Amines reversible blocking with

SCHEME 4.2 Scale of reactivity of various amines toward a model pentacyclocarbon-ate. (Reprinted from E. Delebecq, J-P. Pascault, B. Boutevin, and F. Ganachaud, On the Versatility of Urethane/Urea Bonds Reversibility, Blocked Isocyanate, and Non-Isocyanate Polyurethane, Chem. Rev. 113 (2013) 80-118. With permission.)... 

Ketones can reversibly react with primary amines with the loss of water to give ketimines (Figure 2.51). They can be considered blocked... 

Citraconic anhydride (or 2-methylmaleic anhydride) is a derivative of maleic anhydride that is even more reversible after acylation than maleylated compounds. At alkaline pH values (pH 7-8) the reagent effectively reacts with amine groups to form amide linkages and a terminal carboxylate. However, at acid pH (3-4), these bonds rapidly hydrolyze to release citraconic acid and free the amine (Figure 1.86) (Dixon and Perham, 1968 Habeeb and Atassi, 1970 Klapper and Klotz, 1972 Shetty and Kinsella, 1980). Thus, citraconic anhydride has been used to temporarily block amine groups while other parts of a molecule are undergoing derivatization. Once the modification is complete, the amines then can be unblocked to create the original structure. 

The Step 1 product (0.25 mmol) was added to the wells of a reaction block containing 5 ml THF and treated with yV-benzyl-/V-ethylamine (0.5 mmol) or other selected amines neat. The reaction block was shaken 24 hours, filtered, and concentrated. The residue was purified by reverse-phase HPLC with water/acetonitrile (0.1% TFA) and the product isolated as the trifluoroacetate salt. 

Borylated ferrocenes have been exploited by Wagner as building blocks for the assembly of macrocycles and coordination polymers (Scheme 15). Treatment of the diborylated ferrocene l,L-fc(BMe2)2 with the bifunctional aromatic amines pyrazine and 4,4 -bipyridine, respectively, led to spontaneous and reversible formation of (89) and related ferrocenylborane polymers.The polymeric nature of... 

Analysis of the enantiomeric ratios of several p-blocking drugs (l-aryloxy-3-isopropylamino-2-propanol derivatives) is carried out by HPLC with UV or fluorescence detection after derivatization with (R)-NEI or (i )-(+)-l-(l-phenyl)ethyl isocyanate (in a reversed-phase system), or (S)-NEI (on silica gel) only the amine function of the drugs reacts with the NEI the hydroxy group does not. Similar schemes for HPLC determination of enantiomeric purity of tetrahydrofolate derivatives and of fluoxetine are also reported. 

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