D polysaccharide contains 1 of every 3 man-nosyl residues unsubstituted (and no disubstituted residues171), the reclassification appears to be confirmed. 

Partially methylated, acetylated aldononitriles are acyclic derivatives readily formed from reducing sugars by reaction with hydroxylamine in pyridine, followed by the addition of acetic anhydride to effect elimination of acetic acid from oxime acetates and acetylation of unsubstituted hydroxyl groups. These derivatives, although less extensively used, appear to give good GLC separations, and their mass spectra can be readily interpreted without the problem of structural symmetry (75MI3). 

R or R is a phenyl group or when both are methyl groups, the oxygen atom attached to the carbon chain of the hexitol is likely to be more nucleophilic than if an unsubstituted methylene group is present. Further attack by the electrophilic, acylating entity is, therefore, facilitated, and this could result in the replacement of the trifluoroacetoxymethyl substitutuent by an acetyl group. 

Aldehyde 126 was converted to the terminal alkyne (142) in 61% yield by Seyferth-Gilbert homologation (Scheme 23) [60]. These basic conditions were well tolerated and no C-8 epimerization or C-2 deacetylation was observed. Alkyne 142 was coupled with various azides under copper(I)-catalyzed click reaction conditions to afford 1,4-disubstituted-l,2,3-triazoles (143-145) in 88% yield. Similar conditions were used to generate unsubstituted 1,2,3-triazoles. Alkyne 142 was coupled to azidomethyl pivalate under click reaction conditions to give the pivalyl triazole (146) in 88% yield. The pivalyl triazole was then treated with IN NaOH to remove both the pivalyl group and the C-2 acetyl group. These conditions also led to C-8 epimerization. Acetylation of the epimeric mixture under standard conditions (AC2O, pyridine) and preparative scale separation by TLC furnished the C-8 epimeric N-unsubstituted triazoles (147) in 54% yield over three steps in a ratio of 4 6 (C-8 epi-C-8). 

---