Antibiotics, branched-chain deoxy sugars

More than a dozen branched-chain, deoxy sugars have now been discovered as components of antibiotics. One review on their biosynthesis4 and two5,6 on the chemistry and biochemistry of branched-chain sugars have appeared. These sugars can be divided into two groups according to their biosynthesis. 

Branched-chain deoxy-sugars have been characterised in more recent years as a result of extensive studies on the antibiotics synthesised by microorganisms. Streptose (p. 25), a constituent of streptomycin, was the first branched-chain sugar synthesised by a micro-organism to be identified. Cordycepose 3-deoxyapiose) (LXIX), mycarose (2,6-dideoxy-3-C-methyl-... 

D-Apiose can be isolated from parsley and is a component of the cell wall polysaccharide of various marine plants. Among its novel structural features is the presence of only a single chirality center. L-Vancosamine is but one portion of vancomycin, a powerful antibiotic that has emerged as one of only a few antibiotics that are effective against drug-resistant bacteria. L-Vancosamine is not only a branched-chain carbohydrate, it is a deoxy sugar and an amino sugar as well. 

During the past nine years the subject of total synthesis of sugars and cyclitols has been vividly developed. The discovery of a large number of unusual sugars in nature—deoxy, amino, branched chain sugars (many of them components of antibiotics)—made their synthesis attractive. On the other hand, improvements in organic reagents and synthetic methods allowed a return to older preparations which could be now better performed. Finally, some synthetic ideas already described in this series, in the first chapter of the volume on the total synthesis of carbohydrates, are further expanded. 

Another new anti-tumour antibiotic, virenomycin A, has the branched-chain sugar 6-deoxy-3-C-methyl-D-gulopyranoside (37) -linked as a C-glycoside to the same aglycone present in gilvocarcin V and ravidomycin (see Vol.17,p.181,182). 

The 3, 5-iV-formylepimine derivative (432) [derived from the diacetal (431)] has been converted into a protected analogue (433) of the polyoxin antibiotics. The stereochemistry of the AT-formylepimine derivative (432) was established by A -ray crystallographic analysis. A series of lipophilic 9-(3-alkyl-3-deoxy-j8-D-ribofuranosyl)adenines (434) has been prepared by glycosylation of 6-benzamido-9-chloromercuripurine with the appropriate branched-chain sugar... 

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