Proclavaminate

Scheme 10.30 Part of clavulanic acid biosynthesis. Bonds installed byclavaminic acid synthase (CAS) are circled. CAS clavaminic acid synthase. PAH proclavaminic acid amidino hydrolase.

The cis P-lactams 57 are shown to act as cholesterol absorption inhibitors <96BMCL1947> and 58, an analogue of the dipeptide Phe-Gly methyl ester, is a protease inhibitor <96BMCL983>. A straightforward synthesis of proclavaminic acid 59, a biosynthetic precursor of clavulanic acid, is reported <96TA2277>. 

Proclavaminate amidino hydrolase (PAH) is one of a number of enzymes that are Mn activated and whose amino acid sequence shows strong homology with arginase. PAH catalyzes the hydrolysis of a guanidino group to give proclavaminate and urea (Equation (8)) ... 

Differently C-labeled ornithine is incorporated both into 54 and clavam-2-carboxylic acid with similar efficiency and the same regiochemistry [116]. Also C-labeled clavaminic and proclavaminic acids are incorporated into the same compounds with equal efficiency. The theory of a common biosynthetic pathway up to clavaminic acid for 54 and clavams came from the decarboxylation of clavaldehyde formed by oxidative deamination of clavaminic acid and therefore proposed to be the point of the decarboxylation branch point leading to clavam-2-carboxylic acid (Figure 4.25) [117]. 

Clavaminate synthase is one of the enzymes involved in the biosynthesis of the p-lactamase inhibitor clavulanic acid. The key function of the enzyme is conversion of the monocyclic p-lactam, proclavaminic acid, to the bicyclic clavaminic acid. This process requires ferrous ion as co-factor and a-ketoglutarate (a-KG) and molecular oxygen as cosubstrate. The enzyme has been purified from Streptomyces clavuligerus, Mj- 47 kDa [340] and Streptomyces antibioticus [341]. Binding of histidine and cysteine to iron is suggested [342]. In this case one atom of dioxygen is incorporated into succinate rather than to form hydroxylation products. The mechanism has been studied recently [343-345], and Scheme 20, which involve Fe =0 as an active species, has been proposed... 

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