Thiones conjugated

Sulphobromophthalein-gluta-thione conjugate Tamm-Horsfall glycoprotein... 

Reduction of the pyridyl disulfide end after SPDP modification releases the pyridine-2-thione leaving group and generates a terminal—SH group. This procedure allows sulfhydryl-reactive derivatives such as maleimide-activated enzymes (Chapter 26, Section 2.3) to be conjugated with DNA probes for use in hybridization assays (Malcolm and Nicolas, 1984). 

In solution aliphatic and aromatic sulfines combine with aromatic and aliphatic thiones to yield 1,2,4-oxadithiolanes.169,170 Cycloadducts with only aromatic substituents could not be obtained, since the conjugation energy of aromatic sulfine drives the equilibrium to the reactant side.170 Thiobenzophe-none- and thiofluorenone-sulfines react with 3 to afford 1,2,4-trithiolanes.171 This is interpreted by assuming that 1,2,4-oxadithiolanes are formed in a first step, hence converted to 1,2,4-trithiolane. 

Similar studies have recently been extended to aminopyridones and thiones and to aminopyrimidones (Barlin jmd Pfleiderer, 1971 Barlin, 1972). Protonation of 3- and 5-amino-2-hydroxypyridine and 3,4-diamino-2-hydroxypyridine occurs first at the 3- (or 5-) amino-group, but 4- and 6-amino-2-hydroxypyridine and 2- and 3-amino-4-hydroxypyridine first protonate at the oxygen atom, because the amino-group is involved in conjugation with the partially positively charged ring nitrogen. Similar results are found for the amino-pyridine-2(and 4)-thiones (Barlin, 1972). 

Ueno and Okawara (184) were the first to explicitly formulate a conjugated thiocarbonyl ylide as an intermediate in the reaction of l,3-dithiolane-2-thione with 4-bromophenacyl bromide. The initially formed thiocarbonyl ylide undergoes deprotonation with sodium hydride to give 2-(4-bromophenyl)-l-oxa-4,6,9-trithias-piro[4.4]non-2-ene. 1,3-Diacylated thiocarbonyl ylides of type 149 (Scheme 5.45) have also been proposed as intermediates in the reaction of 1,3-diphenylpropane-1,3-dione with thionyl chloride. This reaction leads to 2,2,4-tribenzoyl-5-phenyl-... 

Besides being presently the most efficient method for site-directed interchain disulfide bridging of two different cysteine peptides, this procedure is also recommended for a controlled peptide-protein conjugation by reacting Npys-protected cysteine peptides with properly thiol-functionalized protein carriers. 1761 In this conjugation procedure the amount of peptide grafted to the protein is quantitatively determined by measuring spectro-photometrically at 430 nm the amount of 3-nitropyridine-2(l//)-thione liberated in the reaction. An example of this approach is outlined in Scheme 18. 

Different synthetic routes have been used to prepare these carbenes (Scheme 8.6). The most common procedure is the deprotonation of the conjugate acid. In early experiments, sodium or potassium hydride, in the presence of catalytic amounts of either f-BuOK or the DMSO anion were used. ° Then, Herrmann et al. showed that the deprotonation occurs much more quickly in liquid ammonia as solvent (homogeneous phase), and many carbenes of type IV have been prepared following this procedure. In 1993, Kuhn and Kratz" developed a new and versatile approach to the alkyl-substituted N-heterocyclic carbenes IV. This original synthetic strategy relied on the reduction of imidazol-2(3//)-thiones with potassium in boiling tetrahydrofuran (THF). Lastly, Enders et al." reported in 1995 that the 1,2,4-triazol-5-ylidene (Vila) could be obtained in quantitative yield from the corresponding 5-methoxy-l,3,4-triphenyl-4,5-dihydro-l//-l,2,4-triazole by thermal elimination (80 °C) of methanol in vacuo (0.1 mbar). 

Cycloaddition of 2-ethoxy-2,3-dihydro-4//-1,3-benzoxazin-4-one with conjugated diene 167 gave tetrahydropyrido[2,l-b][l,3]oxazin-6-ones (168) (71JHC865). Diels-Alder reactions of 3,4-dihydroisoquinolines and thioketenes (169), formed in situ, yielded 4,6,7,116-tetrahydro[l,3]ox-azino[2,3-a]isoquinoline-4-thiones [83AG(E)55 88CB1165],... 

As may be seen, the dominant feature of much of the chemistry of thiins is the tendency to form maximally conjugated ring systems such as pyrones or thiones, and alkylidene or... 

Apply the filtered reaction mixture to the S-200 column (see Section 2., item 10a) and elute with PBSE at a flow rate of between 10 and 20 mL/h to separate the anti-body--toxin conjugate from the excess of the RIP and the pyndme-2-thione released dunng the reaction Collect fractions of approx 2 mL in vol (see Notes 18 and 19). 

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