Biotin is a white crystalline vitamin that is fairly stable when dry but can degrade in acidic or basic solutions. It has an essential chemical structure consisting of a planar ureido nucleus joined to a folded tetrahydrothiophene nucleus. Of its eight possible stereoisomers, only the d-isomer possesses biological activity. Biotin functions as a coenzyme by forming a covalent bond between its thiophane nucleus and the lysine residue of enzymes. Its ureido nucleus can become polarized and activated, increasing its nucleophilicity to allow biotin to transport carbon dioxide by binding the electrophilic carbonyl phosphate formed from bicarbonate and ATP.

1. Chemical and physical
properties of biotin
Domina Petric, MD

2. Essential features of the chemical
structure:
Conjoined ureido and
tetrahydrothiophene nuclei
Ureido 3′ nitrogen is sterically
hindered, preventing substitution
Ureido 1′ nitrogen is poorly
nucleophilic
April 18, 2018
Combs GF. The Vitamins. Fundamental Aspects in
Nutrition and Health. Elsevier Inc. 2008.
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3. Biotin nomenclature
• Biotin is the trivial
designation of the compound
cis-hexahydro-2-oxo-1H-
thieno[3,4-d]imidazole-4-
pentanoic acid, also known
as vitamin H, vitamin B7 and
coenzyme R.
April 18, 2018
Combs GF. The Vitamins. Fundamental Aspects in
Nutrition and Health. Elsevier Inc. 2008.
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4. Chemical and physical properties
Biotin is a white crystalline
substance that, in dry form, is
fairly stable to air, heat and light.
In solution, it is sensitive to
degradation under strongly
acidic or basic conditions.
April 18, 2018
Combs GF. The Vitamins. Fundamental Aspects in
Nutrition and Health. Elsevier Inc. 2008.
4

5. Chemical and physical properties
• Its structure consists of a planar
ureido nucleus and a folded
tetrahydrothiophene (thiophane)
nucleus, which results in a boat
configuration with a plane of
symmetry passing through the S-1,
C-2′, and O positions in such a way
as to elevate the sulfur atom above
the plane of the four carbons.
April 18, 2018
Combs GF. The Vitamins. Fundamental Aspects in
Nutrition and Health. Elsevier Inc. 2008.
5

6. Chemical and physical properties
The molecule has three
asymmetric centers.
Of the eight possible
stereoisomers, only the (+)-
isomer (called d-biotin) has
biological activity.
April 18, 2018
Combs GF. The Vitamins. Fundamental Aspects in
Nutrition and Health. Elsevier Inc. 2008.
6

7. Chemical and physical properties
• Biotin is covalently bound to its
enzymes by an amide bond to the
ε-amino group of a lysine residue
and C-2 of the thiophane nucleus.
• This bond is flexible, allowing the
coenzyme to move between the
active centers of some enzymes.
April 18, 2018
Combs GF. The Vitamins. Fundamental Aspects in
Nutrition and Health. Elsevier Inc. 2008.
7

8. Chemical and physical properties
• The biotin molecule is activated by
polarization of the O and N-1′ atoms of
the ureido nucleus.
• This leads to increased nucleophilicity at
N-1′, which promotes the formation of a
covalent bond between the electrophilic
carbonyl phosphate formed from
bicarbonate and ATP, and allows biotin to
serve as a transport agent for CO2.
April 18, 2018
Combs GF. The Vitamins. Fundamental Aspects in
Nutrition and Health. Elsevier Inc. 2008.
8

9. Literature
• Combs GF. The Vitamins. Fundamental Aspects in
Nutrition and Health. Elsevier Inc. 2008.
April 18, 2018 9