Deoxygenated derivatives, preparation

In the early 1990s, the Bartons protocol was widely applied to the preparation of deoxygenated derivatives at many sites on taxanes. Enhancement of cytotoxicity was observed for many 7-deoxy paclitaxel and docetaxel analogs, along with a... 

Linear Homotetrasaccharides - Cellulose oligomers up to the 20-mer have been assembled from a key tetrasaccharide glycoside which was converted into the glycosyl trichloroacetimidate and separately to a derivative with 0-4 of the non-reducing end deprotected. Several specifically deoxygenated derivatives of P-maltosyl-(l- 4)-a,a-trehalose have been specifically prepared, sulfated and tested for smooth muscle cell antiproliferative activity. Iterative methods have been applied to make the a-(l ->2)-D-mannose tetramer and di- to tetra-... 

Elimination reactions of 2 -deoxynucleosides have been used to prepare 2, 3 -didehydrodideoxy derivatives of cytosine (d4C), and hence ddC, some 6-azapyrimidine nucleosides,and some indole nucleosides. A thermal elimination on a 3 -phenylselenoxide was a key step in a streamlined procedure for making d4T from thymidine in a three-pot sequence. Various deoxygenated derivatives of ribavirin have been reported, and d4T has been prepared radiolabelled at C-2. ... 

As another example of nitrene formation, the reaction of o-nitrostilbene (96) with CO in the presence of SnCU affords 2-phenylindole (97). The reaction is explained by nitrene formation by deoxygenation of the nitro group with CO, followed by the addition of the nitrene to alkene. Similarly, the 2//-indazole derivative 99 was prepared by reductive cyclization of the A-(2-nitrobenzyli-dene)amine 98[89]. 

Stereospecific deoxygenations in the cryptophycin family of natural products from Nostocaceae were reported by Moore [47]. The products were important in the elucidation of the natural product s structure and for the preparation of novel cryptophycin derivatives. 

Derivatives 47-51 were prepared from the iV-oxide 46 using zinc as the deoxygenating agent (Scheme 11). The use of Zn in NH4CI solution led to the deoxy derivatives 47 and 48 in moderate yields. The reduction was clearly observed by NMR HETCOR experiments (HMQC and HMBC). When the reduction of the derivative 46 (R = CH2C1) was carried out under the same conditions, compound 51 was generated via a Zn-promoted reductive dimerization process <2001EJM771>. 

The bridged 1,4-dioxepanones 112 (R = TBMS X = H, Me) were prepared, unexpectedly, in moderate yield by radical deoxygenation of capuramycin derivatives. These products were rationalised in terms of a novel intramolecular radical glycosylation-lactonization reaction <00H(52)133>. 

Preparation of the pioneering manganese(I) allenylidene derivatives [MnCp(=C= C=CR2)(C0)2] (5) was accomplished by treatment of the Ti-aUcyne complex [MnCp ( 7 -HC=CC02Me)(C0)2] (4) with excess of an organolithium reagent, followed by deoxygenation with HCl or COCI2 (Scheme 5) [24,42,95]. In essence, this reaction... 

Coriolin (689), a metabolite of the Basidiomycete Coriolus consors, has attracted widespread interest because of its unusual anti-tumor activity and highly functionalized triquinane structure. Accordingly, a number of syntheses of689 have appeared on the scene. One of the earliest, due to Tatsuta, et al., begins with epoxide 690, whose preparation had been earlier realized in connection with their work on hirsutine (see Scheme LXIII). Deoxygenation of 690, hydrolysis, and cis-hydroxy-lation provided keto triol 691 (Scheme LXXII) The derived acetonide was transformed via 692 into tetraol 693 which could be selectively acetylated and dehydrated on both flanks of the carbonyl group. Deacetylation of 694 followed by epoxidation completed the synthesis. 

Functionalized zinc carbenoids have been prepared from carbonyl compounds by an indirect strategy. The deoxygenation of a carbonyl compound to an organozinc carbenoid can be induced by a reaction with zinc and TMSCl. Therefore, the aldehyde or ketone, when treated with TMSCl or l,2-bis(chlorodimethylsilyl)ethane in the presence of an alkene, generates the cyclopropanation product. This method is quite effective for the production of alkoxy-substituted cyclopropane derivatives. A 55% yield of the... 

Table III gives preparations of six-, seven-, and eight-carbon ketoses, and their methylated, deoxygenated, azido, amido, and branched-chain derivatives. All these are first obtained as ketose phosphates, but this is not a severe restriction, for, apparently, enzymic hydrolysis with phosphatases is always successful. Phosphatases constitute a versatile group of enzymes, easily...

Photochemical deoxygenation of the 3-0-pivaloyl derivative 126 was also used for the preparation of the methyl ascaryloside (119) (Scheme 36).205... 

L-Rhodinose (174) was prepared from the readily available L-rhamnose.269 The method required deoxygenation of C-2 and C-3 and inversion of configuration at C-4 (Scheme 56). Oxidation of 187 with ruthenium dioxide-IOj, followed by reduction of the keto groups with lithium aluminum hydride yielded the alcohol 188. After protection as the benzyl derivative, an alkenic linkage was... 

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