Henk Buck
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Professor Henk Buck (1930) studied at the University of Leiden where he received his PhD in 1959. He became a lectorship at the University in Theoretical Organic Chemistry in 1965. For his research he got the Golden Medal of the Royal Netherlands Chemical Society in 1967. In 1970 he was appointed to professor of Physical Organic Chemistry and Organic Chemistry at the University of Technology in Eindhoven. Because there was no Chair for Theoretical Chemistry and Biochemistry he gave lectures in organic chemistry, physical organic chemistry, theoretical organic chemistry, biochemistry and biotechnology. From 1988-1991 he was Dean of the Chemical Faculty. For his scientific contributions he became member of the Royal Netherlands Academy of Arts and Sciences in 1979. During his scientific career he published more than 300 scientific papers spread over a large area of the chemical field. Under his supervision 43 chemical engineers became their PhD [1].
His research in Leiden and later in Eindhoven was focused on organic chemistry as the homogeneous catalysis of the oxidation of hydrocarbons with stable carbenium ions as the pentamethylbenzyl cation [2] and the chiral induction with the redox couple NADH-NAD+ in the nearly 100% stereospecific hydride transfer to ketones and imines [3]. The latter process is controlled by the out-of-plane orientation of the carboxamide group [4]. In the field of physical chemistry his work was directed on electron spin resonance measurements of phosphoranyl radicals with phosphorus in different geometries as the tetrahedral and the trigonal bipyramidal configuration with the unpaired electron in an equatorial or axial orientation [5]. His contribution to the theoretical organic chemistry was based on ab initio calculations of the radiationless transition of formaldehyde [6] and ab initio calculations of single vibronic level fluorescence emission spectra and absolute radiative lifetimes of formaldehyde [7]. Further he investigated deviations of the Woodward-Hoffmann rules as the photochemical [1,3]-OH shift in 2-propen-1-ol [8]. Here the stereochemical outcome is determined by relaxation of the excited double bond. A thermal study of the cis-[1,5]-H shifts in 1,3-pentadiene showed the effect of vibrationally assisted tunneling in this geometric orientation [9].
A special topic in his research was the organophosphorus chemistry. An important aspect of this project was based on the possibility of phosphorus (IV) to accommodate a fifth ligand under formation of a trigonal bipyramid which shows a number of unique properties. The significance of this geometrical change has been demonstrated in the conformational transmission in DNA for the B-Z transition with alternating CpG units under selective phosphate shielding [10]. This change in geometry of phosphorus was also applicable on the biochemical dynamics of cAMP [11]. Because of the importance of shielding, the OCH3 group was introduced as substitute for O– in the study of intermediates for conformational transmission. This also resulted in the synthesis of phosphate-methylated DNAs and RNAs. Methylphosphotriester DNAs were synthesized with 2-12 bases. Neutralization of the charge of the phosphate linkages by (specific) methylation resulted in methylphosphotriester DNAs with very exclusive (bio)chemical properties [12]. The introduction of chirality at phosphorus appeared of importance for intra- and intermolecular dynamics. These modified DNAs mimiced the behavior of natural DNA in the absence of stabilizing factors as salts, proteins, and medium factors. In fact a high site-specific hybridization affinity was obtained with complementary natural DNA. In dependence of the bases, parallel DNA could be synthesized for pyrimidine bases in which the chirality of phosphorus was decisive [13]. Phosphate methylation also gave the possibility to synthesize a self-complementary left-handed Z-DNA mini duplex.
After he and his co-workers published in Science the interruption of the life cycle of the human immunodeficiency virus type-1 with phosphate-methylated DNA (Science,13 April 1990) [14], there raised criticism. This resulted in a three-men investigation committee of the Chemical Faculty and later in a two-men investigation committee of the University. Although both panels had no experience in organic chemistry they were particularly critical of the synthesis and the nuclear magnetic resonance spectrum of the alleged modified DNA. They described the nuclear magnetic resonance spectrum as highly atypical and anomalous and selected from a large set of unusuable measurements and concluded that its publication certainly bordered on fraud [15]. Because of accusations he was pressed to retract his work [16] and took early retirement. From the documents available it is now clear that the scientific judgement in the reports is in error [17].
At home without any academic support he wrote several articles based on quantum chemical calculations focused on the dynamics of organic reactions, electron spin resonance of organophosphorus radicals and the hybridization affinity of methylphosphotriester DNA and RNA. The latter subject is published as review articles in Nucleosides, Nucleotides & Nucleic Acids. In these reviews he gives also a thorough description and explanation of the chemical and corresponding biochemical results of the methylphosphotriester DNA, RNA and related systems. This contribution that is mainly based on the work at Eindhoven also consists of new insights in solid-phase synthesis, B-Z transition, and methyl transfer reactions connected with replicational and transcriptional silencing. Special attention is given to the effect of phosphate shielding on duplex stability. Models based on molecular mechanics calculations and recent density functional ab initio calculations support the impact of phosphate shielding at the various levels of stability of the DNA duplex.
References
1.Henk Buck: A dutch chemist; see: Wikipedia(dutch).
2.Van Pelt, P. et al. (1976) "Proton acid catalyzed hydride transfer from alkanes to methylated benzyl cations. Part III: Solvated alkanes as Hydrogen-donating intermediates", Journal of the American Chemical Society,Vol. 98, pp. 5864-5870.
3.Vekemans, J.A.J.M. et al. (1991) "NADH model mediated reduction of C=N substrates: enantioselective synthesis of D-and L-phenylglycinates",Thetrahedron: Asymmetry, Vol.2, pp. 949-952.
4.Donkersloot, M.C.A. et al.(1981) "The hydride-donation reaction of reduced nicotinamide adenine dinucleotide. 2.MINDO/3 and STO-3G calculations on the role of the CONH2 group in enzymatic reactions", Journal of the American Chemical Society, Vol. 103, pp. 6554-6558.
5.Aagaard, O.M. et al. (1990) "Intermolecular effects on the radiogenic formation of electron-capture phosphorus-centered Journalradicals A single-crystal ESR study of diastereoisomeric precursors", Journal of the American Chemical Society, Vol. 112, pp. 938-944.
6.Van Dijk, J.M.F. et al. (1978) "Ab initio CI calculation of the radiationless transition of the 1(npi)state of formaldehyde", Journal of Chemical Physics, Vol. 69, pp. 2462-2473.
7.Van Dijk, J.M.F. et al. (1978) "Ab initio CI calculation of single vibronic level fluorescence emission spectra and absolute radiative lifetimes of H2CO(1A2)", Journal of Chemical Physics, Vol. 70, pp. 2854-2858.
8.Dormans, G.J.M. et al. (1984) "A quantum chemical study on the mechanism of a photochemical {1,3]-OH shift in 2-propen-1-ol", Journal of the American Chemical Society, Vol. 106, pp. 1213-1216.
9.Dormans, G.J.M. et al. (1984) " Mechanism of the thermal [1,5]-H shift in cis 1,3-pentadiene. Kinetic isotope effect and vibrationally assisted tunneling", Journal of the American Chemical Society, Vol. 106, pp. 3253-3258.
10.Van Lier, J.J.C. et al. (1983)"B-Z transition in methylated DNA. A quantum-chemical study", European Journal of Biochemistry, Vol. 132, pp. 55-62.
11.Broeders, N.L.H. et al. (1990)"A 400- and 600- MHz 1H NMR conformational study on nucleoside cyclic 3',5'PV-TBP systems. Conformational transmission induces diequatorial orientation of the 3',5'-dioxaphosphorinane ring in a nonchair conformation", Journal of the American Chemical Society, Vol. 112, pp. 7475-7482.
12.European Patent entitled Poly(deoxyribonucleotides), pharmaceutical compositions, use and preparation of the poly(deoxyribonucleotides) München 09-06-1993, Patent NO. 0358657.
13.Koole, L.H. et al. (1987) "A parallel right-handed duplex of the hexamer d(TPTPTPTPTPT) with phosphate triester linkages",Journal of the American Chemical Society, Vol. 109, pp. 3916-3921.
14.Buck, H.M. et al. (1990) "Phosphate-methylated DNA aimed at HIV-1 RNA loops and integrated DNA inhibits viral infectivity", Science, Vol. 248, pp. 208-212.
15.Hagendijk, R. et al. (1993) "Blind faith: fact, fiction and fraud in public controversy over science", Public understanding science, Vol. 2, pp. 391-415.
16.Moody, H.M. et al. (1990)"Inhibition of HIV-1 infectivity by phosphate-methylated DNA: retraction", Science, Vol. 250 pp. 125-126.
17.Buck, H.M. (2004) "The chemical and biochemical properties of methylphosphotriester DNA", Nucleosides, Nucleotides Nucleic Acids, Vol. 23, pp. 1833-1847.
