Sodium cyanoborohydride, used

Rather than preforming the a-amino ketimines to be reduced, it is often advantageous to form in situ the more reactive iminium ions from a-aminoketones and primary amines or ammonium salts in the presence of the reducing agent, e.g., sodium cyanoborohydride. Use of this procedure (reductive amination) with the enantiopure a-aminoketone 214 and benzylamine allowed the preparation of the syn diamines 215 with high yields and (almost) complete diastereoselectivities [100] (Scheme 32). Then, the primary diamines 216 were obtained by routine N-debenzylation. Similarly, the diamine 217 was prepared using ammonium acetate. In... 

Sodium, with l-bromo-3-chloro-cyclobutane to give bicyclo [l.l.O]butane, 51, 55 Sodium amalgam, 50, 50, 51 Sodium amide, with 2,4-pentane-dione and diphenyliodonium chloride to give l-phenyl-2, 4-pentanedione, 51, 128 Sodium azide, 50, 107 with mixed carboxylic-carbonic anhydrides, 51, 49 Sodium borohydride, reduction of erythro-3-methanesulfony-loxy-2-butyl cyclobutanecar-boxylate, 51, 12 reduction of 2-(1-phenylcyclo-pentyl)-4,4,6-trimethyl-5,6-dihydro-1,3(4H)-oxazine to 2-(1-phenylcyclopentyl)-4,4, 6-trimethyltetrahydro-l,3-oxazine, 51, 25 Sodium cyanoborohydride, used... 

A variation of the classical reductive amination procedure uses sodium cyanoboro hydride (NaBH3CN) instead of hydrogen as the reducing agent and is better suited to amine syntheses m which only a few grams of material are needed All that is required IS to add sodium cyanoborohydride to an alcohol solution of the carbonyl compound and an amine... 

Reductive amination of AT-succinyl chitosan and lactose using sodium cyanoborohydride in a phosphate buffer (pH 6.0) for 6 days was suitable for the preparation of lactosaminated M-succinyl chitosan (Fig. 3). Over 10% of dose/g-tissue was distributed to the prostate and lymph nodes at 48 h postadministration in both chitosan and lactosaminated N-succinyl chitosan. The labeled lactosaminated M-succinyl chitosan was easily distributed into not only the liver but also prostate, intestine, preputial gland and lymph nodes [153]. 

Sodium borohydride is sometimes used in conjunction with CeCl3 (Luche s reagent).70 The active reductants under these conditions are thought to be alkoxyborohydrides. Sodium cyanoborohydride is a useful derivative of sodium borohydride.71 The electron-attracting cyano substituent reduces reactivity and only iminium groups are rapidly reduced by this reagent. 

The Hofmann degradation product 252 used for a synthesis of corynoline (254) was again a useful starting material for ( )-corydalic acid methyl ester (8). It was reduced with sodium cyanoborohydride to the trans derivative 10 as a major product, which was converted to 8 via acetal 268 and aldehyde 269 (143). 

An interesting procedure has been proposed for the synthesis of amylose-b-PS block copolymers through the combination of anionic and enzymatic polymerization [131]. PS end-functionalized with primary amine or dimethylsilyl, -SiMe2H groups were prepared by anionic polymerization techniques, as shown in Scheme 56. The PS chains represented by the curved lines in Scheme 56 were further functionalized with maltoheptaose oligomer either through reductive amination (Scheme 57) or hydrosilyla-tion reactions (Scheme 58). In the first case sodium cyanoborohydride was used to couple the saccharide moiety with the PS primary amine group. 

Gheorghe et al. make use of sodium cyanoborohydride as a hydride source in the synthesis of 5-arylpiperidines <06OL1653>. Kellehar and Kelly report the formation of a spiro -lactam using sodium borohydride in the key reductive animation step <06TL3005>. 

Add 10 pi of 5 M sodium cyanoborohydride in 1N NaOH (Aldrich) per ml of the macromolecule solution volume prepared in (1). Caution Highly toxic compound. Use a fume hood and be careful to avoid skin contact with this reagent. 

Glutaraldehyde is the most popular b/s-aldchydc homobifunctional crosslinker in use today. Flowever, a glance at glutaraldehyde s structure is not indicative of the complexity of its possible reaction mechanisms. Reactions with proteins and other amine-containing molecules would be expected to proceed through the formation of Schiff bases. Subsequent reduction with sodium cyanoborohydride or another suitable reductant would yield stable secondary amine... 

Figure 7.11 Oxidation of glycoproteins with periodate, such as glycosylated antibodies, results in the formation of aldehyde groups that can be used for conjugation to dendrimers containing amine groups. Reductive amination with sodium cyanoborohydride results in coupling via secondary (or tertiary) amine bonds.

In a fume hood, add 10 pi of 5M sodium cyanoborohydride (Sigma) per ml of reaction solution. Caution cyanoborohydride is extremely toxic. All operations should be done with care in a fume hood. Also, avoid any contact with the reagent, as the 5M stock solution is dissolved in 1 N NaOH. If a higher pH buffer was used for the Schiff base formation, then adjust the solution to pH 7.5 before adding the cyanoborohydride. 

Another route to the formation of a hydrazide on a surface is to use an aldehyde-containing particle (such as HEMA/acrolein copolymers) and subsequently modify the aldehydes to form hydrazone linkages with bis-hydrazide compounds, which then can be stabilized by reduction with sodium cyanoborohydride (Chapter 2, Section 5). The resulting derivative contains terminal hydrazides for immobilization of carbonyl ligands (see Figure 14.18). 

Aldehyde particles are spontaneously reactive with hydrazine or hydrazide derivatives, forming hydrazone linkages upon Schiff base formation. Reactions with amine-containing molecules, such as proteins, can be done through a reductive amination process using sodium cyanoborohydride (Figure 14.21). 

The conjugate may be stabilized by addition of a reductant such as sodium borohy-dride or sodium cyanoborohydride. Usually sodium cyanoborohydride is recommended for specific reduction of Schiff bases, but since the conjugate has already formed at this point, the use of sodium borohydride will both reduce the associated Schiff bases and eliminate any remaining aldehyde groups. Add sodium borohydride to a final concentration of lOmg/ml. Continue to react for 1 hour at 4°C. 

Hapten molecules containing aldehyde residues may be crosslinked to carrier molecules by use of reductive animation (Chapter 3, Section 4). At alkaline pH values, the aldehyde groups form intermediate Schiff bases with available amine groups on the carrier. Reduction of the resultant Schiff bases with sodium cyanoborohydride or sodium borohydride creates a stable conjugate held together by secondary amine bonds. 

Figure 20.8 Enzymes that are glycoproteins like HRP may be oxidized with sodium periodate to produce reactive aldehyde residues. Conjugation with an antibody then may be done by reductive animation using sodium cyanoborohydride.

---