5. ANTIBIOSIS AND ANTIBIOTICS
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Mycosamine (XXVII) is a moiety of the heptaene macrolides amphotericin Β and candidin, and of the tetraene macrolides pimaricin and
nystatin. In fact, this amino sugar is thought to be present in most tetraene antibiotics. However, in PA-166, it is replaced by an unidentified
amino sugar which is not of the deoxy type. Lankavose (XXVIII) and
4-O-acetylarcanose (XXIX) have been recently identified in lankamycin
(62k). Lankavose is probably identical with chalcose, a degradation
product from the antibiotic chalcomycin (63).
Finally, sugars are found in some of the polypeptide antibiotics of the
streptothricin group produced by streptomycetes: glucosamine in roseomycin, α-D-gulosamine (XXXa) in the streptolins A and Β and in streptothricin, an unidentified aminohexose in geomycin, and roseothricin A,
a reducing sugar in racemomycin B.
3. Occurrence and Biosynthesis of Sugars and Derivatives
Sugars and sugar derivatives, common and unusual, are also found
in other microbial products (64) besides antibiotics, notably in bacterial
slimes, capsules, cell walls (65a) and substances (for instance antigens)
more or less firmly bound to the latter structure. Among the common
ones, glucose itself is rather rare while others are frequently found:
D-ribose (very likely synthesized by way of the pentose phosphate cycle),
D-deoxyribose (sometimes arising from direct reduction of the former),
galactose, mannose, fucose, galacturonic acid, gluconic acid (all arising
from D-glucose), D-glucosamine (formed either by glutamine amination
of fructose 6-phosphate or by way of glucosone).
Most of the unusual sugars and derivatives seem to arise from a more
"normal" parent, such as glucose, ribose, or glucosamine, through oxidation, reduction, decarboxylation, epimerization, etc., all these reactions
occurring while the sugar is combined to a nucleotide. N-Methylation
(frequently through methionine) and iV-acetylation (generally involving
acetyl coenzyme A) also occur frequently. Several of the sugar derivatives reviewed—for instance, 2-deoxystreptamine, streptidine, neoinosamine—are structurally related to the cyclic inositols. So is actinamine
(XXXb), a degradation product (65b,c)
of the antibacterial agent
actinospectacin, from Streptomyces spectabilis (65d,e), for which the
complete structure (XXXc) was recently proposed (65f). Mi/o-inositol
has been shown to be a precursor of streptidine in streptomycin (66a).
However, the biosynthesis of the inositols is as yet poorly understood. It
is often said that they are probably formed by a direct cyclization of
hexose. In fact, the conversion of glucose into inositol by parsley leaves
has been recently demonstrated (66b).
271
Mycosamine (XXVII) is a moiety of the heptaene macrolides amphotericin Β and candidin, and of the tetraene macrolides pimaricin and
nystatin. In fact, this amino sugar is thought to be present in most tetraene antibiotics. However, in PA-166, it is replaced by an unidentified
amino sugar which is not of the deoxy type. Lankavose (XXVIII) and
4-O-acetylarcanose (XXIX) have been recently identified in lankamycin
(62k). Lankavose is probably identical with chalcose, a degradation
product from the antibiotic chalcomycin (63).
Finally, sugars are found in some of the polypeptide antibiotics of the
streptothricin group produced by streptomycetes: glucosamine in roseomycin, α-D-gulosamine (XXXa) in the streptolins A and Β and in streptothricin, an unidentified aminohexose in geomycin, and roseothricin A,
a reducing sugar in racemomycin B.
3. Occurrence and Biosynthesis of Sugars and Derivatives
Sugars and sugar derivatives, common and unusual, are also found
in other microbial products (64) besides antibiotics, notably in bacterial
slimes, capsules, cell walls (65a) and substances (for instance antigens)
more or less firmly bound to the latter structure. Among the common
ones, glucose itself is rather rare while others are frequently found:
D-ribose (very likely synthesized by way of the pentose phosphate cycle),
D-deoxyribose (sometimes arising from direct reduction of the former),
galactose, mannose, fucose, galacturonic acid, gluconic acid (all arising
from D-glucose), D-glucosamine (formed either by glutamine amination
of fructose 6-phosphate or by way of glucosone).
Most of the unusual sugars and derivatives seem to arise from a more
"normal" parent, such as glucose, ribose, or glucosamine, through oxidation, reduction, decarboxylation, epimerization, etc., all these reactions
occurring while the sugar is combined to a nucleotide. N-Methylation
(frequently through methionine) and iV-acetylation (generally involving
acetyl coenzyme A) also occur frequently. Several of the sugar derivatives reviewed—for instance, 2-deoxystreptamine, streptidine, neoinosamine—are structurally related to the cyclic inositols. So is actinamine
(XXXb), a degradation product (65b,c)
of the antibacterial agent
actinospectacin, from Streptomyces spectabilis (65d,e), for which the
complete structure (XXXc) was recently proposed (65f). Mi/o-inositol
has been shown to be a precursor of streptidine in streptomycin (66a).
However, the biosynthesis of the inositols is as yet poorly understood. It
is often said that they are probably formed by a direct cyclization of
hexose. In fact, the conversion of glucose into inositol by parsley leaves
has been recently demonstrated (66b).