Which of the following is correct structure of `alpha`-anomer of maltose ?

Options

A.
B.
C.
D.

Answer

To determine the correct structure of the alpha-anomer of maltose, we can follow these steps:

### Step 1: Understand the Structure of Maltose
Maltose is a disaccharide composed of two glucose units. The linkage between these glucose units is an alpha 1,4-glycosidic bond.

### Step 2: Draw the Open Chain Structure of Glucose
Start by drawing the open-chain form of glucose. The structure of glucose in its open-chain form is:

```
CHO
|
H-C-OH
|
HO-C-H
|
H-C-OH
|
H-C-OH
|
CH2OH
```

### Step 3: Convert to the Cyclic Form
Glucose can cyclize to form a six-membered ring (pyranose form). The hydroxyl group (OH) on the first carbon can react with the aldehyde group to form a hemiacetal.

### Step 4: Identify the Anomeric Carbon
In the cyclic form of glucose, the anomeric carbon is the first carbon (C1). For the alpha-anomer, the hydroxyl group on this carbon is positioned below the plane of the ring.

### Step 5: Draw the Alpha-Anomer of Maltose
1. Start with the cyclic form of the first glucose unit.
2. Attach the second glucose unit via an alpha 1,4-glycosidic bond. This means that the hydroxyl group on the first carbon of the second glucose unit will also be below the plane of the ring.
3. Ensure the substituents on the ring are correctly oriented: for the alpha-anomer, the OH group on the anomeric carbon (C1) of the first glucose is down.

The structure can be represented as follows:

```
O
/ \
C1 C1'
/ \
C2 C2'
/ \ / \
H OH OH H
| | | |
H H H CH2OH
```

### Step 6: Verify the Structure
Check the orientation of the hydroxyl groups:
- For the alpha-anomer, the hydroxyl group on the anomeric carbon (C1) should be down.
- The hydroxyl group on the second glucose unit (C1') should also be down, confirming the alpha configuration.

### Step 7: Compare with Given Options
Now, compare your drawn structure with the provided options to identify which one matches the alpha-anomer of maltose.

### Conclusion
The correct structure of the alpha-anomer of maltose is the one where the hydroxyl groups on the anomeric carbons are positioned downwards.

---