Thioacetate groups

The much simpler steroid, 253, was fortuitously found to fulfill this role when injected into animals. Its lack of oral activity was overcome by incorporation of the 7a-thioacetate group. Reaction of the ethisterone intermediate, 77b, with a large excess of an organomagnesium halide leads to the corresponding acetylide salt carbonation with CO2 affords the carboxyllic acid, 251. This is then hydrogenated and the hydroxy acid cy-clized to the spirolactone. Oppenauer oxidation followed by treatment with chloranil affords the 4,6-dehydro-3-ketone (254). Conjugate addition of thiolacetic acid completes the synthesis of spironolactone (255), an orally active aldosterone antagonist. ... 

The aldehyde function at C-85 in 25 is unmasked by oxidative hydrolysis of the thioacetal group (I2, NaHCOs) (98 % yield), and the resulting aldehyde 26 is coupled to Z-iodoolefin 10 by a NiCh/CrCH-mediated process to afford a ca. 3 2 mixture of diaste-reoisomeric allylic alcohols 27, epimeric at C-85 (90 % yield). The low stereoselectivity of this coupling reaction is, of course, inconsequential, since the next operation involves oxidation [pyridinium dichromate (PDC)] to the corresponding enone and. olefination with methylene triphenylphosphorane to furnish the desired diene system (70-75% overall yield from dithioacetal 9). Deprotection of the C-77 primary hydroxyl group by mild acid hydrolysis (PPTS, MeOH-ClHhCh), followed by Swem oxidation, then leads to the C77-C115 aldehyde 28 in excellent overall yield. 

The dimeric Rh11 complex [Rh2(MeCOS)4(MeCOSH)2] contains four bridging thioacetate groups the two thioacetic acid ligands are in the thione form and are each bound via the sulfur atom to one of the rhodium atoms.133 The Ru" complex [Ru(MeCOS)2(CO)(Ph3 P)2] is known in two isomeric forms.134... 

The dithiane anion is a good nucleophile in SN2 reactions. After it has been alkylated, the thioacetal group can be removed by hydrolysis using Hg2+ as a Lewis acid catalyst. 

The hydroxyl group of (+)-32 was protected as a methoxymethyl ether to give ether (+)-63 in 80% yield (Scheme 12). To reduce the carbonyl group of (+)-63 to a methylene moiety of (+)-66 (Scheme 13), we tried the thioacetal reduction method. However, the attempt was unsuccessful because of the exchange of the acetal group at the 1-position by a thioacetal group. Although we also tried the... 

In order to confirm the structures of solanapyrones, chemical synthesis of these phytotoxins were attempted based on biogenetic consideration [55], The retro synthesis envisaged intramolecular Diels-Alder reaction of the achiral polyketide triene (a), a key intermediate, which is further divided into a pyrone moiety (b) and a diene moiety (c). The moieties a and b were prepared from dehydroacetic acid and hexadienyl acetate, respectively. Aldol condensation of the aldehyde (72) with the dithioacetal (73) gave a dienol, which was further converted to a triene (74). The intramolecular Diels-Alder reaction of 74 in toluene at 170-190 °C for 1 hr in a sealed tube yielded a mixture of the adducts (75) and (76) in a ratio of 1 2. This product ratio depends on the solvents, i.e. in water (1 7), and should be useful in differentiating between artificial and enzymatic reactions in biosynthetic studies. Removal of the thioacetal groups in 75 and 76 yielded solanapyrone A (67) and D (70) in a ratio of 3 5. Though solanapyrone D (70) had not been isolated from the natural resources at this stage, the structure and stereochemistry were confirmed by H NMR spectrum. 

Transtkioacetattzation. This carbonyl compound and mesoxalic acid (keto-malonic acid) are suitable for transfer of thioacetal groups from various aldehydes and ketones. Acetic acid is a satisfactory medium a strong mineral acid is also used. Yields, 50-907 "... 

Cleavage of tUoaceta groups. Sulfuryl chloride in the presence of wet silica gel oxidatively cleaves thioacetal groups at room temperature. Monosulfoxides arc presumably intermediates. ... 

Kisserwan, H. Enhancement of photovoltaic petfomiance of a novel dye, T18 , with ketene thioacetal groups as electron donors for high efficiency dye-sensitized solar cells. Inorg. Chimi. Acta, 2010, 363,2409-2415. 

Application of a formaldehyde thioacetal group for protection and introduction of cystine has been demonstrated in a new synthesis of oxidized glutathione. A summary of this interesting approach has been entered in Chart 5 and additional details will be included in the pentapeptide table of a subsequent volume. Another pentapeptide synthesis published in the fall of 1972 corresponded to positions 1-5 of the fibrinogen protein C-chain. The latter substance is of interest from the standpoint of the clotting process which is complex and involves in part release of two of the three protein chains of fibrinogen by the enzyme thrombin. The fibrinogen pentapeptide synthesis was also used to further e.xplore the 4-picolyl ester (OPic) method of peptide bond formation. 

Christopher N. Bowman and Kathryn A. Berchtold, (Meth)acrylic and (Meth)acry-lamide Monomers Comprising Cyclic Acetal/Thioacetal Groups, Polymerizable Compositions, and Polymers Obtained. Department of Chemical Engineering, University of Colorado, Boulder, Colorado, USA. 

Preparative Methods the synthesis of 1 was achieved by protection of the amino alcohol 2 with B0C2O to give the carbamate 3. Conversion to the mesylate 4 was followed by reaction with cesium thioacetate to give the thiol acetate 5. Finally, a selective reduction of the thioacetate group afforded 1 (eq 1). ... 

Similar prolonged ethanethiolysis of D-mannopyranosylstreptomycin 46) produced ethyl 1-thio-a- and -jS-D-mannopyranosides, isolated as acetates. Likewise, streptomycin was cleaved with ethanethiol and hydrochloric acid 47) to produce ethyl 1-thiostreptobiosaminide diethyl dithioacetal hydrochloride. This type of cleavage is useful in structure determination since the carbonyls are protected with thioacetal groups as they are released 4S). It was by means of this reaction that the nature of the acid-sensitive strep-tose portion of streptomycin was elucidated. (See Chapter X.)... 

Anomalies have also been shown in the oxidation behavior of lead tetraacetate 225). Oxidant is consumed in the case of derivatives of D-arabinose thioacetal this consumption is affected by the position of the glycol groups in the various compounds relevant to the thioacetal group. 

---