Synthesis of carbasugars

Fig. 28 Application of radical reaction in the synthesis of carbasugar derivatives.

Highly Functionalised Cyclopentanes and Cyclohexanes Synthesis of Carbasugars... 

It was then postulated and soon recognised that carbasugars, by virtue of their close resemblance to parent monosaccharides, could possess interesting biological activities. Therefore, after McCasland s pioneering work, there has been extreme interest in the synthesis of carbasugars and, in particular, of carbapyranoid motifs. 

Johansen, S.K. et al. Synthesis of Carbasugars from Aldonolactones Ritter-Type Epoxide Opening in the Synthesis of Polyhydroxylated Aminocyclopentanes. 2.1 2.4 1999(132]... 

Gomez, A M, Moreno, E, Valverde, S, Lopez, J C, Stereodivergent synthesis of carbasugars from d-mannose. Syntheses of 5a-carba-alpha-D-allose, beta-L-talose, and alpha-L-gulose pentaacetates, Synlett, 891-894, 2002. 

One of the key points in the synthesis of carbasugars is the formation of the scaffolds of the cyclitol moieties, and three types of s)mthetic strategy can be considered ... 

Advances in Chemical Synthesis of Carbasugars and Analogues GLORIA RASSU, LUCIANA AUZZAS, LUIGI PINNA,... 

Other class of polyhydroxylated derivatives acting as sugar mimics consists of carbasugars i.e. sugars in which the ring-oxygen atom is replaced by the carbon atom. Their synthesis can be initiated either from achiral (or racemic) derivatives (this approach will not be dealt with) or more conveniently from simple sugars (chirons). Syntheses of these important compounds were comprehensively reviewed recently.4... 

Monocyclic carbasugars. The 1,3-dipolar cycloaddition was used in the synthesis of polyhydroxylated compound with the seven-membered ring (Fig. 16).29... 

Fig. 16 Application of cycloaddition for the synthesis of 7-membered ring carbasugar derivatives.

Application of simple sugars as starting materials for the preparation of optically pure complex products represents nowadays the classic methodology of organic synthesis it is covered by many comprehensive reviews, cited here only in references.88 These references provide the precise state-of-art in the synthesis of aza sugars, carbasugars and other derivatives. 

Lundt I (2003) Iminosugars, isoiminosugars, and carbasugars from activated carbohydrate lactones efficient synthesis of biologically important compounds. In Witzak ZJ, Tatsuta K (eds) Carbohydrate synthons in natural products chemistry synthesis, functionalization and applications. ACS Symposium Series, vol 841. American Chemical Society, Washington, DC,pp 117-140... 

The intramolecular nitrone cycloaddition (INC) has been used particularly for the synthesis of amino carbasugars [60, 61]. The following scheme illustrates this strategy (Scheme 16) [60], The cycloaddition of nitrone derived from lactol 49 and an excess of N-methylhydroxylamine occurs from the least hindered face affording the isoxazolidine 51 (85% yield). The amino carbasugar 52 was obtained after the cleavage of the N-0 bond. 

Iminosugars, Isoiminosugars, and Carbasugars from Activated Carbohydrate Lactones Efficient Synthesis of Biologically Important Compounds... 

Synthesis of amino/hydroxy substituted cyclopentanes carbasugars... 

In summary, the novel synthesis of (+)-valienamine and (+)-validamine has been accomplished by our synthetic strategies for the constructing of carbasugars. The absolutely stereoselective hydrogenation of 26 and 27 to give (+)-validamine (29) is particularly noteworthy. 

Because of their large amount of chemically different functionalization, trans-CHD are promising precursors especially for the synthesis of, e.g., carbasugars and their analogs with potential biological activity. The simple, but highly functionalized structure of trans-CHD also has a high potential for diversity-oriented syntheses that could lead to a vast variety of different structures in short chemical reaction sequences. 

In this chapter we review recent achievements in the chemical synthesis of pyranoid carbasugars, pointing out relevant biological implications where claimed. 

In the past, ketose-type pyranose carbasugars were mainly investigated in the search for sucrose mimics to employ as non-nutritive sweeteners [25a,b]. Probably due to this seemingly unappealing potential and the inherent difficulties related to their stereoconstitutional features, up until 1990 only one report was found to have been published dealing with the asymmetric synthesis of D- and L-carba-analogues of fructopyranose [34]. 

The synthesis of 6a-carba-p-D-ffuctopyranose (165) (Scheme 26) comprised four key steps, namely the inversion of C4 configuration in quinic ester 160 to obtain 161, the shift of the ketal protection from C5-C6 to C4-C5 to provide 162, the stereocontrolled dihydroxylation of epi-shikimate 162, and the C6-deoxygenation reaction of advanced intermediate 164. Carbasugar 165 was obtained in an overall 12% yield from quinic acid 159 for a 13-step sequence. 

The majority of naturally occurring aminocarbasugars bears the amino functionality located at the pseudoanomeric position however, replacement of one or more hydroxyl groups by amino functions on the carbasugar backbone may offer great opportunities for structural and stereochemical variation. This section is subdivided into three subsections, dealing with the synthesis of validamine, valiolamine, and valienamine-type carbaglycosyl amine structures. 

This last section groups together a number of contributions in the field of carbasugar synthesis which, for reasons of space, could not be dealt with in detail in various sections of the text. For the readers comfort, the publications have been sorted into two tables Table 1 lists reviews and accounts about chemistry and biology of carbasugars and Table 2 enumerates recent reaserch papers focusing on the synthesis of variously-sized carbocyclic carbasugars. 

Dumortier, L. et al. Chemo-Enzymatic Total Synthesis of Some Conduritols, Carbasugars and (+)-Fortamine. 1998 [90]... 

---