NaOH- NaBH4 treatment

Removal of the oligosaccharide chain from the glycoprotein usually involves the use of one of three main methods treatment with NaOH-NaBH4, hydrazinolysis, or proteolysis.34-36 The NaOH-NaBH4 treatment is used to release, somewhat specifically, oligosaccharides O-linked to serine and threonine. Hydrazinolysis is used to break N-linkages, and proteolysis, to isolate glycopeptides. Each method apparently still has some drawbacks. 

Reduction of the nitroaromatic with NaBH4 in DMSO or Zn in NaOH/EtOH leads to the hydrazo derivative and treatment with aqueous HC1 gives benzidine rearrangement.115... 

By treatment with NaBH4 in aqueous NaOH in the presence of dithienyl ditelluride, a-phenylseleno carboxylic esters and malonates, as well as a-phenylseleno carboxylic acids, are deselenylated to the corresponding seleno-lree acids in good yields. The selective removal of the seleno group without dealkylation of the ester moiety is achieved by the methods depicted in the scheme. 

Diazomethane is generated by the reaction of aqueous NaOH with N-methyl-N-nitroso-p-toluenesulfonamide (Diazald ) in DMSO. The diazomethane is generated quantitatively and is removed by a stream of N2 into a packed column containing a stream of mixed anhydride formed from an N-protected (BOC or CBZ) amino acid and ethyl chloroformate. The diazoketone is converted to the chloroketone using HCI, as shown in Scheme 11.10. The chiral epoxide can then be formed via diastereoselective reduction with NaBH4 and treatment with base. 

When ester 206 (R = Et) was hydrolyzed with 10% aqueous NaOH in EtOH gave 1 1 mixture of diastereomeric 6-acids 206 (R = H) in 65% yield [08H(75)1497]. Alternatively, hydrolysis with LiOH afforded a mixture of acid 206 (R = H). The major isomer was treated with ClCC Et to give a mixed anhydride, which was reduced with NaBH4 to furnish 1 5 mixture alcohols 207 and 208. The alcohol 208 was transformed into 6-iodomethyl derivative 209 (R = I) by treatment with (PhO)3P MeI in 87% yield, which was catalytically hydrogenated over Pd/C catalyst in the presence of NaOAc in MeOH to yield 6-methyl derivative 209 (R = H) quantitatively. 

CycUzation of isoprenoids.1 Acyclic isoprenoids can be cyclized in 30-60% yield by treatment with 1.2-2.0 eq. of mercuric trifluoroacetate in nitromethane or acetonitrile at -20° to 0°. After 5- 30 min. the reaction mixture is treated with 2 eq. of NaBH4 in 3 M NaOH solution at 0°. An example is the cyclization of trans-geranylacetone (1) to 2,5,5,9-tetramethylhexahydrochromene (2). 

NaBH4/NaOH treatment yields 5,6-dihydroxyindole-2-carboxylic acid... 

In the presence of a proximal alcohol the aminal is isolated upon DDQ treatment. This can be cleaved by treatment with NaOH followed by NaBH4. ... 

Treatment of the diacetoxymercuri compound 45 with NaBH4 in aqu. NaOH-solution gave only 23% of unsubstituted N(6)-phenylsulfonyl-2-oxa-6-aza-ada-... 

A soln. of L-valine in 2 N NaOH vigorously stirred, treated with benzaldehyde, after 15-20 min. NaBH4 added below 15°, stirring continued 0.5 hr., the treatment with benzaldehyde and NaBH4 repeated, finally stirred 2 hrs. N-benzyl-L-valine (Y 86%) heated 1.5 hrs. on a steam bath with formic acid and 38-40%-formaldehyde soln. N-benzyl-N-methyl-L-valine (Y 92%) dissolved in 90%-acetic acid, and hydrogenated with 5%-Pd-on-carbon N-methyl-L-valine (Y ... 

---