Urea derivatives, formation

Ethotoin Ethotoin, 3-ethyl-5-phenylimidazolidine-2,4-dione (9.1.5), is synthesized in basically the same manner as described above, which in this case involves the reaction of benzaldehyde oxynitrile (9.1.2), with urea or ammonium hydrocarbonate, which forms the intermediate urea derivative (9.1.3) which on acidic conditions (9.1.3) cycUzes to 5-phenylhydantoin (9.1.4). Alkylation of this product using ethyliodide leads to the formation of ethotoin (9.1.5) [3,4]. 

Since dorzolamide possesses two chiral centers, an indirect chiral separation has been developed [18]. The procedure employs the chemical derivatization of the secondary amino group of the inhibitor, formation of diastereomeric urea derivatives (each with three chiral centers in the molecule), and their separation under non-ehiral HPLC conditions. Using... 

Simple uretidinediones, as expected, are attacked at the carbonyl with ultimate formation of urea derivatives (Scheme 37) (71JOC3056). More complex derivatives react similarly, although subsequent reaction on labile substituents also occurs (69M1860, 66LA(692)151, 62CJC935, 53JA5439). 

The insertion of carbon monoxide was also the key step in the formation of urea derivatives through the oxidative carbonylation of amines. 6-Amino-... 

The last example focuses not on the functionalization of heterocycles by a transition metal mediated carbon-heteroatom bond forming reaction, but the palladium catalyzed conversion of primary amines, including amino-heterocycles, into urea derivatives. A representative example, shown in 8.38., includes the reaction of an amino-carbazole derivative with morpholine, carbon monoxide and oxygen in the presence of catalytic amounts of palladium(II) iodide. The formation of the urea moiety proceeds with great selectivity and in high yield.49 The reaction works equally well for primary aliphatic and aromatic amines. 

Electrooxidation of the pyrrole unit results in the formation of a pyrrole polymer that coats the electrode surface as it is formed. The amount of polymer deposited can be controlled by the number of CV cycles into the pyrrole oxidation wave. With 30, thick polymer layers give broad CV waves in the quinone voltage region, but thinner layers produce a well-resolved wave for the quinone 0/—1 reduction, which is reasonably stable when the electrodes are placed into fresh electrolyte solution with no 30. As in solution, addition of different urea derivatives causes this wave to shift positive. The relative magnitude of the shifts mirror that seen in solution. Furthermore, the 2 moves back to the original potential when the derivatized electrode is put back into a blank solution containing no urea. 

Initially, water can cause the hydrolysis of the anhydride or the isocyanate, Scheme 28 (reaction 1 and 2), although the isocyanate hydrolysis has been reported to occur much more rapidly [99]. The hydrolyzed isocyanate (car-bamic acid) may then react further with another isocyanate to yield a urea derivative, see Scheme 28 (reaction 3). Either hydrolysis product, carbamic acid or diacid, can then react with isocyanate to form a mixed carbamic carboxylic anhydride, see Scheme 28 (reactions 4 and 5, respectively). The mixed anhydride is believed to represent the major reaction intermediate in addition to the seven-mem bered cyclic intermediate, which upon heating lose C02 to form the desired imide. The formation of the urea derivative, Scheme 28 (reaction 3), does not constitute a molecular weight limiting side-reaction, since it too has been reported to react with anhydride to form imide [100], These reactions, as a whole, would explain the reported reactivity of isocyanates with diesters of tetracarboxylic acids and with mixtures of anhydride as well as tetracarboxylic acid and tetracarboxylic acid diesters [101, 102]. In these cases, tertiary amines are also utilized to catalyze the reaction. Based on these reports, the overall reaction schematic of diisocyanates with tetracarboxylic acid derivatives can thus be illustrated in an idealized fashion as shown in Scheme 29. 

The driving force of the terminal step is the formation of the very stable urea derivative 50, which is formed stoichiometrically. Further reagents employed in peptide bond forming reactions are diimide EDC 52 and triazole HOBT 53 which react similarly to DCC 45 but... 

A dimeric capsule can also be formed by two different tetra-urea molecules, and in aprotic solvents a mixture of two tetra-urea derivatives usually contains not only the two homodimers but also the heterodimer in a more or less statistical ratio. This formation of heterodimers is an additional proof of the dimerization [39], which is also valid when other indications (e.g. m-coupled doublets for aryl protons) fail. As an example, sections of the spectra of tetra-tolylurea (1), tetra-hexylurea (3), and of a mixture of the two are shown in Figure 5.3a-c [37a],... 

However, the statistical formation of heterodimers is not the rule. Examples are known where no heterodimers are formed, e.g. between 1 and tetra-ureas derived from a rigid bis-crown-3 [40] (see Section 7). Further examples will be shown in the next sections. In such cases, the solution of the two tetra-urea calix[4]arenes contains exclusively the two homodimers. 

Give a mechanism for the formation of compound 13. Suggest a reason for the necessity of transforming amine 11 into the urea derivative 12. 

The heterocyclic urea derivative 606 (R = OCOCHaPh or H) with an o-substituted carboxyl group, on treatment with DCC, also cychzes with formation of 607... 

Generation of 10 from the corresponding bis(iminophosphorane) using B0C2O in the presence of DMAP, resulted in the formation of the corresponding cyclic urea derivative. However, low yields of 10 are also obtained from bis(iminophhosphoranes) and isothiocyanates. 

Many commercial herbicides kill weeds by interfering with the action of photosystem II or photosystem I. Inhibitors of photosystem II block electron flow, whereas inhibitors of photosystem I divert electrons from the terminal part of this photosystem. Photosystem II inhibitors include urea derivatives such as diuron and triazine derivatives such as atrazine. These chemicals bind to the Qg site of the D1 subunit of photosystem II and block the formation of plastoquinol (QH2). 

In amino acid and peptide chemistry, the di-ferf-butyl dicarbonate (BocaO) is an extensively used reagent for the clean and rapid Boc-protection of amine functionalities.It is also an efficient ferf-butoxycarbonylating agent for alcohols, thiols, and carbon nucleophiles, and it has been used for the conversion of amines into isocyanates, carbamates, and urea derivatives.The reaction of amino acids with chloroformates to produce N-urethane-protected amino acids if not performed under optimal conditions is accompanied by the formation of N-protected oligomers this has been well documented in the case of and... 

---