Hydrazones exchange

Ingerman, L. A. Waters, M. L. Photoswitchable dynamic combinatorial libraries Coupling azobenzene photoisomerization with hydrazone exchange. J. Org. Chem. 2009, 74, 111-117. 

Figure 3.25 Racemic dynamic combinatorial library targeting (-)-adenosine. Left Racemic porline containing dipeptide library building block. Middle Various enantiomeric oligomers formed through reversible hydrazone exchange. Right The SS enantiomer selected upon equilibration with (-)-adenosine.

Carbonic anhydrase [17] Acyl hydrazone exchange <300 ESI-FTICR-MS... 

In this ESI-FTMS screening proof-of-concept experiment, a DCL was generated using the hydrazone exchange reaction from two hydrazide fragments (1 and 2) and five aldehyde fragments (A-E) (Scheme 7.2). 

Scheme 7.2 Dynamic combinatorial chemistry targeting carbonic anhydrase. (a) Fragments for hydrazone exchange, (b) Dynamic combinatorial library generation.

Hydrazide 1 was designed as the CA anchor fragment and hence necessitated dual functionality an Ar-SO NH moiety for reliable CA affinity and a hydrazide moiety to take part in hydrazone exchange. Hydrazide 2 lacked the sulfonamide moiety of 1, but was still able to participate in hydrazone exchange and thus functioned as a control compound. Fragments A-E, the exchange partners for 1 and 2, were selected to introduce an array of tails onto 1 to enable exploration of periphery recognition interactions with CA. 

Compound 203 (R1 = R2 = H, X = Br) underwent hydrazone exchange with hydrazine hydrate to give 2-amino-5-bromobenzophenone hydra-zone. The same benzotriazocine was ring-opened with lithium aluminum hydride to afford 2-benzyl-4-bromoaniline, while hydrolysis of the compound yielded 2-amino-5-bromobenzophenone (83CHE337). 

Figure 7.12 Fragments equipped with a hydrazide (1 and 2) or aldehyde (A-E) functional groups for DCC utilizing hydrazone exchange and targeting carbonic anhydrase.

Scheme 7.3 Dynamic combinatorial library utilizing hydrazone exchange and targeting...

Rodriguez-Docampo Z, Otto S (2008) Orthogonal or simultaneous use of disulfide and hydrazone exchange in dynamic covalent chemistry in aqueous solution. Chem Commun 2008 5301-5303... 

Figure 1.3 Continued) (n) imine exchange, boroxine formation, (v) transboroxoaromatic (o) hydrazone exchange, (p) oxime exchange, esterification, (w) reversibie resorcinoi and (q) nitrone exchange, (r) aikene metathesis, 1,4-butanediai condensation, (x) metai-...

AChE acyl hydrazone exchange 66 bis-pyridinium structure [24]... 

HPr kinase/phosphatase acyl hydrazone exchange 440 2-aminobenzimidazole m... 

Acyl hydrazone exchange has also been probed as reversible chemistry for the generation of oligotopic and directional carbohydrate DCLs of larger size [45]. 

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