Biosynthesis structural considerations

Another structural consideration relevant to biosynthesis is the fact that, within a chain, each D-glucosyl residue is rotated approximately 180° with respect to its neighbor, as depicted in 1. Thus, cellobiose may actually be considered to be the true repeating-unit within the chain, and it is necessary to consider whether some activated form of the disaccharide (rather than of D-glucose) might be the donor for chain elongation this point will be considered again in Section V,2. 

Battersby et al. used (13S)- and (13R )-labeled scoulerine (58b) to study the biosynthesis of rhoeadine. Both of them were incorporated by living P. rhoeas plants into rhoeadine. This alkaloid, isolated from plants fed with (7J 5)-labeled scoulerine, had lost 79% of the tritium present in the precursor, whereas the (/37 )-labeled scoulerine afforded rhoeadine which retained 74% of the original tritium. Bearing in mind the configurational purity of the precursors, these values prove that a stereospecific loss of the pro-5-hydrogen occurs from C-13 of scoulerine at some stage of its transformation into rhoeadine. It seems likely from structural considerations... 

Kojic acid, 5-hydroxy-2-(hydroxymethyl)-4//-pyran-4-one1 (II), is produced from carbohydrate sources in an aerobic process by a variety of microorganisms. The acid was discovered in 1907, its structure was established in 1924, and its chemical synthesis from D-glucose was achieved in 1930. Since then, a considerable amount of study has been devoted to the biosynthesis of kojic acid, and numerous publications have dealt with its chemical and biological properties. After nearly half a century, kojic acid remains a scientists curiosity, without industrial importance. It con-... 

Since the chemistry of nucleic acids was last discussed in this Series,1 publications on the subject have appeared at an unprecedented rate. Degradation products have been further investigated and their structures are more firmly established. Moreover, studies of the properties of these materials have led to a fuller understanding of the behavior of polynucleotides. Emphasis will be laid on the organic chemistry of nucleic acids, and many physicochemical investigations will not be discussed. The period under review has seen the beginning of an understanding of the biosynthesis of nucleic acids, but space does not allow of a consideration of this aspect of the subject. 

Saponins are glycosylated secondary metabolites that are widely distributed in the Plant Kingdom.3,4 They are a diverse and chemically complex family of compounds that can be divided into three major groups depending on the structure of the aglycone, which may be a steroid, a steroidal alkaloid, or a triterpenoid. These molecules have been proposed to contribute to plant defense.3 6 Saponins are also exploited as drugs and medicines and for a variety of other purposes.4 Despite the considerable commercial interest in this important group of natural products, little is known about their biosynthesis. This is due in part to the complexity of the molecules, and also to the lack of pathway intermediates for biochemical studies. 

Vitamins. The vitamins are natural organic compounds of considerable diversity that occur widely. The name derives from the Latin vita (life) and amin, a shortened form of amine. The name reflects the historical discovery of these substances, not all of which are amines. They are all of relatively low molecular weight, especially compared to peptides but in a range comparable to steroids. These substances are uniformly active and play various roles in biosynthesis and metabolism. The vitamins are too numerous to detail here but the most common examples are illustrated. They are classed using the common system, that is, water or fat soluble, depending on their approximate level of hydrophobicity or hydrophilicity. Their names are typically nonsystematic but the diversity of their structures requires that the trivial names be used. 

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