O-mesyl derivatives

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... 

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). 

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-... 

Very little of this deacetonated material was obtained when the corresponding 5,6-O-mesyl derivative (compound 4) was treated411 in the customary manner. As regards compound 6 (Table VIII), the procedure of Karrer and Davis216 led to partial acetonation ... 

Reaction with methyl D-glycopyranosides11 1, 664, before references]. Mesyl chloride (2 equiv.) reacts with methyl a-D-glucopyranoside in DMF with selective replacement of the primary alcoholic group by chlorine to give a 6-chloro-6-desoxy-hexopyranoside. The 6-O-mesyl derivative is not an intermediate. In the case of methyl u-D-xylopyranoside (no primary hydroxyl group), 99% of unchanged glycoside was recovered from the reaction. 

When starting from the per-O-mesylated derivative 7 the reaction only proceeded through C-6 to form the corresponding 1,6-anhydro-iminosugar 8 (Scheme 3) and no reaction was observed through C-4 [41],... 

Catalytic reduction of the 3 -azido-3 -deoxy-2-O-mesyl derivative prepared from 2 ,3Wnhydro-adenosine yielded an 2 ,3 -aziridine of inverted (lyxo) con-... 

O-isopropylidene derivative (57) must exist in pyridine solution in a conformation which favors anhydro-ring formation rather than elimination. Considerable degradation occurred when the 5-iodo derivative (63) was treated with silver fluoride in pyridine (36). The products, which were isolated in small yield, were identified as thymine and l-[2-(5-methylfuryl)]-thymine (65). This same compound (65) was formed in high yield when the 5 -mesylate 64 was treated with potassium tert-hx Xy -ate in dimethyl sulfoxide (16). The formation of 65 from 63 or 64 clearly involves the rearrangement of an intermediate 2, 4 -diene. In a different approach to the problem of introducing terminal unsaturation into pento-furanoid nucleosides, Robins and co-workers (32,37) have employed mild base catalyzed E2 elimination reactions. Thus, treatment of the 5 -tosylate (59) with potassium tert-butylate in tert-butyl alcohol afforded a high yield of the 4 -ene (60) (37). This reaction may proceed via the 2,5 ... 

Some simplified assumptions for extracting interproton relaxation-contributions from a single set of nonselective relaxation-rates have been made for a tetrachlorotetra-0-mesyl-ga/ac(o-sucrose derivative (43). By con-... 

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-... 

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. 

Quite analogous ring-closures occur when the 1-O-acetyl derivatives of the rhamnopyranose and talopyranose derivatives are treated with sodium azide in N,N-dimethylformamide. l-O-Acetyl-6-deoxy-2,3-0-isopropylidene-4-0-mesyl-a-L-mannopyranose is converted exclusively into l,4-anhydro-6-deoxy-2,3-0-isopropylidene-/3-L-talo-pyranose. In this instance, the azide nucleophile attacks the l-O-ace-tyl group, liberating an 0-1 oxide ion which reacts with inversion of C-4. The 4-epimeric, l-O-acetyl-6-deoxy-talose derivative gives 60% of the direct inversion product l,4-anhydro-6-deoxy-2,3-0-isopropyli-dene-a-L-mannopyranose, together with other products.50... 

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. 

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