T

tunicamycin V

capuramycin

NAD+

Figure 3.4. Structure of nucleoside cofactors ATP and NAD.

Figure 3.4. Structure of nucleoside cofactors ATP and NAD.

Figure 3.5. General procedures for N-glycoside formation. Acetate (CH3CO-)

(2) Aqueous NH3, dioxane.

Figure 3.6. Common ribose protecting groups.

Toluyl (p-MePhCO-)

OTol

cleavage: NH3, MeOH, 100oC, 78%. Pivaloyl (Me3CCOCl )

i) Piv-Cl, pyridine. cleavage: NaOMe, MeOH.

Benzyl (PhCH2-)

Tertbutyldimethylsilyl (tBuMe2Si-)

cleavage: H2/Pd(OH)2, EtOH.

l/ON

cleavage: (1) tetrabutylammonium fluoride (TBAF). (2) pTsOH, MeOH, H2O, 7h.

iPr2SI

iPr2Si—0

iPr2SI

i) Pr2iSi(Cl)0Si(Cl)Pr2i, imidazole, THF, rt, 90 min.

cleavage: Bu4NF, THF. Figure 3.6. (continued)

porcine liver esterase (PLE), affording pure p-anomer thymidine in 29 and 31%, respectively (Figure 3.10).20

When porcine pancreas lipase (PPL) in phosphate buffer is used for deacetylation of 3',5'-di-O-acetylthymine, the removal of the acetyl group at the 5'-position is achieved, leading to the 3'-O-acetylthymidine (Figure 3.11).20

Other suitable selective protections and deprotections useful for chemical manipulations that might occur at the ribosyl moiety are illustrated in Figure 3.12.

OH X

OH X

i) Subtilisin 8350, DMF. 65-100% O

AcO B

OH X

OH X

CO2H

CO2H

i) Pseudomona cepacea lipase, RCO2Et, AcOEt, rt, 72h. Figure 3.7. Enzymatic regioselective acylation by oximeacetates and lipases.

HO B

HO B

i) Pseudomona cepacea llipase (PSL), Pyridine. ii) Candida antartica lipase (CAL), THF. Figure 3.7. (continued)

R.JO OH

OH OH

OH OH

0 0

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