Deoxynojirimycin

The protonation state of imino-sugar glycosidase inhibitors and that of the catalytic centre to which they bind are central to their action. Imino-sugars such as 1-deoxynojrimycin (1) and isofagomine (2) are widely studied glycosidase inhibitors and it is commonly assumed that these inhibitors interact with the catalytic apparatus in a manner that has been interpreted either as mimicking the oxocarbenium ion-like transition state or simply being adventitious. Whilst the former explanation seems intuitively reasonable, more quantitative analyses, such as the absence of a correlation between k_cat/K_M and 1/K_i for a series of modified substrates and inhibitors, favour the latter interpretation. Regardless, most work assumes that these compounds bind in their protonated forms, but this has only recently been demonstrated through crystallography at “atomic resolution” with a cellobiose-derived form of 2.Here we present the “atomic resolution” structures of the Streptomyces lividans xylanase Xyn10A in complex with xylobiose-derived deoxynojirimycin (3) and isofagomine (4) at both pH 5.8 and 7.5.

Of the piperidine-based azasugars class (Scheme 1), two members, N-butyl-1-deoxynojirimycin (Miglustat, 11)and N-hydroxyethyl-1-deoxynojirimycin (Miglitol, 12; FDA approved), have presently reached the market as drugs against, respectively, Gaucher’s disease (the most common glycosphingolipid lysosomal storage disorder) and type II diabetes (diabetes mellitus). The primary pharmacological activity of Miglustat is inhibition of the enzyme glucosylceramide synthase, catalyzing the first step in the biosynthesis of glycosphingolipids, i.e. the formation of glucosylceramide. Therefore, the treatment of Gaucher’s disease with Miglustat is based on the concept of substrate reduction therapy. In the body Miglustat exhibits a large volume of distribution having the capacity to access organs located deep within, however, itmay only be used in the treatment of type 1 Gaucher patients for whom enzyme replacement therapy is unsuitable. Early studies have shown Miglustat to be also active against the HIV infection. The second commercial drug,Miglitol, is an oral antidiabetic drug which acts by inhibiting alpha-glucosidases (glycoside hydrolysis enzymes), and consequently the ability of the body to breakdown complex carbohydrates into glucose.

The potent and selective inhibition of glycosidases is an important goal for the development of therapeutics. Glycosidases cleave the glycosidic bonds in oligosaccharides and glycoconjugates. Blocking glycosidase activity can aid in the treatment of diabetes, viral infections, lysosomal storage diseases, and cancer. Iminosugars have been shown to be highly effective inhibitors but their limited selectivity can lead to side effects when applied therapeutically. It is clear that improving the selectivity of iminosugars as glycosidase inhibitors is an important goal. The effectiveness of iminosugars as glycosidase inhibitors in many cases depends on their ability to mimic the relevant transition state in the cleavage process. Considering the vast rate enhancements of glycosidases, these enzymes bind the transition state with very high affinity. Consequently, a transition state mimic has the potential to be a very strong inhibitor. The mimicry depends on the complementarity with respect to charge and shape. These issues are intimately linked to the hybridization state of the ‘anomeric carbon’ and the endocyclic oxygen or in the case of derivatives of deoxynojirimycin 1 (Fig. 1) the nitrogen. These atoms should have a considerable sp² character. We here focused on the hybridization aspect by straightforward derivatisation of the nitrogen of deoxynojirimycin 1 to explore new structural motifs for glycosidase inhibition.

Azasugars or iminosugars have significant biological activities and they act as glycosidase inhibitors and are extensively used for the treatment of AIDS, cancer, diabetes and viral infections. The configuration of hydroxyl groups on the piperidine ring has been shown to have different and profound biological activities. Recently, derivatives of 1-deoxynojirimycin (1-DNJ) 1 such as miglitol 2 (ref. 2) and N-butyl-1-deoxynojirimycin 3 (ref. 2) (Fig. 1) have also attracted great deal of attention due to their promising biological activities. Miglitol 2 is approved for non-insulin dependent diabetes treatment and N-butyl-1-deoxynojirimycin 3 for Gauchers disease. However, very less attention has been paid towards the syntheses of other isomers of 1-DNJ 1 such as L-talo-1-deoxynojirimycin (L-talo-1-DNJ) and D-allo-1-deoxynojirimycin (D-allo-1-DNJ).