Bio-organic Chemistry Dr. Supartono, M.S. Harjono, S.Pd. M.Si.

What is bio-organic chemistry? Biological chem? Chemical bio? Chemical Biology: “Development & use of chemistry techniques for the study of biological phenomena” (Stuart Schreiber) Biological Chemistry: “Understanding how biological processes are controlled by underlying chemical principles” (Buckberry & Teasdale) Bio-organic Chemistry: “Application of the tools of chemistry to the understanding of biochemical processes” (Dugas) What’s the difference between these??? Deal with interface of biology & chemistry

BIOLOGYCHEMISTRY Simple organics eg HCN, H 2 C=O (mono-functional) Biologically relevant organics: polyfunctional Life large macromolecules; cells—contain ~ 100, 000 different compounds interacting 1 ° Metabolism – present in all cell 2 ° Metabolism – specific species, eg. Caffeine CHEMISTRY: Round-bottom flask BIOLOGY: cell How different are they?

Exchange of ideas: Biology Chemistry Chemistry explains events of biology: mechanisms, rationalization Biology –Provides challenges to chemistry: synthesis, structure determination –Inspires chemists: biomimetics → improved chemistry by understanding of biology (e.g. enzymes)

Key Processes of 1° Metabolism Bases + sugars → nucleosides nucleic acids Sugars (monosaccharides) polysaccharides Amino acids proteins Polymerization reactions; cell also needs the reverse process We will look at each of these 3 parts: 1)How do chemists synthesize these structures? 2)How are they made in vivo? 3)Improved chemistry through understanding the biology: biomimetic synthesis

Properties of Biological Molecules that Inspire Chemists 1)Large → challenges: for synthesis for structural prediction (e.g. protein folding) 2)Size → multiple FG’s (active site) ALIGNED to achieve a goal (e.g. enzyme active site, bases in NAs) 3)Multiple non-covalent weak interactions → sum to strong, stable binding non-covalent complexes (e.g. substrate, inhibitor, DNA) 4)Specificity → specific interactions between 2 molecules in an ensemble within the cell

5) Regulated → switchable, allows control of cell → activation/inhibiton 6) Catalysis → groups work in concert 7) Replication → turnover e.g. an enzyme has many turnovers, nucleic acids replicates

Evolution of Life Life did not suddenly crop up in its element form of complex structures (DNA, proteins) in one sudden reaction from mono- functional simple molecules In this course, we will follow some of the ideas of how life may have evolved:

RNA World Catalysis by ribozymes occurred before protein catalysis Explains current central dogma: Which came first: nucleic acids or protein? RNA world hypothesis suggests RNA was first molecule to act as both template & catalyst: catalysis & replication

How did these reactions occur in the pre-RNA world? In the RNA world? & in modern organisms? CATALYSIS & SPECIFICITY How are these achieved? (Role of NON-COVALENT forces– BINDING) a) in chemical synthesis b) in vivo – how is the cell CONTROLLED? c) in chemical models – can we design better chemistry through understanding biochemical mechanisms?

Relevance of Labs to the Course Labs illustrate: 1)Biologically relevant small molecules (e.g. caffeine ) 2)Structural principles & characterization (e.g. anomers of glucose, anomeric effect, diastereomers, NMR) 3)Cofactor chemistry – pyridinium ions (e.g. NADH) 4)Biomimetic chemistry (e.g. simplified model of NADH) 5)Chemical mechanisms relevant to catalysis (e.g. NADH)

6)Application of biology to stereoselective chemical synthesis (e.g. yeast) 7)Synthesis of small molecules (e.g. drugs, dilantin, tylenol) 8)Chemical catalysis (e.g. protection & activation strategies relevant to peptide synthesis in vivo and in vitro) All of these demonstrate inter-disciplinary area between chemistry & biology

Two Views of DNA 1)Biochemist’s view: shows overall shape, ignores atoms & bonds 2)chemist’s view: atom-by-atom structure, functional groups

Biochemist’s View of the DNA Double Helix Major groove Minor groove

Chemist’s View

BASES Aromatic structures: –all sp 2 hybridized atoms (6 p orbitals, 6 π e - ) – planar (like benzene) N has lone pair in both pyridine & pyrrole  basic (H + acceptor or e - donor)

6 π electrons, stable cation  weaker acid, higher pKa (~ 5) & strong conj. base sp 3 hybridized N, NOT aromatic  strong acid, low pKa (~ -4) & weak conj. base Pyrrole uses lone pair in aromatic sextet → protonation means loss of aromaticity (BAD!) Pyridine’s N has free lone pair to accept H+  pyridine is often used as a base in organic chemistry, since it is soluble in many common organic solvents

The lone pair also makes pyridine a H-bond acceptor e.g. benzene is insoluble in H 2 O but pyridine is soluble: This is a NON-specific interaction, i.e., any H-bond donor will suffice

Contrast with Nucleic Acid Bases (A, T, C, G, U) – Specific! Evidence for specificity? Why are these interactions specific? e.g. G-C & A-T

Evidence? –If mix G & C together → exothermic reaction occurs; change in 1 H chemical shift in NMR; other changes  reaction occurring –Also occurs with A & T –Other combinations → no change! e.g. Guanine-Cytosine: Why? –In G-C duplex, 3 complementary H-bonds can form: donors & acceptors = molecular recognition

Can use NMR to do a titration curve: Favorable reaction because ΔH for complex formation = -3 x H-bond energy ΔS is unfavorable → complex is organized  3 H-bonds overcome the entropy of complex formation **Note: In synthetic DNAs other interactions can occur

Molecular recognition not limited to natural bases:  Create new architecture by thinking about biology i.e., biologically inspired chemistry! Forms supramolecular structure: 6 molecules in a ring

Synthesis of Bases (Nucleic) Thousands of methods in heterocyclic chemistry– we’ll do 1 example: –May be the first step in the origin of life… –Interesting because H-CN/CN - is probably the simplest molecule that can be both a nucleophile & electrophile, and also form C-C bonds

Mechanism?

Other Bases? ** Try these mechanisms!

Properties of Pyridine We’ve seen it as an acid & an H-bond acceptor Lone pair can act as a nucleophile:

Balance between aromaticity & charged vs non-aromatic & neutral!  can undergo REDOX reaction reversibly:

Interestingly, nicotinamide may have been present in the pre-biotic world: NAD or related structure may have controlled redox chemistry long before enzymes involved! electical discharge CH 4 + N 2 + H 2

Another example of N-Alkylation of Pyridines This is an S N 2 reaction with stereospecificity

References Solomons Amines: basicity ch.20 –Pyridine & pyrrole pp –NAD + /NADH pp 645-6, 537-8, Bases in nucleic acids ch. 25 Also see Dobson, ch.9 Topics in Current Chemistry, v 259, p 29-68