Glycosides of fatty acids
with a N-acyl link

Lipo-chitooligosaccharides or Nod factors

The close association between symbiotic bacteria (or Rhizobia) and leguminous plants leads to the formation of nitrogen-fixing nodules, conferring on host plants the ability to fix nitrogen. This symbiosis is characterized by a high level of host specificity, mediated by specific recognition of rhizobial molecules called Nod factors (Cullimore JV et al., Trends plant sci 2001, 6, 24).

The structure and the specific functions of these "nodule-inducing principle" (Truchet G et al., Differentiation 1980, 16, 163) were discovered in Rhizobium meliloti (Lerouge P et al., Nature 1990, 344, 781). These are lipo-chitooligosaccharides, based on a backbone of generally four or five N-acetyl glucosamine residues (chitine oligomer) which are N-acylated at the non-reducing end and carry various substitutions which are important determinants of rhizobial host specificity, the terminal non-reducing sugar being N-acylated with a fatty acid of 16 to 18 carbon residues. Different species of Nod factors can be substituted with acetate, sulfate, or carbamoyl groups, or can have different sugars, such as arabinose, mannose, or fucose. The degree of saturation of the acyl chain can also vary from 0 up to 4 double bonds (Perret X et al., Microbiol Mol Biol Rev 2000, 64, 180). 

As the legume-rhizobia symbiosis is established, the plant recognizes Nod factors and initiates transcriptional and developmental changes within the root to allow bacterial invasion and the construction of a novel organ, the nodule. Nod factors thus act as symbiotic signalling molecules for conferring host specificity, for infection, and for nodule development (Hirsch AM et al., Plant Physiol 2001, 127, 1484), and are likely to be perceived by high affinity receptors (Cohn J et al., Trends Plant Sci 1998, 3,105).

Nucleoside fatty amide glycosides

These molecules are formed of a nucleoside linked to glucosamine residues whose one of them is amide linked to a saturated or monounsaturated fatty acid with a normal or branched chain. Many of these glycosides are categorized as antibiotics and have nonspecific antibacterial activities.
The most known class of nucleoside fatty amide glycoside is that of tunicamycin which was identified from Streptomyces lysosuperficus cultures. This polar compound is soluble in DMSO, alkaline water, and hot methanol. A series of tunicamycins was identified having an uracil group and various fatty acid moieties. The general structure is shown below.

Homologue compounds varying at the level of the fatty acid are streptovirudins and corynetoxins.