C-Nitroso-sugar

Naphthalenoid ansamycins with C9 ansa chains consist of two compounds, rubradirin and protorubradirin. These antibiotics possess a C9 ansa chain moiety and a C-nitroso-sugar or a C-nitro-sugar in the structure, respectively. As will be described below, rubradirin appears to be a photooxidation product of protorubradirin. 

The production of free sugars by ozonolysis of the sodium salts of l-deoxy-l-nitro-additols is covered in Chapter 2. A naturally occurring branded-chain C-nitroso-sugar moiety is mentioned in Chapter 19. 

C-NitrosO Sugars such as (40) were obtained as dimers by oxidation (DDQ in CHCy of the corresponding hydroxylamino-sugars. ... 

Less information is available on the occurrence of C-nitroso-compounds in foods. Stable compounds are derivatives in which the nitroso groups are bound to the tertiary carbon. Such a compound is, for example, the nitrosation product 3-deoxy-D-erythro-hexosulose, which is one of the major degradation products of glucose and other sugars (Figure 12.36). 

In crystalline furanose 8.16, the chlorine atom adopts a pseudo-axial orientation and the nitrogen atom, a pseudo-equatorial one. The orientation of the N-O bond is given by the Newman projection along the C-l-N bond, 8.18. A compact model indicates that one face of the N=O bond is very hindered. It is probable that the same conformation exists in solution and that this is what imposes the endo approach as shown in 8.19 in which the cyclohexadiene tries to avoid the sugar support of the nitroso chloro derivative. 

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