Carbamates Type

Carbamate linker systems (Fig. 9, [19,182-191]) are often produced by the transformation of an alcohol to a carbonate functionality. Afterwards, the carbonate can be reacted with amines and amide coupUng reagents to give carbamates. This strategy is for example used by Und n et al. [192] by the addition of 4-nitrophenylchloroformate (4-NPCF) to a 4-methyl-benzhydrylamine polystyrene (MBHA-PS)-based resin and further addition of an alkylamine. A similar sequence is conducted with a solid-supported hydroxy-functionality that is converted via phosgene addition into the chlo-roformate. Addition of amines then gives resin-bound carbamates [193]. 

Another possibility to synthesize carbamates on a solid support is the addition of activating reagents that transform alcohols directly into (activated) carbamates Hke NAi-disuccinimidyl carbonate (DSC) or carbonyl diimidazole (CDI). These activated carbamates then are easily reacted to the target linker via addition of amines [193,194]. 

Good results are also achieved by a recently developed approach that is successful through the coupHng of isocyanates on hydroxyl-containing resins [195]. 

The group of Hiemstra developed a reduction-cleavage protocol for carbamates on solid supports [184]. In order to get methyl amines, the activated 

More common than reductive methods on carbamate resins are substitution protocols which result in formation of urea-type compounds 207 that can be acyclic or even cyclic if the attacking amine is part of the solid-supported carbamate. 

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The PO mode is a specific elution condition in HPLC enantiomer separation, which has received remarkable popularity especially for macrocyclic antibiotics CSPs and cyclodextrin-based CSPs. It is also applicable and often preferred over RP and NP modes for the separation of chiral acids on the cinchonan carbamate-type CSPs. The beneficial characteristics of the PO mode may arise from (i) the offset of nonspecific hydrophobic interactions, (ii) the faster elution speed, (iii) sometimes enhanced enan-tioselectivities, (iv) favorable peak shapes due to improved diffusive mass transfer in the intraparticulate pores, and last but not least, (v) less stress to the column, which may extend the column lifetime. Hence, it is rational to start separation attempts with such elution conditions. Typical eluents are composed of methanol, acetonitrile (ACN), or methanol-acetonitrile mixtures and to account for the ion-exchange retention mechanism the addition of a competitor acid that acts also as counterion (e.g., 0.5-2% glacial acetic acid or 0.1% formic acid) is required. A good choice for initial tests turned out to be a mobile phase being composed of methanol-glacial acetic acid-ammonium acetate (98 2 0.5 v/v/w). 

Although the cinchonan carbamate-based CSPs are of primary interest for the separation of chiral acids, it needs to be stressed that the scope of application is, however, not restricted to chiral acids. A few reports in the literature deal with the separation of the enantiomers of neutral and weakly basic chiral compounds, respectively, on quinine carbamate-type CSPs [50-54]. Both RP and NP modes may be applicable. 

Replacement of the carbamate group with isosteric functionalities such as an IV-methyl carbamate, urea, or amide group clearly confirmed the favorable qualities of the carbamate group [57], While the introduction of a urea group, as in case of iV-9-(tert-butylcarbamoyl)-9-desoxy-9-aminoquinine selector, instead of carbamate functionality turned out to be virtually equivalent in terms of enantiorecognition capabilities [57,58], the enantiomer separation potential was severely lost on iV-methylation of the carbamate group, like in 0-9-(N-me hy -N-tert-butylcarbamoyl)quinine [32,58], or its replacement by an amide, such as in case of Af-9-(pivaloyl)-9-desoxy-9-aminoquinine selector [57,58], For example, enantioselectivities dropped for DNB-alanine from 8.1 for the carbamate-type CSP, over 6.6 for thein-ea-type CSP, to 1.7 for the amide-type CSP, and 1.3 for the A -methyl... 

The calorimetric binding isotherms of the carbamoylated quinine and quinidine selectors clearly reveal that the heats released upon binding are strongly different for 5- and R-enantiomers of DNB-Leu, which is commensurate with the remarkable enantioselective molecular recognition capability of these selectors (Figure 1.14a,b). As can be seen from Table 1.4, the binding constants for R- and 5-enantiomers differ by about one order of magnitude in case of the carbamate-type selectors. Furthermore,... 

Modification of Neamine Use of Carbamate Type of Protecting Groups 145... 

There are a few reports on the amination of a-metallated carbonyl compounds with 0-(arenesulfonyl)hydroxylamine-type reagents. However, in recent years there has been substantial progress in Af-(alkoxycarbonyl) 0-(arenesulfonyl)hydroxylamine [alkyl N-(arenesulfonyloxy)carbamate]-type reagents for the amination of enolates and eniminates. 

Second-Order Rate Constants kB at 25°C for the Hydrolysis of Some Substituted Phenyl N-Methyl-N-Phenyl Carbamates (Type II)a... 

Urthophenylenediamine (OPDA) is an important intermediate of several biologically active compounds, including the benzimidazene--carbamate type fungicides [1]. There are different routes for the synthesis of OPUA. In the present work an attempt was done to prepare OPOA from 4-chloro-2-nitroaniline (CNA). CNA can be obtained by nitration and subsequent ammonolysis of para-dichloro-benzcne [ 1]. 

I Stober, HR Schulten. Combined application of high-pressure liquid chromatography and field desorption mass spectrometry for the determination of biocides of the phenylurea and carbamate type in surface water. Sci Total Environ 16 249-262, 1980. 

Carbamate type Crops C8 HPLC with post-column basic hydrolysis and electrochemical detection [65]... 

Carbamate type Thiocarbamate type Apples Solid-phase extraction HPLC, UV detection and GC flame detection [81]... 

Seven carbamate types Fruit and Extraction then gel permeation HPLC with pre-column [85]... 

Carbamate type and its Fruit and Solvent extraction, clean-up on HPLC with post-column [87]... 

Substituted urea and carbamate type Plants Acetone extraction TLC and GC 0.001-0.5 ppm [147]... 

Pesticides can be analyzed on a C18 column, the chlorinated hydrocarbon type (chlordane) at 80% An/water UV, 220 nm, the carbamate type (sevin) at 40% An/water UV, 254 nm, and the organic phospahate (malathion) at 50% An/water with UV, 192 nm or with a CAD. The organic phosphate types are hard to detect at low concentration and various phosphate analysis techniques have been evaluated. LC/MS, where available, is the technique of choice for analyzing all of these pesticides, but especially the organic phosphates, in a general gradient HPLC scheme. 

In Section 17.3, rodenticidal thioureas, insecticidal thiocyanates, and fungicidal dithiocarbam-ates were discussed. Sulfur is a common constituent of other classes of insecticides. These prominently include the organophosphate insecticides discussed in Chapter 18. Mobam (Figure 17.10) is a contact insecticide of the carbamate type, closely related in structure and function to the well-known carbamate insecticide carbaryl (see Figure 15.8). Mobam has been found to have a relatively high toxicity to laboratory mammals and is considerably more toxic than carbaryl. 

Carbamate type Hexane 1% GE- Electron Conversion to 0.005ppm [429]... 

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