Boron compounds, conjugate

This commoner type of reaction involves the attack of carbon or heteroatom nucleophiles onto carbonyl compounds, by direct or conjugate addition, and onto imines. Because we have just dealt with boranes we shall start with the reaction of allylic boron compounds with such electrophiles. You might strictly not call this nucleophilic attack. 

The empty 2/j,-orbital on boron interacting with the ji-electrons of the butadienylidene system in borole (5) is proved by the pronounced bathochromic shift in the visible spectrum compared with that of its pyridine adduct. This Ti-electron delocalization in boroles is destabilizing and produces a 471-electron antiaromatic system. The antiaromaticity is further evidenced by the rapidity of reactions that remove the 2p ,-orbital on boron from conjugation. These reactions include Lewis complexation, transition metal complexation, or borole ring opening reactions such as Diels-Alder addition, oxidation, and protodeboration. This removal of the antiaromaticity from borole results in transforming the compound to a typical, low reacting, sterically hindered arylborane. 

The concept of immobilizing diol compounds with a boronic acid conjugated support as a sort of heterogeneous protecting group strategy is the antipode of the diol-based supports described in Section 1.4.2. Examples of such boronic acid matrices include polystyryl boronic acid resins (120) [500-502], the cellulose-derived support 121 [503], the methacrylic polymer 122 [504], and the polyacrylamide-supported nitroarylben-... 

In this chapter, we present data on conjugates of polyhedral boron compounds with different tumor-targeting carriers that have been synthesized and evaluated as potential agents for BNCT. 

A. V. Orlova, L. O. Kononov. Synthesis of conjugates of polyhedral boron compounds with carbohydrates. Russ. Chem. Rev., 2009, 78, 629-642. 

Orlova, A. V. Zinin, A. L Malysheva, N. N. Kononov, L. O. Sivaev, I. B. Bregadze, V. I. Conjugates of polyhedral boron compounds with carbohydrates. 1. New approach to the design of selective agents for boron neutron capture therapy of cancer. Russ. Chem.BulL, Int. Ed. 2003, 52, 2766-2768. 

Orlova, A. V., Kondakov, N. N., Zinin, A. I. et al. 2006. A uniform approach to the synthesis of carbohydrate conjugates of polyhedral boron compounds as potential agents for boron neutron capture therapy. Russ. J. Bioorg. Chem. 32 P.568-577. 

Based on these data various conjugates with antitumor agents (daunomycin, methotrexate, GnRH antagonist ), boron compounds or radionuclides were prepared. Antitumor activity of Ac-[D-Trp D-Cpa ,... 

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