O-Mesylation

In contrast to the usual behavior, replacement of the mesyl group in 2 O mesyl-3-diallylaminodeoxy-a-D-altropyranoside by treatment with triethylamine trihydrofluonde leads to, because of neighboring-group participation, the fluori-nated product with retention of configuration [45] (equation 33)... 

Azauridine was also synthesized using the knowledge of the course of alkylation of 6-azauracil 2-methylmercapto derivatives (e.g., Section II,B,4,b). The 1-ribofuranosyl derivative obtained by reaction of the mercury salt of the 2-methylmercapto derivative with tri-O-benzoyl-jS-D-ribofuranosyl chloride on removal of the methyl-mercapto and then benzoyl groups yielded crystalline 6-azauridine, The main difference between uracil and 6-azauracil nucleosides consists in the preparation of cyclic nucleosides. It is known that uridine can be readily converted to cyclic nucleosides by the reaction of 2 (50-O-mesyl derivatives with nucleophilic agents, Analogous... 

Deoxy-3 -fluorothymidine (813), a selective inhibitor of DNA synthesis, was prepared " in moderate yields from 3 -0-mesyl- or 3, 5 -di-O-mesyl-thymidine, through 2,3 -anhydro-1 -(2-deoxy- -D-t/2reopentofur-anosyl)thymine (808), by treatment with hydrogen fluoride (0.1% HF in l,4-dioxane-AlF3, 3.764 hf in DMF-AlFj, or 10% HF in DMF ),... 

Glycals are also available from 2-deoxy sugars by acid- or base-induced eliminations ofanomeric substituents. These methods are limited by the availability ofthe 2-deoxy sugars, for which the glycals themselves are the most obvious synthetic precursors. However, examples of these methods (Scheme 5.43) are in the direct preparation oftri-O-benzyl-D-glucal (14) from 2-deoxy-tri-O-benzyl-D-glucopyranose (13) via its 1-O-mesylate [117], and di-O-benzyl-D-ribal (16) from the phenylselenide 15 via oxidation to the selenoxide followed by elimination [118]. 

When allowed to react with sodium acetate in 2-methoxyethanol-water (9 1), de-O-mesylation takes place to yield a product (60), identical in all respects with the compound prepared from the waMMO-derivative (56) via N-acetylation (to (67)) and benzylidenation. However, since de-O-mesylation in (59) can occur either with participation of the nucleobase via the anhydronucleoside (62), or with participation of the acetamido group through the oxazoline (63), the steric relationship between C-2 and the branch point cannot be deduced unequivocally. Yet, when modifying the de-O-mesylation conditions to sodium methoxide/2-... 

Pankova and Tichy prepared all four stereoisomeric 4-rerr-butyl-2-aminomethyl-l-cyclohexanols and cyclized them with ethyl benzimidate to hexahydro-l,3-benzoxazines 158-161 (74CCC1447). From the A-acyl O-mesylate derivatives 162 and 163 on thermal cyclization or thionyl chloride treatment, ring closure occurred with inversion and resulted in 158 and 159 (74CCC1447). 

The latter reaction set up the possibility of making such exotic derivatives as 2,3-anhydro-4-chloro-talo-sucrose (Scheme 13) by a four-step sequence involving O-mesylation of 3,6,l, 3, 4, 6 -hexa-0-pivaloylsucrose, high-temperature LiCl displacement, O-depivaloylation with concomitant epoxide formation, and finally O-acetylation. 

The evident interest attending this method of bromination was reinforced by the observation that the reaction may be conducted in the presence of a wide range of other groups that are unaffected under these conditions (for instance, O-mesyl, -tosyl, -acetyl, -benzoyl, and -methyl groups, and a-epoxides).116... 

If 5-bromo-2,5-dideoxy-D-f/ireo-pentono- 1,4-lactone (7) was treated with aqueous potassium hydroxide and subsequently acidified, 2-deoxy-L-erythro-pentono-1,4-lactone (2-deoxy-L-ribonolactone) (12) (Scheme 4) was formed, and isolated as the crystalline di-O-benzoate [14]. Similarly, when 5-O-mesyl-... 

The cyclization of a peptide with an N-terminal 3-hydroxy-a-amino acid is generally performed via the O-mesyl or O-tosyl derivatives. Again the course of the cyclization reaction is governed by the N-terminal protecting group and best results are obtained with Al-trityl protected seryl/threonyl peptides. 

Gross and Oriez125 reported the synthesis of 4-S-acetyl-6-deoxy-4-thio-D-altrose (302) and 4-S-acetyl-6-deoxy-4-thio-D-idose (303) by using, as starting materials, the corresponding thiocyanates prepared in 35% yield from the 4-O-mesyl derivatives 298 and 299 by Sn2 displacement with thio-... 

Di-O-mesyl-D-mannitol (46) can be converted under acidic conditions (Dowex 50W-X2 cation-exchange resin) by way of 1,4-anhydro-3-0-mesyl-D-talitol (47) into D-isoidide (49) in almost quantitative yield. On using triethylamine - water, 2,3 4,5-dianhydro-D-iditol (48) is formed from this, on treatment with an acid ion-exchanger, D-isoidide (49) is formed in only 20% yield (see Scheme 7). From these observations, it was decided5 7,98 that the 2,3 4,5-dianhydro isomer 48 cannot be an intermediate in the conversion of 46 into 49. Similar results were found for the reaction of 46 or 3,4-di-O-p-tolylsulfonyl-D-mannitol (p-CH3C6H4S02- instead of CH3S02-in 46) with barium methoxide in methanol.99... 

The corresponding 1-O-mesyl ester has been obtained24 by shaking a dry benzene solution of the same bromide with finely powdered silver meth-anesulfonate for two days at room temperature. 

---