The molecular geometry of Halomon in the ground state has been calculated by B3LYP/ 6-31G(d, p) and MP2/6-31G(d, p) methods. An examination of its structure suggests that rotation around a single bond between C3-C9 and C6-C7 is not quite free due to steric factor. The Br atom present at C9 and the bulky group –(CH2)2-CHBr-CCl(CH3)2 present at C3 are oppositely directed (anti). The Cl atom attached to C7 and the –CH2- CH2- group present at C6 are gauch to each other. For the optimized structure, the standard thermodynamic functions have been calculated, and the harmonic vibrational frequencies for Halomon are calculated at the B3LYP/6-31G(d, p).

Halomon (6(R)-Bromo-3(S)-(Bromomethyl)-7-Methyl-2,3,7-Trichloro-1-Octene) is a polyhalogenated acyclic monoterpene, which was first obtained from the red alga, Portieria hornemannii (Fuller et al., 1992). Halomon exhibited highly differential cytotoxicity invitro against brain tumor, renal and colon tumor cell lines in the National Cancer Institute’s screen (Fuller et al., 1994; Egorin et al., 1996 and 1997; Jung and Parker, 1997 and Sotokawa et al., 2000). Recent research has shown that Halomon is an inhibitor of the enzyme DNA Methyl Transferase-1 (DNMT-1), which is responsible for methylation by catalyzing the transfer of a methyl group from S-Adenosylmethionine to the 5/ position on Cytosine phosphodiester-linked Guanine dinucleotide (CpG) sites. In many cancers, hypermethylation at CpG sites silence the promoters of tumor suppressor genes. Thus, the inhibition of DNMT-1 could potentially reverse tumor growth (Yoo et al., 2002; and Andrianasolo et al., 2006). The molecular structure of Halomon is given in Figure 1.

An investigation of the three aspects of Halomon were undertaken in the present study: Structural study of Halomon with the ab-initio and Density Functional Theory (DFT), calculation of thermodynamic properties of Halomon by B3LYP/6-31G(d, p) method, and harmonic vibrational frequency calculation at the B3LYP/6-31G (d, p) level.

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