Cocatalysis catalysis of synthetic reactions

Processes of this type have been realized in supramolecular phosphorylation reactions. Indeed, the same [24]-N6C 2 macrocycle 38 as that already used in the studies of ATP hydrolysis was also found [5.60] to mediate the synthesis of pyrophosphate from acetylphosphate (AcP). Substrate consumption was accelerated and catalytic with turnover following the steps (1) substrate AcP binding by the proto-nated molecular catalyst 38 (2) phosphorylation of 38 within the supramolecular complex, giving the phosphorylated intermediate PN 81 (3) binding of the substrate HP042 (P) (4) phosphoryl transfer from PN to P with formation of pyrophosphate PP (Fig. 8) (5) release of the product and of the free catalyst for a new cycle [5.60]. PP is also formed in the hydrolysis of ATP in the presence of divalent metal ions [5.61]. 

This process was extended to the phosphorylation of various substrates, in particular to the synthesis of ATP from ADP in mixed solvent [5.62a] and in aqueous solution in the presence of Mg2, probably via formation of a ternary catalytic species 83 [5.62b]. The latter abiotic ATP generating system has been coupled to sets of ATP consuming enzymes resulting in the production of NADH by a combined artificial/natural enzymatic process (Fig. 9) [5.63]. 

Templates possessing two hydrogen bonding subunits bind two substrates forming a ternary complex in which the substrates are positioned so as to facilitate bond formation between them [5.64a]. In a related way, the rate and stereoselectivity of a bimolecular Diels-Alder reaction are substantially increased by binding both the diene and the dienophile within the cavity of a tris-porphyrin macrocycle [5.64b]. 

A macrobicyclic thiazolium cyclophane 84 functions as a model of thiamine pyrophosphate-dependent ligases and effects benzoin condensations [5.38, 5.65a, A.l 1], Acyl transfer is catalysed by formation of a ternary complex between a cyclophane receptor and two substrates [5.65b]. 

Difunctional binding and catalysis has been observed in functionalized cyclo-dextrins [5.66] and in a hydrogen bonding cleft [5.67], Functionalized crown ethers have been used as reagent for peptide synthesis [5.68]. Self-replication processes also involve bond formation reactions they will be discussed in Section 9.6. 

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