3.6- Anhydro galactopyranose

Agarose is closely approximated as the alternating copolymer of (1 3)-/3-D-galactopyranose and (l- 4)-3,6-anhydro-a-L-galactopyranose (see formula 5). 

Support for this result was obtained from the taste of 1,5-anhydrohexitols, which, only for purposes of comparison, can be regarded as 1-deoxyal-dopyranoses. 1,5-Anhydro-D-glucitol (that is, the incorrectly named 1-deoxy-D-glucopyranose ) (14), 1,5-anhydro-D-mannitol ( 1-deoxy-D-mannopyranose or 2-deoxy-D-fructopyranose ) (15), and 1,5-anhydro-D-galactitol ( l-deoxy-o-galactopyranose ) (16) are all purely sweet, without any trace of bitterness. Furthermore, the complete absence of bitterness of 1,5-anhydromannitol (16) clearly indicates that the anomeric... 

A satisfactory result was obtained in AgOTf- or NIS/TfOH-activated condensation of S-benzothiazolyl pentofuranosides 93, 94 and 95 with l,2 3,4-di-isopropylidene-a-D-galactopyranose 96 and l,6-anhydro-3,4-isopropylidene-P-D-galactopyranose 97 as the acceptor to afford the corresponding disaccharides in moderate to good yields and stereoselectivity [445],... 

Auch eine direkte Substitution der Mesyl-Gruppe in 2-0-Methansul-fonyl-3,4-0-isopropyliden-l,6-anhydro-p-D-galactopyranose mit KF in... 

Die in der Zuckerchemie iibliche Methode der Substitution einer Mesyloxy-Gruppe unter Waldenscher Umkehr wurde zur Darstellung der 2-Amino-2-desoxy-l,6-anhydro-p-D-gulopyranose aus dem 3-mesylierten Derivat der 2-Acetamido-2-desoxy-l,6-anhydro-p-D-galactopyranose aus-gentitzt... 

Femer wurde 1,6-2,3-Dianhydro-p-D-talopyranose durch alkalische Hydrolyse des Bariumsalzes des l,6-Anhydro-p-D-galactopyranose-2-sulfats gewonnen... 

Aufspaltungen der Epoxide mit Sauren fiihren zu neuen interessanten Derivaten so wurde aus 2-0-p-Toluolsulfonyl-l,6-3,4-dianhydro-p-D-galactopyranose die 2-0-p-Toluolsulfonyl-l,6-anhydro-p-D-glucop)Tanose erhalten Bei gleichzeitiger Anwesenheit von Alkoholen entstehen die entsprechenden 4-0-Alkyl-Derivate 28,32) ... 

C. Bullock, L. Hough, and A. C. Richardson, Rearrangement of a-D-glucopyranose-4-sulphonates to 1,4-anhydro-aP-D-galactopyranose,/. Chem. Soc. Chem. Commun. (1971) 1276-1277. 

Formation of l,2 5,6-di-0-isopropylidene-a-D-n7i( -hexo-furanos-3-ulose (Fig. 2.13, 2.4.2.1 Table 2.3) was one of the first carbohydrate oxidations effected by stoich. RuOyCCl [310, 311]. The reagent was also used for oxidation of 1,6-anhydro-3,4-0-isopropylidene-P-D-galactopyranose to the -P-D-/yxo-hexopyranos-2--ulose, part of a route leading to 1,6-anhydro-P-D-talopyranose (Fig. 2.15) [321]. 

Similarly, various a-D-glucopyranose derivatives having a mesyloxy group at C-4 and an acetoxyl group at C-l are also converted into 1,4-anhydro-/3-D-galactopyranose derivatives on treatment with sodium azide in such aprotic solvents as N,N-dimethylformamide.51 The use of sodium azide in N,N-dimethylformam ide under forcing conditions originated in attempts at nucleophilic displacements to form azido,... 

When l,6-anhydro-y3-D-gaIactofuranose was first obtained from the pyrolysis distillate of D-galactose,58 it was erroneously identified as l,3-anhydro-/3-D-galactopyranose because of its resistance to periodate oxidation, but correct identity was later established.59 Except for these, there appears to be no report of any 1,3-anhydroglycopyranose. Nevertheless, application of the methodology just described leads without undue difficulty to members of this class of compound. 

The first polymerizations reported by Kops and Schuerch147 were those of l,4-anhydro-2,3,6-tri-0-methyl-/3-D-galactopyranose and 1,4-anhydro-2,3-di-0-methyl-a -L-arabinopyranose. The latter compound was slightly contaminated with l,4-anhydro-2,3-di-0-methyl-a-D-xy-lopyranose, but the course of the polymerization could nevertheless be monitored reasonably accurately. For the most part, the polymerizations were conducted at 10% concentration (g/mL) in dichloro-methane, or aromatic hydrocarbons, with 1-5 mol% of phosphorus pentafluoride, or boron trifluoride etherate. At low temperature (—78 to —97°), the d.p. of both polymers produced was —90 at increasing temperatures of polymerization, termination processes became more severe, and the d.p. lower. Usually, the reaction times were long (perhaps unnecessarily so), and the conversions were 50 to 90%. The specific rotations of the D-galactans prepared at —28 and —90° differ by only —10° ( — 85 to — 95°), but those of the L-arabinans varied from + 6... 

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