Synthesis of, partial

Acetates. Because of the significant interest in selective acetylation reactions of sucrose, the need for a convenient and unambiguous method of identification has been recognized (34,35). The position of an acetyl group in a partially acetylated sucrose derivative can be ascertained by comparison of its H-nmr acetyl methyl proton resonances after per-deuterioacetylation with those of the assigned octaacetate spectmm. The synthesis of partially acetylated sucroses has generally been achieved either by way of selectively protected derivatives such as trityl ethers and cychc acetals or by direct selective acetylation and deacetylation reactions. 

A recently developed application of the Ramberg-Backlund reaction is the synthesis of C-glycosides. The required thioethers can be prepared easily by exchange with a thiol. The application of the Ramberg-Backlund conditions then leads to an exocyclic vinyl ether that can be reduced to the C-nucleoside.95 Entries 3 and 4 in Scheme 10.6 are examples. The vinyl ether group can also be transformed in other ways. In the synthesis of partial structures of the antibiotic altromycin, the vinyl ether product was subjected to diastereoselective hydroboration. 

Trityl ethers and acetals of sucrose have generally been used as precursors for the synthesis of partially acylated derivatives of sucrose. Deacetalation of 3,4,3, 4 -tetra-0-acetyl-2,l 6,6 -di-0-(diphenylsilyl)sucrose (33) and 3,3, 4, 6 -tetra-0-acetyl-2,l 4,6-di-0-isopropylidenesucrose (35) with aqueous acetic acid for 25 min at 50° gave 3,4,3, 4 -tetra-0-acetylsucrose27 (34) and 3,3, 4, 6 -tetra-0-ace-tylsucrose32 (36), respectively. Synthesis of 2,3,4,3, 4 -penta-0-acetyl-... 

K Barlos, D Gatos, S Kutsogianni, G Papaphotiou, C Poulus, T Tsegenidis. Solid phase synthesis of partially protected and free peptides containing disulphide bonds by simultaneous cysteine oxidation-release from 2-chlorotrityl resin. Int J Pept Prot Res 38, 562, 1991. 

Phosphoproteins.—A chemical synthesis of partially and fully phosphorylated protamines has been described during the past year,98 and structural requirements for the enzymatic phosphorylation of phosvitin have been delineated.99 Phosphorylated forms of phosphofructokinase100 and fatty acid synthetase101 have been discovered recently both may be concerned with the regulation of their respective enzymes. 

Mukhopadhyay, B. Field, R. A., A simple one-pot method for the synthesis of partially protected mono- and disaccharide bnilding blocks nsing an orthoesterification-benzylation-orthoester rearrangement approach. Carbohydr. Res. 2003,338,2149-2152. 

Lipson VV, Shirobokova MG, Shishkin OV et al (2006) Synthesis of partially hydrogenated pyrazolo[3, 4-b]quinolinones by condensation of 3-amino-5-methylpyrazole with aromatic aldehydes and dimedone. Russ J Org Chem 42(7) 1015-1021... 

The most striking feature of this reaction type is the simple formation of completely alkyl-substituted M - Sb heterocycles, which are hardly accessible by dehalosilylation and dehydrosilylation reactions due to the tendency of silylsubstituted dialkylstibines R2SbSiMe3 to undergo ligand exchange reactions at elevated temperatures, leading to the synthesis of partially silylsubstituted hetero cycles [28]. 

An interesting approach149 to the synthesis of partially protected nucleosides involved fusion for 12 hours at 130° of 5 -0-acetyladenosine and 2, 3, 5 -tri-0-acetyladenosine, followed by separation, by countercurrent distribution, of the so-formed mixture of 3, 5 -di-0-acetyl-, 5 -0-acetyl-, and 2, 3, 5 -tri-0-acetyladenosine. It is noteworthy that no 2, 5 -diester was isolated. A variation154 of this procedure was the fusion, at —200°, of a mixture of 2, 3, 5 -tri-0-acetyladenosine and adenosine, which yielded the 2, 3, 5 -triacetate, the 2, 3 -diacetate, and the 3, 5 -diacetate, with the last preponderating. 

This chapter describes the synthesis of partially fluorinated polyimides for optical teleconununications applications," " 2 their optical transparency (optical loss), refractive index, and birefringence properties" in addition to their fundamental properties. It also describes their device application as optical interference filters," " optical waveplates," and optical waveguides." -" ... 

Solid-Phase Synthesis of Partially Modified retro-inverso Peptides... 

Reetz et alJ33 described the stereoselective synthesis of partially protected a-hydroxy-y-amino acids 8 (Scheme 6) as potential pseudo-y-tum mimetics. X-ray diffraction structure analysis as well as NMR studies in CDC13 showed that these compounds display a pseu-docyclic eight-membered ring arising from an intramolecular H-bond between the amide carbonyl (i -1) and the alcohol hydroxy group (i). However, the ability of such a H-bond to induce or stabilize a pseudo-y-turn structure in an aqueous environment is doubtful. 

Kunz, H., Waldman, H., and Marz, J. (1989) Synthesis of partial structures of A-glycopeptides representing the linkage regions of the transmembrane neuraminidase of an influenza virus and of factor B of the human complement system. Liebigs Ann. Chem. (1), 45 19. 

The use of cycloaddition reactions for the synthesis of partially reduced heterocyclic systems was shown to be an attractive approach to dihydrobenzimidazoles, dihydroquinazolines, and dihydro-//n-benzopurines (Scheme 14) <86JOC6i6>. The dihydroxylation of the Diels-Alder adduct dimethyl 3,6-dihydrophthalate (128) with 0s04 and NMO followed by protection of the diol as the iso-propylidene derivative afforded compound (129). Saponification, dehydration with ethoxyethyne, and rearrangement with TMS—N3 effected conversion to the substituted tetrahydroisatoic anhydride (130), and subsequent treatment with formamidine acetate yielded compound (131). The substituents at the 6,7-positions of compound (131) were not amenable, however, for annelation of an imidazole. 

RCM has become a major approach to the synthesis of partially unsaturated heterocycles with five-membered and larger rings (Scheme 67) <2004CRV2199>. 

The methods discussed in Section 4.2.1.4 can also be used in the synthesis of partially unsaturated heterocycles. 

Scheme 28 Synthesis of Partially Protected Bovine Pancreatic Trypsin Inhibitor (1-13)I 1...

By the sequential use of different enzymes, efficient synthesis of partially acylated disaccharides can be achieved. 6-0-acetyl glucal 5 (Scheme 4), prepared... 

Two methods for the first synthesis of partial amides (257), (258) and a partial amide ester (259) of etidronate have been developed (Figure 48). The preparation of 1,1-bisphosphonates from tris(trimethylsilyl)phosphite (260) and acid anhydrides (261) has been described. This synthesis allows a... 

Owing to their positive charge, 1,2-dithiolium cations are, of course, almost unreactive to electrophiles. On the other hand, their conjugate bases, such as 3-alkylidene-l,2-dithioles, react easily with electrophilic reagents such as aromatic aldehydes, dimethylformamide, and nitrous acid. Some of these reactions are useful for the synthesis of partially bonded compounds and have been described, for papers prior to 1970, in a previous review (Ref 2 pp. 181, 187, 193). 

SCHEME 3.37 Synthesis of partially esterified sucrose derivatives. 

Pozsgay, V, A simple method for avoiding alkylthio group migration during the synthesis of thioglycoside 2,3-orthoesters. An improved synthesis of partially acylated 1-thio-a-L-rhamnopyrano-sides, Carbohydr. Res., 235, 295-302, 1992. 

Volonterio, A., Bravo, P. and Zanda, M. (2000) Synthesis of Partially Modified Retro and Retroinverso [NHCH(CF3)]-Peptides. Org. Lett., 2, 1827-1830. 

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