Poly Thioesters

S. (2005) Preparation of aliphatic poly(thioester) by the lipase-catalyzed direct polycondensation of... 

Figure 11. Synthesis of LC poly ( aminoester)s and poly( thioester)s by the polycondensation reaction between a mesogenic diacrylic monomer and bissecondary amines and bisthiols, respectively.

POLY(THIOESTERS) Poly(thio-3-methyl-6-oxohexamethylene) 293 DTA heating rate 497... 

Ester-thioester copolymers were enzymatically synthesized (Scheme 7). ° The lipase CA-catalyzed copolymerization of e-caprolactone with 11-mercaptoundecanoic acid or 3-mercaptopropionic acid under reduced pressure produced the polymer with molecular weight higher than 2 x 10". The thioester unit of the resulting polymer was lower than the feed ratio. The transesterification between poly(8-caprolactone) and 11-mercaptoundecanoic acid or 3-mercaptopropionic acid also took place by lipase CA catalyst. Recently, aliphatic polythioesters were synthesized by lipase CA-catalyzed polycondensation of diesters with 1,6-hexanedithiol. ... 

RS+ electrophiles that are electrogenerated in a CH2CI2/BU4NCIO4 solution readily attack even less reactive triple bonds of terminal alkynes [123] and result, after further oxidation and hydrolysis, in a-oxo-thioesters (Scheme 33). Under acidic conditions, it is possible to direct the reaction to the formation of an oligomer, cyclohexa-1,4-phenylene sulfide, or a conductive poly(p-phenylene)sulfide [131,132]. 

CALB-catalyzed copolymerization of CL with 11-mercaptoundecanoic acid (1IMU) leads to the formation of poly(ester-c6>-thioester)s having a Mn of 13.7 kDa (PDI 1.6) after precipitation [30] (Fig. 11). The amount of incorporated IIMU (8.7mol%) was slightly less than the feed ratio (10mol%). Similar results were obtained when using 3-mercaptopropionic acid (3MP) as a comonomer (Mn 14.3 kDa, PDI 1.4). CALB-catalyzed transesterification of pCL with either 1 IMU or 3MP resulted in similar H-NMR and C-NMR spectra as the direct copolymerization of the two monomers, showing that continuous transesterification plays an important role in the microstructure of the polymer [30]. 

CO2-PEG system is also effective for the scandium-catalyzed aldol reactions, and poly(ethylene glycol) dimethyl ether (PEG(OMe)2, MW = 500) is more effective than PEG (Scheme 3.12) [57]. Emulsions in C02-PEG(0Me)2 medium are observed when the concentration of the additive is 1 g/L. Not only benzal-dehyde but also substituted aromatics, aliphatic, and a, /]-unsaturated aldehydes react smoothly, and various silicon enolates derived from a ketones, esters, and thioesters also react well to afford the corresponding aldol adducts in high yields. 

Poly(d -aryl thioesters) 394, treated with thiiranes in the presence of tetrabutylammonium chloride in DMA at 70 °C for 6 h, gave a new modified polymer 395 (Scheme 113) <1996MM6676>. Other examples of polymerization of thiiranes with poly(3 -aryl thioesters) were reported <1996MI68, 1997MI550, 1999MM1407>. 

Polyketide and fatty acid biosyntheses begin with condensation of the coenzyme A thioester of a short-chain carboxylic acid starter unit such as acetate or propionate with the coenzyme A thioester of a dicarboxylic acid extender unit such as malonate or methyl malonate. The driving force for the condensation is provided by the decarboxylation of the extender unit. In the case of fetty acid synthesis, the resulting -carbonyl is completely reduced to a methylene however, during the synthesis of complex poly-ketides, the -carbonyl may be left untouched or variably reduced to alcohol, olefinic, or methylene functionalities depending on the position that the extender unit will occupy in the final product. This cycle is repeated, and the number of elongation cycles is a characteristic of the enzyme catalyst. In polyketide biosynthesis, the full-length polyketide chain cyclizes in a specific manner, and is tailored by the action of additional enzymes in the pathway. 

Similarly, sequence analyses of iterative PKSs can allow the nature of the expected metabolite(s) to be inferred, even though accurate structural predictions are not yet possible. Many catalyze polymerization of malonyl-CoA to make poly-/ -ketomethylene thioester intermediates that undergo a series of aldol cyclization and dehydration reactions to yield aromatic products. Others catalyze the assembly of more reduced polyketide... 

Table 11. Representation of some typical structures of poly(y3-aminoester)s and poly()3-thioester)s.

For thermotropic MCPs, stable Schlieren texture with high strength defects ( 5 =3/2 and 5 = 2) was first reported by Galli et al. [70] for the poly(/3-thioester) ... 

Ghalanbor, Z. Korber, M. Bodmeier, R. Protein release from poly(lactide-co-glycolide) implants prepared by hot-melt extrusion Thioester formation as a reason for incomplete release. Int. J. Pharm. 2012, 438 (1-2), 302-306. 

---